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Tsaturyan Y, Barg A, Simonsen A, Villanueva LG, Schmid S, Schliesser A and Polzik ES (2014), "Demonstration of suppressed phonon tunneling losses in phononic bandgap shielded membrane resonators for high-Q optomechanics", Optics Express. Vol. 22(6), pp. 6810. Optical Society of America (OSA).
Abstract: Dielectric membranes with exceptional mechanical and optical properties present one of the most promising platforms in quantum opto-mechanics. The performance of stressed silicon nitride nanomembranes as mechanical resonators notoriously depends on how their frame is clamped to the sample mount, which in practice usually necessitates delicate, and difficult-to-reproduce mounting solutions. Here, we demonstrate that a phononic bandgap shield integrated in the membrane’s silicon frame eliminates this dependence, by suppressing dissipation through phonon tunneling. We dry-etch the membrane’s frame so that it assumes the form of a cm-sized bridge featuring a 1-dimensional periodic pattern, whose phononic density of states is tailored to exhibit one, or several, full band gaps around the membrane’s high-Q modes in the MHz-range. We quantify the effectiveness of this phononic bandgap shield by optical interferometry measuring both the suppressed transmission of vibrations, as well as the influence of frame clamping conditions on the membrane modes. We find suppressions up to 40 dB and, for three different realized phononic structures, consistently observe significant suppression of the dependence of the membrane’s modes on sample clamping—if the mode’s frequency lies in the bandgap. As a result, we achieve membrane mode quality factors of 5 × 10^6 with samples that are tightly bolted to the 8 K-cold finger of a cryostat. Q × f -products of 6 × 10^12 Hz at 300 K and 14 × 10^12 Hz at 8 K are observed, satisfying one of the main requirements for optical cooling of mechanical vibrations to their quantum ground-state.
BibTeX:
@article{Tsaturyan2014,
  author = {Tsaturyan, Yeghishe and Barg, Andreas and Simonsen, Anders and Villanueva, Luis Guillermo and Schmid, Silvan and Schliesser, Albert and Polzik, Eugene S.},
  title = {Demonstration of suppressed phonon tunneling losses in phononic bandgap shielded membrane resonators for high-Q optomechanics},
  journal = {Optics Express},
  publisher = {Optical Society of America (OSA)},
  year = {2014},
  volume = {22},
  number = {6},
  pages = {6810},
  doi = {10.1364/oe.22.006810},
  eprint = {1312.7776}
}
Bağcı T, Simonsen A, Schmid S, Villanueva LG, Zeuthen E, Appel J, Taylor JM, Sørensen A, Usami K, Schliesser A and Polzik ES (2014), "Optical detection of radio waves through a nanomechanical transducer", Nature., March, 2014. Vol. 507, pp. 81-85.
Abstract: Low-loss transmission and sensitive recovery of weak radio-frequency and microwave signals is a ubiquitous challenge, crucial in radio astronomy, medical imaging, navigation, and classical and quantum communication. Efficient up-conversion of radio-frequency signals to an optical carrier would enable their transmission through optical fibres instead of through copper wires, drastically reducing losses, and would give access to the set of established quantum optical techniques that are routinely used in quantum-limited signal detection. Research in cavity optomechanics has shown that nanomechanical oscillators can couple strongly to either microwave or optical fields. Here we demonstrate a room-temperature optoelectromechanical transducer with both these functionalities, following a recent proposal using a high-quality nanomembrane. A voltage bias of less than 10 V is sufficient to induce strong coupling between the voltage fluctuations in a radio-frequency resonance circuit and the membrane's displacement, which is simultaneously coupled to light reflected off its surface. The radio-frequency signals are detected as an optical phase shift with quantum-limited sensitivity. The corresponding half-wave voltage is in the microvolt range, orders of magnitude less than that of standard optical modulators. The noise of the transducer--beyond the measured Johnson noise of the resonant circuit--consists of the quantum noise of light and thermal fluctuations of the membrane, dominating the noise floor in potential applications in radio astronomy and nuclear magnetic imaging. Each of these contributions is inferred to be when balanced by choosing an electromechanical cooperativity of with an optical power of 1 mW. The noise temperature of the membrane is divided by the cooperativity. For the highest observed cooperativity of , this leads to a projected noise temperature of 40 mK and a sensitivity limit of . Our approach to all-optical, ultralow-noise detection of classical electronic signals sets the stage for coherent up-conversion of low-frequency quantum signals to the optical domain.
BibTeX:
@article{Bagci2014, author = {Bağcı, T. and Simonsen, A. and Schmid, S. and Villanueva, L.~G. and Zeuthen,
                    E. and Appel, J. and Taylor, J.~M. and Sørensen, A. and Usami, K. and Schliesser, A. and Polzik,
                    E.~S.}, title = {Optical detection of radio waves through a nanomechanical transducer}, journal = {Nature},
                    year = {2014}, month = {March}, volume = {507}, pages = {81--85}, doi = {10.1038/nature13029}, eprint
                    = {1307.3467} }
Christensen SL, Béguin J-B, Bookjans E, Sørensen HL, Müller JH, Appel J and Polzik ES (2014), "Quantum interference of a single spin excitation with a macroscopic atomic ensemble", Phys. Rev. A., March, 2014. Vol. 89(3), pp. 033801.
Abstract: We report on the observation of quantum interference of a collective single spin excitation with a spin ensemble of Na≈105 atoms. Detection of a single photon scattered from the atoms creates the single spin excitation, a Fock state embedded in the collective spin of the ensemble. The state of the atomic ensemble is then detected by a quantum nondemolition measurement of the collective spin. A macroscopic difference of the order of √N a in the marginal distribution of the collective spin state arises from the interference between the single excited spin and Na atoms. These hybrid discrete-continuous manipulation and measurement procedures of collective spin states in an atomic ensemble pave the road towards generation of even more exotic ensemble states for quantum information processing, precision measurements, and communication.
BibTeX:
@article{Christensen2014, author = {Christensen, S.~L. and Béguin, J.-B. and Bookjans, E. and
                    Sørensen, H.~L. and Müller, J.~H. and Appel, J. and Polzik, E.~S.}, title = {Quantum interference
                    of a single spin excitation with a macroscopic atomic ensemble}, journal = {Phys. Rev. A}, year = {2014},
                    month = {March}, volume = {89}, number = {3}, pages = {033801}, doi = {10.1103/PhysRevA.89.033801}, eprint
                    = {1309.2514} }
Sørensen HL, Polzik ES and Appel J (2014), "Heater self-calibration technique for shape prediction of fiber tapers", J. Lightwave. Technol.., May, 2014. Vol. 32(10), pp. 1886-1891.
Abstract: In the production of tapered optical fibers complete control over the resulting spatial shape is desired. This is important to optimize the fiber shape according to application- dependent requirements as well as to ensure adiabatic tapers. Especially in the transition regions the fiber shape depends on the heater properties and in general a fluid dynamical model including the axial viscosity profile is required. The latter can be hard to access and is therefore often approximated by assuming a box-shaped temperature distribution. We present a method for easy experimental calibration of the axial viscosity profile within the heater. This allows the determination of the resultant fiber shape for arbitrary pulling procedures, using only an additional camera and the fiber drawing setup itself. We find very good agreement between the modeled and measured fiber shape.
BibTeX:
@article{Soerensen2014, author = {Heidi L. Sørensen and Eugene S. Polzik and Jürgen Appel},
                    title = {Heater self-calibration technique for shape prediction of fiber tapers}, journal = {J. Lightwave.
                    Technol.}, year = {2014}, month = {May}, volume = {32}, number = {10}, pages = {1886--1891}, doi = {10.1109/JLT.2014.2314319},
                    eprint = {1312.3840} }
Tsaturyan Y, Barg A, Simonsen A, Villanueva LG, Schmid S, Schliesser A and Polzik ES (2014), "Demonstration of suppressed phonon tunneling losses in phononic bandgap shielded membrane resonators for high-Q optomechanics", Optics Express. Vol. 22(6), pp. 6810. Optical Society of America (OSA).
BibTeX:
@article{Tsaturyan_2014, author = {Tsaturyan, Yeghishe and Barg, Andreas and Simonsen, Anders and Villanueva,
                    Luis Guillermo and Schmid, Silvan and Schliesser, Albert and Polzik, Eugene S.}, title = {Demonstration
                    of suppressed phonon tunneling losses in phononic bandgap shielded membrane resonators for high-Q optomechanics},
                    journal = {Optics Express}, publisher = {Optical Society of America (OSA)}, year = {2014}, volume = {22},
                    number = {6}, pages = {6810}, url = {http://dx.doi.org/10.1364/OE.22.006810}, doi = {10.1364/oe.22.006810},
                    eprint = {1312.7776} }
Christensen SL, Béguin JB, Sørensen HL, Bookjans E, Oblak D, Müller JH, Appel J and Polzik ES (2013), "Towards quantum state tomography of a single polariton state of an atomic ensemble", New Journal of Physics, Focus issue on Quantum Tomography., January, 2013. Vol. 15(1), pp. 015002.
Abstract: We present a proposal and a feasibility study for the creation and quantum state tomography of a single polariton state of an atomic ensemble. The collective non-classical and non-Gaussian state of the ensemble is generated by detection of a single forward scattered photon. The state is subsequently characterized by atomic state tomography performed using strong dispersive light-atoms interaction followed by a homodyne measurement on the transmitted light. The proposal is backed by preliminary experimental results showing projection noise limited sensitivity and a simulation demonstrating the feasibility of the proposed method for detection of a non-classical and non-Gaussian state of the mesoscopic atomic ensemble. This work represents the first attempt of hybrid discrete-continuous variable quantum state processing with atomic ensembles.
BibTeX:
@article{Christensen2013, author = {Christensen, S. L. and Béguin, J. B. and Sørensen,
                    H. L. and Bookjans, E. and Oblak, D. and Müller, J. H. and Appel, J. and Polzik, E.~S.}, title =
                    {Towards quantum state tomography of a single polariton state of an atomic ensemble}, journal = {New
                    Journal of Physics, Focus issue on Quantum Tomography}, year = {2013}, month = {January}, volume = {15},
                    number = {1}, pages = {015002}, doi = {10.1088/1367-2630/15/1/015002}, eprint = {1208.1415} }
Krauter H, Salart D, Muschik C, Petersen JM, Shen H, Fernholz T and Polzik E (2013), "Deterministic quantum teleportation between distant atomic objects", Nature Physics., June, 2013.
Abstract: Quantum teleportation is a key ingredient in quantum networks, and one of the building blocks for quantum computation. Teleportation between distant material objects using light as the quantum-information carrier has been a particularly exciting goal. Here we propose and demonstrate the deterministic continuous-variable teleportation between distant material objects. The objects are macroscopic atomic ensembles at room temperature. Entanglement required for teleportation is distributed by light propagating from one ensemble to the other. We demonstrate that the experimental fidelity of the quantum teleportation is higher than that achievable by any classical process. Furthermore, we demonstrate the benefits of deterministic teleportation by teleporting a sequence of spin states evolving in time from one distant object onto another. The teleportation protocol is applicable to other important systems, such as mechanical oscillators coupled to light or cold spin ensembles coupled to microwaves.
BibTeX:
@article{Krauter2013, author = {Krauter, H. and Salart, D. and Muschik, C.A. and Petersen, J. M. and
                    Shen, Heng and Fernholz, T. and Polzik, E.S.}, title = {Deterministic quantum teleportation between distant
                    atomic objects}, journal = {Nature Physics}, year = {2013}, month = {June}, doi = {10.1038/nphys2631},
                    eprint = {1212.6746} }
Kaminski F, Kampel NS, Steenstrup MPH, Griesmaier A, Polzik ES and Müller JH (2012), "In-Situ Dual-Port Polarization Contrast Imaging of Faraday Rotation in a High Optical Depth Ultracold 87Rb Atomic Ensemble", European Journal of Physics D., September, 2012. Vol. 66, pp. 227.
Abstract: We study the effects of high optical depth and density on the performance of a light-atom quantum interface. An in-situ imaging method, a dual-port polarization contrast technique, is presented. This technique is able to compensate for image distortions due to refraction. We propose our imaging method as a tool to characterize atomic ensembles for high capacity spatial multimode quantum memories. Ultracold dense inhomogeneous Rubidium samples are imaged and we find a resonant optical depth as high as 680 on the D1 line. The measurements are compared with light-atom interaction models based on Maxwell-Bloch equations. We find that an independent atom assumption is insufficient to explain our data and present corrections due to resonant dipole-dipole interactions.
BibTeX:
@article{Kaminski2012, author = {Kaminski, F. and Kampel, N.~S. and Steenstrup, M.~P.~H. and Griesmaier,
                    A. and Polzik, E.~S. and Müller, J.~H.}, title = {In-Situ Dual-Port Polarization Contrast Imaging
                    of Faraday Rotation in a High Optical Depth Ultracold 87Rb Atomic Ensemble}, journal = {European Journal
                    of Physics D}, year = {2012}, month = {September}, volume = {66}, pages = {227}, doi = {10.1140/epjd/e2012-30038-0},
                    eprint = {1209.0380} }
Kiesel T, Vogel W, Christensen SL, Béguin J-B, Appel J and Polzik ES (2012), "Atomic nonclassicality quasiprobabilities", Phys. Rev. A., October, 2012. Vol. 86, pp. 042108.
Abstract: Although nonclassical quantum states are important both conceptually and as a resource for quantum technology, it is often difficult to test whether a given quantum system displays nonclassicality. A simple method to certify nonclassicality is introduced, based on easily accessible collective atomic quadrature measurements, without the need of full state tomography. The statistics is analyzed beyond the ground-state noise level, by direct sampling of a regularized atomic quadrature quasiprobability. Nonclassicality of a squeezed ensemble of 2x10^5 Cesium atoms is demonstrated, with a significance of up to 23 standard deviations.
BibTeX:
@article{Kiesel2012, author = {Kiesel, T. and Vogel, W. and Christensen, S.~L. and Béguin, J.-B.
                    and Appel, J. and Polzik, E.~S.}, title = {Atomic nonclassicality quasiprobabilities}, journal = {Phys.
                    Rev. A}, year = {2012}, month = {October}, volume = {86}, pages = {042108}, doi = {10.1103/PhysRevA.86.042108},
                    eprint = {1207.3314} }
Jensen K, Wasilewski W, Krauter H, Fernholz T, Nielsen BM, Owari M, Plenio MB, Serafini A, Wolf MM and Polzik ES (2011), "Quantum memory for entangled continuous-variable states", Nature Physics., January, 2011. Vol. 7, pp. 13-16.
Abstract: A quantum memory for light is a key element for the realization of future quantum information networks. Requirements for a good quantum memory are versatility (allowing a wide range of inputs) and preservation of quantum information in a way unattainable with any classical memory device. Here we demonstrate such a quantum memory for continuous-variable entangled states, which play a fundamental role in quantum information processing. We store an extensive alphabet of two-mode 6.0dB squeezed states obtained by varying the orientation of squeezing and the displacement of the states. The two components of the entangled state are stored in two room-temperature cells separated by 0.5m, one for each mode, with a memory time of 1ms. The true quantum character of the memory is rigorously proved by showing that the experimental memory fidelity 0.52+/-0.02 significantly exceeds the benchmark of 0.45 for the best possible classical memory for a range of displacements.
BibTeX:
@article{Jensen2011, author = {Jensen, K. and Wasilewski, W. and Krauter, H. and Fernholz, T. and Nielsen,
                    B.~M. and Owari, M. and Plenio, M.~B. and Serafini, A. and Wolf, M.~M. and Polzik, E.~S.}, title = {Quantum
                    memory for entangled continuous-variable states}, journal = {Nature Physics}, year = {2011}, month =
                    {January}, volume = {7}, pages = {13--16}, doi = {10.1038/nphys1819}, eprint = {1002.1920} }
Krauter H, Muschik CA, Jensen K, Wasilewski W, Petersen JM, Cirac JI and Polzik ES (2011), "Entanglement Generated by Dissipation and Steady State Entanglement of Two Macroscopic Objects", Phys. Rev. Lett.., August, 2011. Vol. 107(8), pp. 080503-+.
Abstract: Entanglement is a striking feature of quantum mechanics and an essential ingredient in most applications in quantum information. Typically, coupling of a system to an environment inhibits entanglement, particularly in macroscopic systems. Here we report on an experiment where dissipation continuously generates entanglement between two macroscopic objects. This is achieved by engineering the dissipation using laser and magnetic fields, and leads to robust event-ready entanglement maintained for 0.04 s at room temperature. Our system consists of two ensembles containing about 1012 atoms and separated by 0.5 m coupled to the environment composed of the vacuum modes of the electromagnetic field. By combining the dissipative mechanism with a continuous measurement, steady state entanglement is continuously generated and observed for up to 1 h.
BibTeX:
@article{Krauter2011, author = {Krauter, H. and Muschik, C.~A. and Jensen, K. and Wasilewski, W. and
                    Petersen, J.~M. and Cirac, J.~I. and Polzik, E.~S.}, title = {Entanglement Generated by Dissipation and
                    Steady State Entanglement of Two Macroscopic Objects}, journal = {Phys. Rev. Lett.}, year = {2011}, month
                    = {August}, volume = {107}, number = {8}, pages = {080503-+}, doi = {10.1103/PhysRevLett.107.080503},
                    eprint = {1006.4344} }
Muschik C, Krauter H, Jensen K, Wasilewski W, Petersen JM, Cirac I and Polzik E (2011), "Entanglement Generated by Dissipation", International Conference on Quantum Information., In International Conference on Quantum Information. , pp. QMH1. Optical Society of America.
Abstract: We present a robust method for generating entanglement by engineered dissipation. Two atomic ensembles are kept entangled for 0.04s. By combining the purely dissipative mechanism with measurements, steady state entanglement is observed for up to an hour.
BibTeX:
@inproceedings{Muschik2011b, author = {Christine Muschik and Hanna Krauter and Kasper Jensen and Wojciech
                    Wasilewski and Jonas Meyer Petersen and Ignacio Cirac and Eugene Polzik}, title = {Entanglement Generated
                    by Dissipation}, booktitle = {International Conference on Quantum Information}, journal = {International
                    Conference on Quantum Information}, publisher = {Optical Society of America}, year = {2011}, pages =
                    {QMH1}, url = {http://www.opticsinfobase.org/abstract.cfm?URI=ICQI-2011-QMH1} }
Simon C and Polzik ES (2011), "Fock-state view of weak-value measurements and implementation with photons and atomic ensembles", Phys. Rev. A., April, 2011. Vol. 83(4), pp. 040101.
Abstract: Weak measurements in combination with postselection can give rise to a striking amplification effect (related to a large “weak value”). We show that this effect can be understood by viewing the initial state of the pointer as the ground state of a fictional harmonic oscillator. This perspective clarifies the relationship between the weak-value regime and other measurement techniques and inspires a proposal to implement fully quantum weak-value measurements combining photons and atomic ensembles.
BibTeX:
@article{Simon2011, author = {Simon, C. and Polzik, E.~S.}, title = {Fock-state view of weak-value measurements
                    and implementation with photons and atomic ensembles}, journal = {Phys. Rev. A}, year = {2011}, month
                    = {April}, volume = {83}, number = {4}, pages = {040101}, doi = {10.1103/PhysRevA.83.040101}, eprint
                    = {1010.3695} }
Balabas MV, Jensen K, Wasilewski W, Krauter H, Madsen LS, Müller JH, Fernholz T and Polzik ES (2010), "High quality anti-relaxation coating material for alkali atom vapor cells", Opt. Express., March, 2010. Vol. 18(6), pp. 5825-5830. OSA.
Abstract: We present an experimental investigation of alkali atom vapor cells coated with a high quality anti-relaxation coating material based on alkenes. The prepared cells with single compound alkene based coating showed the longest spin relaxation times which have been measured up to now with room temperature vapor cells. Suggestions are made that chemical binding of a cesium atom and an alkene molecule by attack to the C $=$ C bond plays a crucial role in such improvement of anti-relaxation coating quality.
BibTeX:
@article{Balabas:10, author = {M. V. Balabas and K. Jensen and W. Wasilewski and H. Krauter and L. S.
                    Madsen and J. H. Müller and T. Fernholz and E. S. Polzik}, title = {High quality anti-relaxation
                    coating material for alkali atom vapor cells}, journal = {Opt. Express}, publisher = {OSA}, year = {2010},
                    month = {March}, volume = {18}, number = {6}, pages = {5825--5830}, doi = {10.1364/OE.18.005825}, eprint
                    = {0911.5274} }
Hammerer K, Sørensen A and Polzik E (2010), "Quantum interface between light and atomic ensembles", Rev. Mod. Phys.., April, 2010. Vol. 82, pp. 1041-1093.
Abstract: During the past decade the interaction of light with multi-atom ensembles has attracted a lot of attention as a basic building block for quantum information processing and quantum state engineering. The field started with the realization that optically thick free space ensembles can be efficiently interfaced with quantum optical fields. By now the atomic ensemble - light interfaces have become a powerful alternative to the cavity-enhanced interaction of light with single atoms. We discuss various mechanisms used for the quantum interface, including quantum nondemolition or Faraday interaction, quantum measurement and feedback, Raman interaction and electromagnetically induced transparency. The paper provides a common theoretical frame for these processes, describes basic experimental techniques and media used for quantum interfaces, and reviews several key experiments on quantum memory for light, quantum entanglement between atomic ensembles and light, and quantum teleportation with atomic ensembles. We discuss the two types of quantum measurements which are most important for the interface: homodyne detection and photon counting. The paper concludes with an outlook on the future of atomic ensembles as an enabling technology in quantum information processing.
BibTeX:
@article{Hammerer2010, author = {K. Hammerer and A.S. Sørensen and E.S. Polzik}, title = {Quantum
                    interface between light and atomic ensembles}, journal = {Rev. Mod. Phys.}, year = {2010}, month = {April},
                    volume = {82}, pages = {1041--1093}, doi = {10.1103/RevModPhys.82.1041}, eprint = {0807.3358} }
Appel J, Renema J, Oblak D, Louchet-Chauvet A, Kjærgaard N and Polzik E (2010), "Mesoscopic Non-classical Atomic States for Quantum Information and Metrology", In Latin America Optics and Photonics Conference. (September) Optical Society of America.
BibTeX:
@inproceedings{J.Appel2010, author = {J. Appel and J. Renema and D. Oblak and A. Louchet-Chauvet and
                    N. Kjærgaard and E. Polzik}, title = {Mesoscopic Non-classical Atomic States for Quantum Information
                    and Metrology}, booktitle = {Latin America Optics and Photonics Conference}, publisher = {Optical Society
                    of America}, year = {2010}, number = {September}, series = {OSA Technical Digest}, url = {http://www.opticsinfobase.org/abstract.cfm?URI=LAOP-2010-WG1}
                    }
Usami K, Naesby A, Bagci T, Nielsen BM, Liu J, Stobbe S, Lodahl P and Polzik ES (2010), "Optoelectronic cooling of mechanical modes in a semiconductor nanomembrane"
BibTeX:
@article{K.Usami2010, author = {K. Usami and A. Naesby and T. Bagci and B.~Melholt Nielsen and J. Liu
                    and S. Stobbe and P. Lodahl and E.~S. Polzik}, title = {Optoelectronic cooling of mechanical modes in
                    a semiconductor nanomembrane}, year = {2010}, eprint = {1011.3974} }
Krauter H, Sherson J and Polzik E (2010), "Quantum state transfer between light and matter via teleportation", Laser & Photonics Reviews. Vol. 4(6), pp. 685-696. WILEY-VCH Verlag.
Abstract: Abstract Quantum teleportation is an interesting feature of quantum mechanics. Entanglement is used as a link between two remote locations to transfer a quantum state without physically sending it – a process that cannot be realized utilizing merely classical tools. Furthermore it has become evident that teleportation is also an important element of future quantum networks and it can be an ingredient for quantum computation. This article reports for the first time the teleportation from light to atoms. In the experiment discussed, the quantum state of a light beam is transferred to an atomic ensemble. The key element of light-atom entanglement created via a dispersive interaction lays the foundation for the protocol.
BibTeX:
@article{Krauter2010a, author = {Krauter, H. and Sherson, J.F. and Polzik, E.S.}, title = {Quantum state
                    transfer between light and matter via teleportation}, journal = {Laser & Photonics Reviews}, publisher
                    = {WILEY-VCH Verlag}, year = {2010}, volume = {4}, number = {6}, pages = {685--696}, doi = {10.1002/lpor.200900021}
                    }
Louchet-Chauvet A, Appel J, Renema JJ, Oblak D, Kjærgaard N and Polzik ES (2010), "Entanglement-assisted atomic clock beyond the projection noise limit", New. J. Phys.., June, 2010. Vol. 12(6), pp. 065032-+.
Abstract: We use a quantum non-demolition measurement to generate a spin squeezed state and to create entanglement in a cloud of 105 cold cesium atoms. For the first time we operate an atomic clock improved by spin squeezing beyond the projection noise limit in a proof-of-principle experiment. For a clock-interrogation time of 10 μs, the experiments show an improvement of 1.1 dB in the signal-to-noise ratio, compared to the atomic projection noise limit.
BibTeX:
@article{Louchet-Chauvet2010, author = {Louchet-Chauvet, A. and Appel, J. and Renema, J.~J. and Oblak,
                    D. and Kjærgaard, N. and Polzik, E.~S.}, title = {Entanglement-assisted atomic clock beyond the
                    projection noise limit}, journal = {New. J. Phys.}, year = {2010}, month = {June}, volume = {12}, number
                    = {6}, pages = {065032-+}, doi = {10.1088/1367-2630/12/6/065032}, eprint = {0912.3895} }
Simon C, Afzelius M, Appel J, Boyer de La Giroday A, Dewhurst SJ, Gisin N, Hu CY, Jelezko F, Kröll S, Müller JH, Nunn J, Polzik ES, Rarity JG, de Riedmatten H, Rosenfeld W, Shields AJ, Sköld N, Stevenson RM, Thew R, Walmsley IA, Weber MC, Weinfurter H, Wrachtrup J and Young RJ (2010), "Quantum memories. A review based on the European integrated project `Qubit Applications (QAP)'", European Physical Journal D., May, 2010. Vol. 58, pp. 1-22.
Abstract: We perform a review of various approaches to the implementation of quantum memories, with an emphasis on activities within the quantum memory sub-project of the EU integrated project “Qubit Applications”. We begin with a brief overview over different applications for quantum memories and different types of quantum memories. We discuss the most important criteria for assessing quantum memory performance and the most important physical requirements. Then we review the different approaches represented in “Qubit Applications” in some detail. They include solid-state atomic ensembles, NV centers, quantum dots, single atoms, atomic gases and optical phonons in diamond. We compare the different approaches using the discussed criteria.
BibTeX:
@article{Simon2010, author = {Simon, C. and Afzelius, M. and Appel, J. and Boyer de La Giroday, A. and
                    Dewhurst, S.~J. and Gisin, N. and Hu, C.~Y. and Jelezko, F. and Kröll, S. and Müller, J.~H.
                    and Nunn, J. and Polzik, E.~S. and Rarity, J.~G. and de Riedmatten, H. and Rosenfeld, W. and Shields,
                    A.~J. and Sköld, N. and Stevenson, R.~M. and Thew, R. and Walmsley, I.~A. and Weber, M.~C. and Weinfurter,
                    H. and Wrachtrup, J. and Young, R.~J.}, title = {Quantum memories. A review based on the European integrated
                    project `Qubit Applications (QAP)'}, journal = {European Physical Journal D}, year = {2010}, month =
                    {May}, volume = {58}, pages = {1--22}, doi = {10.1140/epjd/e2010-00103-y}, eprint = {1003.1107} }
Vasilyev DV, Sokolov IV and Polzik ES (2010), "Quantum volume hologram", Physical Review A., February, 2010. Vol. 81(2), pp. 020302-+.
Abstract: We propose a scheme for parallel spatially multimode quantum memory for light. The scheme is based on a counterpropagating quantum signal wave and a strong classical reference wave as in a classical volume hologram and therefore can be called a quantum volume hologram. The medium for the hologram consists of a spatially extended ensemble of atoms placed in a magnetic field. The write-in and readout of this quantum hologram is as simple as that of its classical counterpart and consists of a single-pass illumination. In addition, we show that the present scheme for a quantum hologram is less sensitive to diffraction and therefore is capable of achieving a higher density of storage of spatial modes as compared to previous proposals. We present a feasibility study and show that experimental implementation is possible with available cold atomic samples. A quantum hologram capable of storing entangled images can become an important ingredient in quantum information processing and quantum imaging.
BibTeX:
@article{Vasilyev2010, author = {Vasilyev, D.~V. and Sokolov, I.~V. and Polzik, E.~S.}, title = {Quantum
                    volume hologram}, journal = {Physical Review A}, year = {2010}, month = {February}, volume = {81}, number
                    = {2}, pages = {020302-+}, doi = {10.1103/PhysRevA.81.020302}, eprint = {0906.1528} }
Wasilewski W, Jensen K, Krauter H, Renema JJ, Balabas MV and Polzik ES (2010), "Quantum Noise Limited and Entanglement-Assisted Magnetometry", Phys. Rev. Lett.., April, 2010. Vol. 104(13), pp. 133601-+.
Abstract: We study experimentally the fundamental limits of sensitivity of an atomic radio-frequency magnetometer. First, we apply an optimal sequence of state preparation, evolution, and the backaction evading measurement to achieve a nearly projection noise limited sensitivity. We furthermore experimentally demonstrate that Einstein-Podolsky-Rosen entanglement of atoms generated by a measurement enhances the sensitivity to pulsed magnetic fields. We demonstrate this quantum limited sensing in a magnetometer utilizing a truly macroscopic ensemble of 1.5×1012atoms which allows us to achieve subfemtotesla/Hz sensitivity.
BibTeX:
@article{Wasilewski2010, author = {Wasilewski, W. and Jensen, K. and Krauter, H. and Renema, J.~J. and
                    Balabas, M.~V. and Polzik, E.~S.}, title = {Quantum Noise Limited and Entanglement-Assisted Magnetometry},
                    journal = {Phys. Rev. Lett.}, year = {2010}, month = {April}, volume = {104}, number = {13}, pages =
                    {133601-+}, doi = {10.1103/PhysRevLett.104.133601}, eprint = {0907.2453} }
Appel J, Windpassinger PJ, Oblak D, Busk Hoff U, Kjærgaard N and Polzik ES (2009), "Mesoscopic atomic entanglement for precision measurements beyond the standard quantum limit", P. Natl. Acad. Sci.., June, 2009. Vol. 106, pp. 10960-10965.
Abstract: Squeezing of quantum fluctuations by means of entanglement is a well recognized goal in the field of quantum information science and precision measurements. In particular, squeezing the fluctuations via entanglement between two-level atoms can improve the precision of sensing, clocks, metrology, and spectroscopy. Here, we demonstrate 3.4 dB of metrologically relevant squeezing and entanglement for ~ 10^5 cold cesium atoms via a quantum nondemolition (QND) measurement on the atom clock levels. We show that there is an optimal degree of decoherence induced by the quantum measurement which maximizes the generated entanglement. A two-color QND scheme used in this paper is shown to have a number of advantages for entanglement generation as compared to a single color QND measurement.
BibTeX:
@article{Appel2009, author = {Appel, J. and Windpassinger, P.~J. and Oblak, D. and Busk Hoff, U. and
                    Kjærgaard, N. and Polzik, E.~S.}, title = {Mesoscopic atomic entanglement for precision measurements
                    beyond the standard quantum limit}, journal = {P. Natl. Acad. Sci.}, year = {2009}, month = {June}, volume
                    = {106}, pages = {10960--10965}, doi = {10.1073/pnas.0901550106}, eprint = {0810.3545} }
Appel J, MacRae A and Lvovsky AI (2009), "A versatile digital GHz phase lock for external cavity diode lasers", Measurement Science and Technology., May, 2009. Vol. 20(5), pp. 055302-+.
Abstract: We present a versatile, inexpensive and simple optical phase lock for applications in atomic physics experiments. Thanks to all-digital phase detection and implementation of beat frequency pre-scaling, the apparatus requires no microwave-range reference input and permits phase locking at frequency differences ranging from sub-MHz to 7 GHz (and with minor extension to 12 GHz). The locking range thus covers ground-state hyperfine splittings of all alkali metals, which makes this system a universal tool for many experiments on coherent interaction between light and atoms.
BibTeX:
@article{Appel2009a, author = {Appel, J. and MacRae, A. and Lvovsky, A.~I.}, title = {A versatile digital
                    GHz phase lock for external cavity diode lasers}, journal = {Measurement Science and Technology}, year
                    = {2009}, month = {May}, volume = {20}, number = {5}, pages = {055302-+}, doi = {10.1088/0957-0233/20/5/055302},
                    eprint = {0809.3607} }
Hammerer K, Aspelmeyer M, Polzik ES and Zoller P (2009), "Establishing Einstein-Poldosky-Rosen Channels between Nanomechanics and Atomic Ensembles", Physical Review Letters., January, 2009. Vol. 102(2), pp. 020501-+.
Abstract: We suggest interfacing nanomechanical systems via an optical quantum bus to atomic ensembles, for which means of high precision state preparation, manipulation, and measurement are available. This allows, in particular, for a quantum nondemolition Bell measurement, projecting the coupled system, atomic-ensemble-nanomechanical resonator, into an entangled EPR state. The entanglement is observable even for nanoresonators initially well above their ground states and can be utilized for teleportation of states from an atomic ensemble to the mechanical system.
BibTeX:
@article{Hammerer2009a, author = {Hammerer, K. and Aspelmeyer, M. and Polzik, E.~S. and Zoller, P.},
                    title = {Establishing Einstein-Poldosky-Rosen Channels between Nanomechanics and Atomic Ensembles}, journal
                    = {Physical Review Letters}, year = {2009}, month = {January}, volume = {102}, number = {2}, pages =
                    {020501-+}, doi = {10.1103/PhysRevLett.102.020501}, eprint = {0804.3005} }
Jähne K, Genes C, Hammerer K, Wallquist M, Polzik ES and Zoller P (2009), "Cavity-assisted squeezing of a mechanical oscillator", Physical Review A., June, 2009. Vol. 79(6), pp. 063819-+.
Abstract: We investigate the creation of squeezed states of a vibrating membrane or a movable mirror in an optomechanical system. An optical cavity is driven by the squeezed light and couples via the radiation pressure to the membrane or mirror, effectively providing a squeezed heat bath for the mechanical oscillator. Under the conditions of laser cooling to the ground state, we find an efficient transfer of squeezing with roughly $60 of light squeezing conveyed to the membrane or mirror (on a dB scale). We determine the requirements on the carrier frequency and the bandwidth of squeezed light. Beyond the conditions of ground-state cooling, we predict mechanical squashing to be observable in current systems.
BibTeX:
@article{Jahne2009, author = {Jähne, K. and Genes, C. and Hammerer, K. and Wallquist, M. and Polzik,
                    E.~S. and Zoller, P.}, title = {Cavity-assisted squeezing of a mechanical oscillator}, journal = {Physical
                    Review A}, year = {2009}, month = {June}, volume = {79}, number = {6}, pages = {063819-+}, doi = {10.1103/PhysRevA.79.063819},
                    eprint = {0904.1306} }
Jensen K, Acosta VM, Higbie JM, Ledbetter MP, Rochester SM and Budker D (2009), "Cancellation of nonlinear Zeeman shifts with light shifts", Physical Review A., February, 2009. Vol. 79(2), pp. 023406-+.
Abstract: Nonlinear Zeeman (NLZ) shifts arising from magnetic-field mixing of the two hyperfine ground states in alkali-metal atoms lead to splitting of magnetic-resonance lines. This is a major source of sensitivity degradation and the so-called “heading errors” of alkali-metal-vapor atomic magnetometers operating in the geophysical field range (B≈0.2-0.7G) . Here, it is shown theoretically and experimentally that NLZ shifts can be effectively canceled by light shifts caused by a laser field of appropriate intensity, polarization, and frequency, a technique that can be readily applied in practical situations.
BibTeX:
@article{Jensen2009, author = {Jensen, K. and Acosta, V.~M. and Higbie, J.~M. and Ledbetter, M.~P. and
                    Rochester, S.~M. and Budker, D.}, title = {Cancellation of nonlinear Zeeman shifts with light shifts},
                    journal = {Physical Review A}, year = {2009}, month = {February}, volume = {79}, number = {2}, pages
                    = {023406-+}, doi = {10.1103/PhysRevA.79.023406}, eprint = {0810.2221} }
Kubasik M, Koschorreck M, Napolitano M, de Echaniz SR, Crepaz H, Eschner J, Polzik ES and Mitchell MW (2009), "Polarization-based light-atom quantum interface with an all-optical trap", Physical Review A., April, 2009. Vol. 79(4), pp. 043815-+.
Abstract: We describe the implementation of a system for studying light-matter interactions using an ensemble of 106 cold rubidium 87 atoms trapped in a single-beam optical dipole trap. In this configuration the elongated shape of the atomic cloud increases the strength of the collective light-atom coupling. Trapping all optically allows for long storage times in a low decoherence environment. We are able to perform several thousands of measurements on one atomic ensemble with little destruction. We report results on paramagnetic Faraday rotations from a macroscopically polarized atomic ensemble. Our results confirm that strong light-atom coupling is achievable in this system which makes it attractive for single-pass quantum information protocols.
BibTeX:
@article{Kubasik2009, author = {Kubasik, M. and Koschorreck, M. and Napolitano, M. and de Echaniz, S.~R.
                    and Crepaz, H. and Eschner, J. and Polzik, E.~S. and Mitchell, M.~W.}, title = {Polarization-based light-atom
                    quantum interface with an all-optical trap}, journal = {Physical Review A}, year = {2009}, month = {April},
                    volume = {79}, number = {4}, pages = {043815-+}, doi = {10.1103/PhysRevA.79.043815}, eprint = {0812.4863}
                    }
Nielsen PM, Schori C, Sørensen JL, Salvail L, Damgard I and Polzik E (2009), "Experimental quantum key distribution with proven security against realistic attacks", Journal of Modern Optics., September, 2009. Vol. 48(13), pp. 1921-1942.
BibTeX:
@article{Nielsen2009a, author = {Peter~Moller Nielsen and Christian Schori and Jens~Lykke Sørensen
                    and Louis Salvail and Ivan Damgard and Eugene Polzik}, title = {Experimental quantum key distribution
                    with proven security against realistic attacks}, journal = {Journal of Modern Optics}, year = {2009},
                    month = {September}, volume = {48}, number = {13}, pages = {1921--1942}, doi = {10.1080/09500340108240897}
                    }
Roscilde T, Rodríguez M, Eckert K, Romero-Isart O, Lewenstein M, Polzik E and Sanpera A (2009), "Quantum polarization spectroscopy of correlations in attractive fermionic gases", New Journal of Physics., May, 2009. Vol. 11(5), pp. 055041-+.
Abstract: We show how spin-spin correlations, detected in a non-destructive way via spatially resolved quantum polarization spectroscopy, strongly characterize various phases realized in trapped ultracold fermionic atoms. Polarization degrees of freedom of the light couple to spatially resolved components of the atomic spin. In this way, quantum fluctuations of matter are faithfully mapped onto those of light. In particular, we demonstrate that quantum spin polarization spectroscopy provides a direct method to detect the Fulde-Ferrell-Larkin-Ovchinnikov phase realized in a one-dimensional imbalanced Fermi system.
BibTeX:
@article{Roscilde2009, author = {Roscilde, T. and Rodríguez, M. and Eckert, K. and Romero-Isart,
                    O. and Lewenstein, M. and Polzik, E. and Sanpera, A.}, title = {Quantum polarization spectroscopy of
                    correlations in attractive fermionic gases}, journal = {New Journal of Physics}, year = {2009}, month
                    = {May}, volume = {11}, number = {5}, pages = {055041-+}, doi = {10.1088/1367-2630/11/5/055041}, eprint
                    = {0901.3091} }
Saffman M, Oblak D, Appel J and Polzik ES (2009), "Spin squeezing of atomic ensembles by multicolor quantum nondemolition measurements", Phys. Rev. A., February, 2009. Vol. 79(2), pp. 023831-+.
Abstract: We analyze the creation of spin squeezed atomic ensembles by simultaneous dispersive interactions with several optical frequencies. A judicious choice of optical parameters enables optimization of an interferometric detection scheme that suppresses inhomogeneous light shifts and keeps the interferometer operating in a balanced mode that minimizes technical noise. We show that when the atoms interact with two-frequency light tuned to cycling transitions the degree of spin squeezing ξ2 scales as ξ2˜1/d , where d is the resonant optical depth of the ensemble. In real alkali metal atoms there are loss channels and the scaling may be closer to ξ2˜1/d . Nevertheless the use of two frequencies provides a significant improvement in the degree of squeezing attainable as we show by quantitative analysis of nonresonant probing on the Cs D1 line. Two alternative configurations are analyzed: a Mach-Zehnder interferometer that uses spatial interference and an interaction with multifrequency amplitude modulated light that does not require a spatial interferometer.
BibTeX:
@article{Saffman2009, author = {Saffman, M. and Oblak, D. and Appel, J. and Polzik, E.~S.}, title =
                    {Spin squeezing of atomic ensembles by multicolor quantum nondemolition measurements}, journal = {Phys.
                    Rev. A}, year = {2009}, month = {February}, volume = {79}, number = {2}, pages = {023831-+}, doi = {10.1103/PhysRevA.79.023831},
                    eprint = {0808.0516} }
Wasilewski W, Fernholz T, Jensen K, Madsen LS, Krauter H, Muschik C and Polzik ES (2009), "Generation of two-mode squeezed and entangled light in a single temporal and spatial mode", Optics Express., July, 2009. Vol. 17, pp. 14444-+.
Abstract: We analyse a novel squeezing and entangling mechanism which is due to correlated Stokes and anti-Stokes photon forward scattering in a multi-level atom vapour. Following the proposal we present an experimental demonstration of 3.5 dB pulsed frequency nondegenerate squeezed (quadrature entangled) state of light using room temperature caesium vapour. The source is very robust and requires only a few milliwatts of laser power. The squeezed state is generated in the same spatial mode as the local oscillator and in a single temporal mode. The two entangled modes are separated by twice the Zeeman frequency of the vapour which can be widely tuned. The narrow-band squeezed light generated near an atomic resonance can be directly used for atom-based quantum information protocols. Its single temporal mode characteristics make it a promising resource for quantum information processing.
BibTeX:
@article{Wasilewski2009a, author = {Wasilewski, W. and Fernholz, T. and Jensen, K. and Madsen, L.~S.
                    and Krauter, H. and Muschik, C. and Polzik, E.~S.}, title = {Generation of two-mode squeezed and entangled
                    light in a single temporal and spatial mode}, journal = {Optics Express}, year = {2009}, month = {July},
                    volume = {17}, pages = {14444-+}, doi = {10.1364/OE.17.014444}, eprint = {0907.0132} }
Windpassinger PJ, Oblak D, Busk Hoff U, Louchet A, Appel J, Kjaergaard N and Polzik ES (2009), "Squeezing of atomic quantum projection noise", Journal Of Modern Optics., June, 2009. Vol. 56(18-19), pp. 1993-1998. Taylor & Francis.
Abstract: We provide a framework for understanding recent experiments on squeezing of a collective atomic pseudo-spin, induced by a homodyne measurement on off-resonant probe light interrogating the atoms. The detection of light decimates the atomic state distribution and we discuss the conditions under which the resulting reduced quantum fluctuations are metrologically relevant. In particular, we consider a dual probe scheme which benefits from a cancelation of classical common mode noise sources such that quantum fluctuations from light and atoms are the main contributions to the detected signal.
BibTeX:
@article{Windpassinger2009, author = {Windpassinger, P. J. and Oblak, D. and Busk Hoff, U. and Louchet,
                    A. and Appel, J. and Kjaergaard, N. and Polzik, E. S.}, title = {Squeezing of atomic quantum projection
                    noise}, journal = {Journal Of Modern Optics}, publisher = {Taylor & Francis}, year = {2009}, month
                    = {June}, volume = {56}, number = {18--19}, pages = {1993--1998}, doi = {10.1080/09500340903033682},
                    eprint = {0906.2572} }
Windpassinger PJ, Kubasik M, Koschorreck M, Boisen A, Kjærgaard N, Polzik ES and Müller JH (2009), "Ultra low-noise differential ac-coupled photodetector for sensitive pulse detection applications", Measurement Science and Technology., May, 2009. Vol. 20(5), pp. 055301-+.
Abstract: We report on the performance of ultra low-noise differential photodetectors especially designed for probing of atomic ensembles with weak light pulses. The working principle of the detectors is described together with the analysis procedures employed to extract the photon shot noise of light pulses with ~1 μs duration. As opposed to frequency response peaked detectors, our approach allows for broadband quantum noise measurements. The equivalent noise charge (ENC) for two different hardware approaches is evaluated to 280 and 340 electrons per pulse, respectively, which corresponds to a dark noise equivalent photon number of n3dB = 0.8 × 105 and n3dB = 1.2 × 105 in the two approaches. Finally, we discuss the possibility of removing classical correlations in the output signal caused by detector imperfection by using double-correlated sampling methods.
BibTeX:
@article{Windpassinger2009a, author = {Windpassinger, P.~J. and Kubasik, M. and Koschorreck, M. and
                    Boisen, A. and Kjærgaard, N. and Polzik, E.~S. and Müller, J.~H.}, title = {Ultra low-noise
                    differential ac-coupled photodetector for sensitive pulse detection applications}, journal = {Measurement
                    Science and Technology}, year = {2009}, month = {May}, volume = {20}, number = {5}, pages = {055301-+},
                    doi = {10.1088/0957-0233/20/5/055301}, eprint = {0903.3398} }
Eckert K, Romero-Isart O, Rodriguez M, Lewenstein M, Polzik ES and Sanpera A (2008), "Quantum non-demolition detection of strongly correlated systems", Nature Physics., January, 2008. Vol. 4, pp. 50-54.
Abstract: Preparation, manipulation and detection of strongly correlated states of quantum many-body systems are among the most important goals and challenges of modern physics. Ultracold atoms offer an unprecedented playground for the realization of these goals. Here, we propose a method for detecting strongly correlated states of ultracold atoms in a quantum non-demolition scheme, that is, in the fundamentally least destructive way permitted by quantum mechanics. In our method, spatially resolved components of atomic spins couple to quantum polarization degrees of freedom of light. In this way, quantum correlations of matter are faithfully mapped on those of light; the latter can then be efficiently measured using homodyne detection. We illustrate the power of such spatially resolved quantum-noise-limited polarization measurement by applying this method to the detection of various standard and `exotic' types of antiferromagnetic order in lattice systems, and by indicating the feasibility of detection of superfluid order in Fermi liquids.
BibTeX:
@article{Eckert2008, author = {Eckert, K. and Romero-Isart, O. and Rodriguez, M. and Lewenstein, M.
                    and Polzik, E.~S. and Sanpera, A.}, title = {Quantum non-demolition detection of strongly correlated
                    systems}, journal = {Nature Physics}, year = {2008}, month = {January}, volume = {4}, pages = {50--54},
                    doi = {10.1038/nphys776}, eprint = {0709.0527} }
Fernholz T, Krauter H, Jensen K, Sherson JF, Sørensen AS and Polzik ES (2008), "Spin Squeezing of Atomic Ensembles via Nuclear-Electronic Spin Entanglement", Phys. Rev. Lett.., August, 2008. Vol. 101(7), pp. 073601. APS.
Abstract: We demonstrate spin squeezing in a room temperature ensemble of [approximate]1012 cesium atoms using their internal structure, where the necessary entanglement is created between nuclear and electronic spins of each individual atom. This state provides improvement in measurement sensitivity beyond the standard quantum limit for quantum memory experiments and applications in quantum metrology and is thus a complementary alternative to spin squeezing obtained via interatom entanglement. Squeezing of the collective spin is verified by quantum state tomography.
BibTeX:
@article{Fernholz2008, author = {T. Fernholz and H. Krauter and K. Jensen and J. F. Sherson and A. S.
                    Sørensen and E. S. Polzik}, title = {Spin Squeezing of Atomic Ensembles via Nuclear-Electronic
                    Spin Entanglement}, journal = {Phys. Rev. Lett.}, publisher = {APS}, year = {2008}, month = {August},
                    volume = {101}, number = {7}, pages = {073601}, doi = {10.1103/PhysRevLett.101.073601} }
Hilliard A, Kaminski F, Le Targat R, Olausson C, Polzik ES and Müller JH (2008), "Rayleigh superradiance and dynamic Bragg gratings in an end-pumped Bose-Einstein condensate", Physical Review A., November, 2008. Vol. 78(5), pp. 051403-+.
Abstract: We study superradiant Rayleigh scattering from a Bose-Einstein condensate (BEC) in a parameter regime where pump depletion and the exchange of photons between the end-fire modes are important. Through experiments and simulations, we show that collective atom-light coupling leads to the self-organized formation of dynamic Bragg gratings within the sample. These gratings lead to an efficient backscattering of pump photons and optical resonator structures within the BEC.
BibTeX:
@article{Hilliard2008a, author = {Hilliard, A. and Kaminski, F. and Le Targat, R. and Olausson, C. and
                    Polzik, E.~S. and Müller, J.~H.}, title = {Rayleigh superradiance and dynamic Bragg gratings in
                    an end-pumped Bose-Einstein condensate}, journal = {Physical Review A}, year = {2008}, month = {November},
                    volume = {78}, number = {5}, pages = {051403-+}, doi = {10.1103/PhysRevA.78.051403}, eprint = {0810.5690}
                    }
Krauter H, Sherson JF, Jensen K, Fernholz T, Neergaard-Nielsen JS, Nielsen BM, Oblak D, Windpassinger P, Kjærgaard N, Hilliard AJ, Olausson C, Müller JH and Polzik ES (2008), "Quantum Interface between Light and Atomic Ensembles", In Laser Spectroscopy. Singapore (XVIII), pp. 113-124. World Scientific Publishing.
BibTeX:
@inproceedings{Krauter2007, author = {H. Krauter and J.~F. Sherson and K. Jensen and T. Fernholz and
                    J.~S. Neergaard-Nielsen and B.~M. Nielsen and D. Oblak and P. Windpassinger and N. Kjærgaard and
                    A.~J. Hilliard and C. Olausson and J.~H. Müller and E.~S. Polzik}, editor = {Leo Hollberg, Jim Bergquist,
                    Mark Kasevich}, title = {Quantum Interface between Light and Atomic Ensembles}, booktitle = {Laser Spectroscopy},
                    publisher = {World Scientific Publishing}, year = {2008}, number = {XVIII}, pages = {113--124}, series
                    = {Proceedings of the XVIII International Conference on ICOLS-07}, url = {http://www.worldscibooks.com/physics/6818.html}
                    }
Muschik CA, Polzik ES and Cirac JI (2008), "Detecting entanglement in two mode squeezed states by particle counting", ArXiv e-prints., June, 2008.
Abstract: We present an entanglement criterion for two mode squeezed states which relies on particle counting only. The proposed inequality is optimal for the state under consideration and robust against particle losses up to 2/3. As it does not involve measurements of quadratures - which is typically very challenging for atomic modes - it renders the detection of atomic many-particle entanglement feasible in many different settings. Moreover it bridges the gap between entanglement verification for a qubit and criteria for continuous variables measured by homodyne detection. We illustrate its application in the context of superradiant light scattering from Bose Einstein condensates by considering the creation of entanglement between atoms and light as well as between two condensates in different momentum states. The latter scheme takes advantage of leaving the Gaussian realm and features probabilistic entanglement distillation.
BibTeX:
@article{Muschik2008, author = {Muschik, C.~A. and Polzik, E.~S. and Cirac, J.~I.}, title = {Detecting
                    entanglement in two mode squeezed states by particle counting}, journal = {ArXiv e-prints}, year = {2008},
                    month = {June}, eprint = {0806.3448} }
Oblak D, Appel J, Windpassinger PJ, Busk Hoff U, Kjærgaard N and Polzik ES (2008), "Echo spectroscopy of atomic dynamics in a Gaussian trap via phase imprints", European Physical Journal D., November, 2008. Vol. 50, pp. 67-73.
Abstract: We report on the collapse and revival of Ramsey fringe visibility when a spatially dependent phase is imprinted in the coherences of a trapped ensemble of two-level atoms. The phase is imprinted via the light shift from a Gaussian laser beam which couples the dynamics of internal and external degrees of freedom for the atoms in an echo spectroscopy sequence. The observed revivals are directly linked to the oscillatory motion of atoms in the trap. An understanding of the effect is important for quantum state engineering of trapped atoms.
BibTeX:
@article{Oblak2008, author = {Oblak, D. and Appel, J. and Windpassinger, P.~J. and Busk Hoff, U. and
                    Kjærgaard, N. and Polzik, E.~S.}, title = {Echo spectroscopy of atomic dynamics in a Gaussian trap
                    via phase imprints}, journal = {European Physical Journal D}, year = {2008}, month = {November}, volume
                    = {50}, pages = {67--73}, doi = {10.1140/epjd/e2008-00192-1}, eprint = {0807.0254} }
Owari M, Plenio MB, Polzik ES, Serafini A and Wolf MM (2008), "Squeezing the limit: quantum benchmarks for the teleportation and storage of squeezed states", New Journal of Physics., November, 2008. Vol. 10(11), pp. 113014-+.
Abstract: We derive fidelity benchmarks for the quantum storage and teleportation of squeezed states of continuous variable systems, for input ensembles where the degree of squeezing s is fixed, no information about its orientation in phase space is given, and the distribution of phase-space displacements is a Gaussian. In the limit where the latter becomes flat, we prove analytically that the maximal classical achievable fidelity (which is 1/2 without squeezing, for s=1) is given by s/(1+s) , vanishing when the degree of squeezing diverges. For mixed states, as well as for general distributions of displacements, we reduce the determination of the benchmarks to the solution of a finite-dimensional semidefinite program, which yields accurate, certifiable bounds thanks to a rigorous analysis of the truncation error. This approach may be easily adapted to more general ensembles of input states.
BibTeX:
@article{Owari2008, author = {Owari, M. and Plenio, M.~B. and Polzik, E.~S. and Serafini, A. and Wolf,
                    M.~M.}, title = {Squeezing the limit: quantum benchmarks for the teleportation and storage of squeezed
                    states}, journal = {New Journal of Physics}, year = {2008}, month = {November}, volume = {10}, number
                    = {11}, pages = {113014-+}, doi = {10.1088/1367-2630/10/11/113014}, eprint = {0808.2260} }
Polzik ES (2008), "Quantum physics: The squeeze goes on", Nature., May, 2008. Vol. 453, pp. 45-46.
Abstract: After 20 years of hard labour, squeezed states - light and matter whose quantum fluctuations have been arduously suppressed below standard levels of quantum noise - are coming of age and are ripe for application.
BibTeX:
@article{Polzik2008, author = {Polzik, E.~S.}, title = {Quantum physics: The squeeze goes on}, journal
                    = {Nature}, year = {2008}, month = {May}, volume = {453}, pages = {45--46}, doi = {10.1038/453045a} }
Vasilyev DV, Sokolov IV and Polzik ES (2008), "Quantum memory for images: A quantum hologram", Physical Review A., February, 2008. Vol. 77(2), pp. 020302-+.
Abstract: Matter-light quantum interface and quantum memory for light are important ingredients of quantum information protocols, such as quantum networks, distributed quantum computation, etc. [P. Zoller , Eur. Phys. J. D 36, 203 (2005)]. In this paper we present a spatially multimode scheme for quantum memory for light, which we call a quantum hologram. Our approach uses a multiatom ensemble which has been shown to be efficient for a single spatial mode quantum memory. Due to the multiatom nature of the ensemble and to the optical parallelism it is capable of storing many spatial modes, a feature critical for the present proposal. A quantum hologram with the fidelity exceeding that of classical hologram will be able to store quantum features of an image, such as multimode superposition and entangled quantum states, something that a standard hologram is unable to achieve.
BibTeX:
@article{Vasilyev2008, author = {Vasilyev, D.~V. and Sokolov, I.~V. and Polzik, E.~S.}, title = {Quantum
                    memory for images: A quantum hologram}, journal = {Physical Review A}, year = {2008}, month = {February},
                    volume = {77}, number = {2}, pages = {020302-+}, doi = {10.1103/PhysRevA.77.020302}, eprint = {0704.1737}
                    }
Windpassinger PJ, Oblak D, Petrov PG, Kubasik M, Saffman M, Alzar CLG, Appel J, Müller JH, Kjærgaard N and Polzik ES (2008), "Nondestructive Probing of Rabi Oscillations on the Cesium Clock Transition near the Standard Quantum Limit", Physical Review Letters., March, 2008. Vol. 100(10), pp. 103601-+.
Abstract: We report on the nondestructive observation of Rabi oscillations on the Cs clock transition. The internal atomic state evolution of a dipole-trapped ensemble of cold atoms is inferred from the phase shift of a probe laser beam as measured using a Mach-Zehnder interferometer. We describe a single color as well as a two-color probing scheme. Using the latter, measurements of the collective pseudospin projection of atoms in a superposition of the clock states are performed and the observed spin fluctuations are shown to be close to the standard quantum limit.
Review: I
BibTeX:
@article{Windpassinger2008, author = {Windpassinger, P.~J. and Oblak, D. and Petrov, P.~G. and Kubasik,
                    M. and Saffman, M. and Alzar, C.~L.~G. and Appel, J. and Müller, J.~H. and Kjærgaard, N. and
                    Polzik, E.~S.}, title = {Nondestructive Probing of Rabi Oscillations on the Cesium Clock Transition near
                    the Standard Quantum Limit}, journal = {Physical Review Letters}, year = {2008}, month = {March}, volume
                    = {100}, number = {10}, pages = {103601-+}, doi = {10.1103/PhysRevLett.100.103601}, eprint = {0801.4126}
                    }
Windpassinger PJ, Oblak D, Busk Hoff U, Appel J, Kjærgaard N and Polzik ES (2008), "Inhomogeneous light shift effects on atomic quantum state evolution in non-destructive measurements", New. J. Phys.., May, 2008. Vol. 10(5), pp. 053032-+.
Abstract: Various parameters of a trapped collection of cold and ultracold atoms can be determined non-destructively by measuring the phase shift of an off-resonant probe beam, caused by the state-dependent index of refraction of the atoms. The dispersive light atom interaction, however, gives rise to a differential light shift (ac Stark shift) between the atomic states which, for a non-uniform probe intensity distribution, causes an inhomogeneous dephasing between the atoms. In this paper, we investigate the effects of this inhomogeneous light shift in non-destructive measurement schemes in cold caesium. We interpret our experimental data on dispersively probed Rabi oscillations and Ramsey fringes in terms of a simple light shift model which is shown to describe the observed behavior well. Furthermore, we show that by using spin echo techniques, the inhomogeneous phase shift distribution between the two clock levels can be reversed.
BibTeX:
@article{Windpassinger2008a, author = {Windpassinger, P.~J. and Oblak, D. and Busk Hoff, U. and Appel,
                    J. and Kjærgaard, N. and Polzik, E.~S.}, title = {Inhomogeneous light shift effects on atomic quantum
                    state evolution in non-destructive measurements}, journal = {New. J. Phys.}, year = {2008}, month = {May},
                    volume = {10}, number = {5}, pages = {053032-+}, doi = {10.1088/1367-2630/10/5/053032}, eprint = {0801.3242}
                    }
Eckert K, Zawitkowski Ł, Sanpera A, Lewenstein M and Polzik ES (2007), "Quantum Polarization Spectroscopy of Ultracold Spinor Gases", Physical Review Letters., March, 2007. Vol. 98(10), pp. 100404-+.
Abstract: We propose a method for the detection of ground state quantum phases of spinor gases through a series of two quantum nondemolition measurements performed by sending off-resonant, polarized light pulses through the gas. Signatures of various mean-field as well as strongly correlated phases of F=1 and F=2 spinor gases obtained by detecting quantum fluctuations and mean values of polarization of transmitted light are identified.
BibTeX:
@article{Eckert2007, author = {Eckert, K. and Zawitkowski, Ł. and Sanpera, A. and Lewenstein, M. and
                    Polzik, E.~S.}, title = {Quantum Polarization Spectroscopy of Ultracold Spinor Gases}, journal = {Physical
                    Review Letters}, year = {2007}, month = {March}, volume = {98}, number = {10}, pages = {100404-+}, doi
                    = {10.1103/PhysRevLett.98.100404}, eprint = {cond-mat/0608306} }
Mishina OS, Kupriyanov DV, Müller JH and Polzik ES (2007), "Spectral theory of quantum memory and entanglement via Raman scattering of light by an atomic ensemble", Physical Review A., April, 2007. Vol. 75(4), pp. 042326-+.
Abstract: We discuss theoretically quantum interface between light and a spin polarized ensemble of atoms with the spin ⩾1 based on an off-resonant Raman scattering. We present the spectral theory of the light atom interaction and show how particular spectral modes of quantum light couple to spatial modes of the extended atomic ensemble. We show how this interaction can be used for quantum memory storage and retrieval and for deterministic entanglement protocols. The proposed protocols are attractive due to their simplicity since they involve just a single pass of light through atoms without the need for elaborate pulse shaping or quantum feedback. As a practically relevant example we consider the interaction of a light pulse with hyperfine components of D1 line of Rb87 . The quality of the proposed protocols is verified via analytical and numerical analysis.
BibTeX:
@article{Mishina2007, author = {Mishina, O.~S. and Kupriyanov, D.~V. and Müller, J.~H. and Polzik,
                    E.~S.}, title = {Spectral theory of quantum memory and entanglement via Raman scattering of light by
                    an atomic ensemble}, journal = {Physical Review A}, year = {2007}, month = {April}, volume = {75}, number
                    = {4}, pages = {042326-+}, doi = {10.1103/PhysRevA.75.042326}, eprint = {quant-ph/0611228} }
Neergaard-Nielsen JS, Nielsen BM, Takahashi H, Vistnes AI and Polzik ES (2007), "High purity bright single photon source", Optics Express., June, 2007. Vol. 15, pp. 7940-7949.
Abstract: Using cavity-enhanced non-degenerate parametric down-conversion, we have built a frequency tunable source of heralded single photons with a narrow bandwidth of 8 MHz, making it compatible with atomic quantum memories. The photon state is $70 pure single photon as characterized by a tomographic measurement and reconstruction of the quantum state, revealing a clearly negative Wigner function. Furthermore, it has a spectral brightness of ~1,500 photons/s per MHz bandwidth, making it one of the brightest single photon sources available. We also investigate the correlation function of the down-converted fields using a combination of two very distinct detection methods; photon counting and homodyne measurement.
BibTeX:
@article{Neergaard-Nielsen2007, author = {Neergaard-Nielsen, J.~S. and Nielsen, B.~M. and Takahashi,
                    H. and Vistnes, A.~I. and Polzik, E.~S.}, title = {High purity bright single photon source}, journal
                    = {Optics Express}, year = {2007}, month = {June}, volume = {15}, pages = {7940--7949}, doi = {10.1364/OE.15.007940},
                    eprint = {0704.1864} }
Petrov PG, Oblak D, Alzar CLG, Kjærgaard N and Polzik ES (2007), "Nondestructive interferometric characterization of an optical dipole trap", Physical Review A., March, 2007. Vol. 75(3), pp. 033803-+.
Abstract: A method for nondestructive characterization of a dipole-trapped atomic sample is presented. It relies on a measurement of the phase shift imposed by cold atoms on an optical pulse that propagates through a free-space Mach-Zehnder interferometer. Using this technique we are able to determine, with very good accuracy, relevant trap parameters such as the atomic sample temperature, trap oscillation frequencies, and loss rates. Another important feature is that our method is faster than conventional absorption or fluorescence techniques, allowing the combination of high-dynamical range measurements and a reduced number of spontaneous emission events per atom.
BibTeX:
@article{Petrov2007, author = {Petrov, P.~G. and Oblak, D. and Alzar, C.~L.~G. and Kjærgaard,
                    N. and Polzik, E.~S.}, title = {Nondestructive interferometric characterization of an optical dipole
                    trap}, journal = {Physical Review A}, year = {2007}, month = {March}, volume = {75}, number = {3}, pages
                    = {033803-+}, doi = {10.1103/PhysRevA.75.033803}, eprint = {quant-ph/0610107} }
Fiurášek J, Sherson J, Opatrný T and Polzik ES (2006), "Single-passage readout of atomic quantum memory", Physical Review A., February, 2006. Vol. 73(2), pp. 022331-+.
Abstract: A scheme for retrieving quantum information stored in collective atomic spin systems onto optical pulses is presented. Two off-resonant light pulses cross the atomic medium in two orthogonal directions and are interferometrically recombined in such a way that one of the outputs carries most of the information stored in the medium. In contrast to previous schemes our approach requires neither multiple passes through the medium nor feedback on the light after passing the sample, which makes the scheme very efficient. The price for that is some added noise which is, however, small enough for the method to beat the classical limits.
BibTeX:
@article{Fiurasek2006, author = {Fiurášek, J. and Sherson, J. and Opatrný, T. and
                    Polzik, E.~S.}, title = {Single-passage readout of atomic quantum memory}, journal = {Physical Review
                    A}, year = {2006}, month = {February}, volume = {73}, number = {2}, pages = {022331-+}, doi = {10.1103/PhysRevA.73.022331},
                    eprint = {quant-ph/0510099} }
Hammerer K, Polzik ES and Cirac JI (2006), "High-fidelity teleportation between light and atoms", Physical Review A. Vol. 74(6), pp. 064301. APS.
Abstract: We show how high-fidelity quantum teleportation of light to atoms can be achieved in the same setup as was used in the recent experiment [J. Sherson et al., Nature 443, 557, 2006], where such an interspecies quantum state transfer was demonstrated for the first time. Our improved protocol takes advantage of the rich multimode entangled structure of the state of atoms and scattered light and requires simple postprocessing of homodyne detection signals and squeezed light in order to achieve fidelities up to 90% (85 for teleportation of coherent (qubit) states under realistic experimental conditions. The remaining limitation is due to atomic decoherence and light losses.
BibTeX:
@article{Hammerer2006, author = {K. Hammerer and E. S. Polzik and J. I. Cirac}, title = {High-fidelity
                    teleportation between light and atoms}, journal = {Physical Review A}, publisher = {APS}, year = {2006},
                    volume = {74}, number = {6}, pages = {064301}, doi = {10.1103/PhysRevA.74.064301} }
Mishina O, Polzik E and Kupriyanov D (2006), "Macroscopic quantum information channel via the polarization-sensitive interaction between the light and spin subsystems", In Quantum information processing from theory to experiment. Amsterdam Vol. 199, pp. 346-352. IOS Press.
BibTeX:
@inproceedings{Mishina2006, author = {Oksana Mishina and Eugene Polzik and Dmitriy Kupriyanov}, editor
                    = {Dimitris G. Angelakis and Matthias Christandl and Artur Ekert and Alastair Kay and Sergei Kulik},
                    title = {Macroscopic quantum information channel via the polarization-sensitive interaction between the
                    light and spin subsystems}, booktitle = {Quantum information processing from theory to experiment}, publisher
                    = {IOS Press}, year = {2006}, volume = {199}, pages = {346--352}, series = {NATO science series. Series
                    III, Computer and systems sciences}, note = {ISBN 978-1-58603-611-9}, url = {http://booksonline.iospress.nl/Content/View.aspx?piid=2634},
                    eprint = {quant-ph/0509220} }
Muschik CA, Hammerer K, Polzik ES and Cirac JI (2006), "Efficient quantum memory and entanglement between light and an atomic ensemble using magnetic fields", Physical Review A., June, 2006. Vol. 73(6), pp. 062329-+.
Abstract: We present two protocols, one for the storage of light in an atomic ensemble and the subsequent retrieval, and another one for the generation of entanglement between light and atoms. They rely on two passes of a single pulse through the ensemble, Larmor precessing in an external field. Both protocols work deterministically and the relevant figures of merit—such as the fidelity or the EPR variance—scale exponentially in the coupling strength. We solve the corresponding Maxwell-Bloch equations describing the scattering process and determine the resulting input-output relations which only involve one relevant light mode that, in turn, can be easily accessed experimentally.
BibTeX:
@article{Muschik2006, author = {Muschik, C.~A. and Hammerer, K. and Polzik, E.~S. and Cirac, J.~I.},
                    title = {Efficient quantum memory and entanglement between light and an atomic ensemble using magnetic
                    fields}, journal = {Physical Review A}, year = {2006}, month = {June}, volume = {73}, number = {6}, pages
                    = {062329-+}, doi = {10.1103/PhysRevA.73.062329}, eprint = {quant-ph/0512226} }
Neergaard-Nielsen JS, Nielsen BM, Hettich C, Mølmer K and Polzik ES (2006), "Generation of a Superposition of Odd Photon Number States for Quantum Information Networks", Phys. Rev. Lett.., August, 2006. Vol. 97(8), pp. 083604. APS.
Abstract: We report on the experimental observation of quantum-network-compatible light described by a nonpositive Wigner function. The state is generated by photon subtraction from a squeezed vacuum state produced by a continuous wave optical parametric amplifier. Ideally, the state is a coherent superposition of odd photon number states, closely resembling a superposition of weak coherent states |alpha>-|-alpha>. In the limit of low squeezing the state is basically a single photon state. Light is generated with about 10 000 and more events per second in a nearly perfect spatial mode with a Fourier-limited frequency bandwidth which matches well atomic quantum memory requirements. The generated state of light is an excellent input state for testing quantum memories, quantum repeaters, and linear optics quantum computers.
BibTeX:
@article{Neergaard-Nielsen2006, author = {J. S. Neergaard-Nielsen and B. Melholt Nielsen and C. Hettich
                    and K. Mølmer and E. S. Polzik}, title = {Generation of a Superposition of Odd Photon Number States
                    for Quantum Information Networks}, journal = {Phys. Rev. Lett.}, publisher = {APS}, year = {2006}, month
                    = {August}, volume = {97}, number = {8}, pages = {083604}, doi = {10.1103/PhysRevLett.97.083604} }
Sherson JF, Krauter H, Olsson RK, Julsgaard B, Hammerer K, Cirac I and Polzik ES (2006), "Quantum teleportation between light and matter", Nature. Vol. 443, pp. 557-560.
Abstract: Quantum teleportation1 is an important ingredient in distributed quantum networks2, and can also serve as an elementary operation in quantum computers3. Teleportation was first demonstrated as a transfer of a quantum state of light onto another light beam4, 5, 6; later developments used optical relays7 and demonstrated entanglement swapping for continuous variables8. The teleportation of a quantum state between two single material particles (trapped ions) has now also been achieved9, 10. Here we demonstrate teleportation between objects of a different nature—light and matter, which respectively represent 'flying' and 'stationary' media. A quantum state encoded in a light pulse is teleported onto a macroscopic object (an atomic ensemble containing 1012 caesium atoms). Deterministic teleportation is achieved for sets of coherent states with mean photon number (n) up to a few hundred. The fidelities are 0.58 plusminus 0.02 for n = 20 and 0.60 plusminus 0.02 for n = 5—higher than any classical state transfer can possibly achieve11. Besides being of fundamental interest, teleportation using a macroscopic atomic ensemble is relevant for the practical implementation of a quantum repeater2. An important factor for the implementation of quantum networks is the teleportation distance between transmitter and receiver; this is 0.5 metres in the present experiment. As our experiment uses propagating light to achieve the entanglement of light and atoms required for teleportation, the present approach should be scalable to longer distances.
BibTeX:
@article{Sherson2006, author = {Jacob F. Sherson and Hanna Krauter and Rasmus K. Olsson and Brian Julsgaard
                    and Klemens Hammerer and Ignacio Cirac and Eugene S. Polzik}, title = {Quantum teleportation between
                    light and matter}, journal = {Nature}, year = {2006}, volume = {443}, pages = {557--560}, doi = {10.1038/nature05136}
                    }
Sherson J, Julsgaard B and Polzik ES (2006), "Deterministic Atom-Light Quantum Interface", In Advances In Atomic, Molecular, and Optical Physics. Vol. 54, pp. 81-130. Academic Press.
Abstract: The notion of an atom-light quantum interface has been developed in the past decade, to a large extent due to demands within the new field of quantum information processing and communication. A promising type of such interface using large atomic ensembles has emerged in the past several years. In this chapter we review this area of research with a special emphasis on deterministic high fidelity quantum information protocols. Two recent experiments, entanglement of distant atomic objects and quantum memory for light are described in detail.
BibTeX:
@incollection{Sherson2006a, author = {Jacob Sherson and Brian Julsgaard and Eugene S. Polzik}, editor
                    = {P.R. Berman, C.C. Lin and E. Arimondo}, title = {Deterministic Atom-Light Quantum Interface}, booktitle
                    = {Advances In Atomic, Molecular, and Optical Physics}, publisher = {Academic Press}, year = {2006},
                    volume = {54}, pages = {81--130}, series = {Advances In Atomic, Molecular, and Optical Physics}, doi
                    = {10.1016/S1049-250X(06)54002-9}, eprint = {quant-ph/0601186} }
Sherson J, Sørensen AS, Fiurášek J, Mølmer K and Polzik ES (2006), "Light qubit storage and retrieval using macroscopic atomic ensembles", Physical Review A., July, 2006. Vol. 74(1), pp. 011802-+.
Abstract: We present an experimentally feasible protocol for the complete storage and retrieval of arbitrary light states in an atomic quantum memory using the Faraday interaction between light and matter. Our protocol relies on multiple passages of a single light pulse through the atomic ensemble without the impractical requirement of kilometer-long delay lines between the passages. A time-dependent interaction strength enables the storage and retrieval of states with arbitrary pulse shapes. The fidelity approaches unity exponentially without squeezed or entangled initial states, as illustrated by calculations for a photonic qubit.
BibTeX:
@article{Sherson2006b, author = {Sherson, J. and Sørensen, A.~S. and Fiurášek,
                    J. and Mølmer, K. and Polzik, E.~S.}, title = {Light qubit storage and retrieval using macroscopic
                    atomic ensembles}, journal = {Physical Review A}, year = {2006}, month = {July}, volume = {74}, number
                    = {1}, pages = {011802-+}, doi = {10.1103/PhysRevA.74.011802}, eprint = {quant-ph/0505170} }
de Echaniz SR, Mitchell MW, Kubasik M, Koschorreck M, Crepaz H, Eschner J and Polzik ES (2005), "Conditions for spin squeezing in a cold^87Rb ensemble", Journal of Optics B: Quantum and Semiclassical Optics., December, 2005. Vol. 7, pp. 548-+.
Abstract: We study the conditions for generating spin squeezing via a quantum non-demolition measurement in an ensemble of cold87Rb atoms. By considering the interaction of atoms in the 5S1/2(F = 1) ground state with probe light tuned near the D2 transition, we show that, for large detunings, this system is equivalent to a spin-1/2 system when suitable Zeeman substates and quantum operators are used to define a pseudo-spin. The degree of squeezing is derived for the rubidium system in the presence of scattering causing decoherence and loss. We describe how the system can decohere and lose atoms, and predict as much as $75 spin squeezing for atomic densities typical of optical dipole traps.
BibTeX:
@article{Echaniz2005, author = {de Echaniz, S.~R. and Mitchell, M.~W. and Kubasik, M. and Koschorreck,
                    M. and Crepaz, H. and Eschner, J. and Polzik, E.~S.}, title = {Conditions for spin squeezing in a cold^87Rb
                    ensemble}, journal = {Journal of Optics B: Quantum and Semiclassical Optics}, year = {2005}, month =
                    {December}, volume = {7}, pages = {548-+}, doi = {10.1088/1464-4266/7/12/016}, eprint = {quant-ph/0506084}
                    }
Hammerer K, Wolf MM, Polzik ES and Cirac JI (2005), "Quantum Benchmark for Storage and Transmission of Coherent States", Physical Review Letters. Vol. 94(15), pp. 150503. American Physical Society.
Abstract: We consider the storage and transmission of a Gaussian distributed set of coherent states of continuous variable systems. We prove a limit on the average fidelity achievable when the states are transmitted or stored by a classical channel, i.e., a measure and repreparation scheme which sends or stores classical information only. The obtained bound is tight and serves as a benchmark which has to be surpassed by quantum channels in order to outperform any classical strategy. The success in experimental demonstrations of quantum memories as well as quantum teleportation has to be judged on this footing.
BibTeX:
@article{Hammerer2005, author = {Hammerer, K. and Wolf, M. M. and Polzik, E. S. and Cirac, J. I.}, title
                    = {Quantum Benchmark for Storage and Transmission of Coherent States}, journal = {Physical Review Letters},
                    publisher = {American Physical Society}, year = {2005}, volume = {94}, number = {15}, pages = {150503},
                    doi = {10.1103/PhysRevLett.94.150503} }
Hammerer K, Polzik ES and Cirac JI (2005), "Teleportation and spin squeezing utilizing multimode entanglement of light with atoms", Physical Review A., November, 2005. Vol. 72(5), pp. 052313-+.
Abstract: We present a protocol for the teleportation of the quantum state of a pulse of light onto the collective spin state of an atomic ensemble. The entangled state of light and atoms employed as a resource in this protocol is created by probing the collective atomic spin, Larmor precessing in an external magnetic field, off resonantly with a coherent pulse of light. We take here full account of the effects of Larmor precession and show that it gives rise to a qualitatively different type of multimode entangled state of light and atoms. The protocol is shown to be robust against the dominating sources of noise and can be implemented with an atomic ensemble at room temperature interacting with free-space light. We also provide a scheme to perform the readout of the Larmor precessing spin state enabling the verification of successful teleportation as well as the creation of spin squeezing.
BibTeX:
@article{Hammerer2005a, author = {Hammerer, K. and Polzik, E.~S. and Cirac, J.~I.}, title = {Teleportation
                    and spin squeezing utilizing multimode entanglement of light with atoms}, journal = {Physical Review
                    A}, year = {2005}, month = {November}, volume = {72}, number = {5}, pages = {052313-+}, doi = {10.1103/PhysRevA.72.052313},
                    eprint = {quant-ph/0511174} }
Kupriyanov DV, Mishina OS, Sokolov IM, Julsgaard B and Polzik ES (2005), "Multimode entanglement of light and atomic ensembles via off-resonant coherent forward scattering", Physical Review A., March, 2005. Vol. 71(3), pp. 032348-+.
Abstract: Quantum theoretical treatment of coherent forward scattering of light in a polarized atomic ensemble with an arbitrary angular momentum is developed. We consider coherent forward scattering of a weak radiation field interacting with a realistic multilevel atomic transition. Based on the concept of an effective Hamiltonian and on the Heisenberg formalism, we discuss the coupled dynamics of the quantum fluctuations of the polarization Stokes components of propagating light and of the collective spin fluctuations of the scattering atoms. We show that in the process of coherent forward scattering, this dynamics can be described in terms of a polariton-type spin wave created in the atomic sample. Our work presents a general example of an entangling process in the system of collective quantum states of light and atomic angular momenta, previously considered only for the case of spin- (1)/(2) atoms. We use the developed general formalism to test the applicability of the spin- (1)/(2) approximation for modeling the quantum nondemolishing measurement of atoms with a higher angular momentum.
BibTeX:
@article{Kupriyanov2005, author = {Kupriyanov, D.~V. and Mishina, O.~S. and Sokolov, I.~M. and Julsgaard,
                    B. and Polzik, E.~S.}, title = {Multimode entanglement of light and atomic ensembles via off-resonant
                    coherent forward scattering}, journal = {Physical Review A}, year = {2005}, month = {March}, volume =
                    {71}, number = {3}, pages = {032348-+}, doi = {10.1103/PhysRevA.71.032348}, eprint = {quant-ph/0411083}
                    }
Müller JH, Petrov P, Oblak D, Garrido Alzar CL, de Echaniz SR and Polzik ES (2005), "Diffraction effects on light-atomic-ensemble quantum interface", Phys. Rev. A., March, 2005. Vol. 71(3), pp. 033803-+.
Abstract: We present a simple method to include the effects of diffraction into the description of a light-atomic ensemble quantum interface in the context of collective variables. Carrying out a scattering calculation we single out the purely geometrical effect and apply our method to the experimental relevant case of Gaussian-shaped atomic samples stored in single beam optical dipole traps probed by a Gaussian beam. We derive simple scaling relations for the effect of the interaction geometry and compare our findings to the results from one-dimensional models of light propagation.
BibTeX:
@article{Muller2005, author = {Müller, J.~H. and Petrov, P. and Oblak, D. and Garrido Alzar, C.~L.
                    and de Echaniz, S.~R. and Polzik, E.~S.}, title = {Diffraction effects on light-atomic-ensemble quantum
                    interface}, journal = {Phys. Rev. A}, year = {2005}, month = {March}, volume = {71}, number = {3}, pages
                    = {033803-+}, doi = {10.1103/PhysRevA.71.033803}, eprint = {physics/0403138} }
Oblak D, Petrov PG, Garrido Alzar CL, Tittel W, Vershovski AK, Mikkelsen JK, Sørensen JL and Polzik ES (2005), "Quantum-noise-limited interferometric measurement of atomic noise: Towards spin squeezing on the Cs clock transition", Physical Review A., April, 2005. Vol. 71(4), pp. 043807-+.
Abstract: We investigate theoretically and experimentally a nondestructive interferometric measurement of the state population of an ensemble of laser-cooled and trapped atoms. This study is a step toward generation of (pseudo)spin squeezing of cold atoms targeted at the improvement of the cesium clock performance beyond the limit set by the quantum projection noise of atoms. We calculate the phase shift and the quantum noise of a near-resonant optical probe pulse propagating through a cloud of cold Cs133 atoms. We analyze the figure of merit for a quantum nondemolition (QND) measurement of the collective pseudospin and show that it can be expressed simply as a product of the ensemble optical density and the pulse-integrated rate of the spontaneous emission caused by the off-resonant probe light. Based on this, we propose a protocol for the sequence of operations required to generate and utilize spin squeezing for the improved atomic clock performance via a QND measurement on the probe light. In the experimental part we demonstrate that the interferometric measurement of the atomic population can reach a sensitivity of the order of Nat in a cloud of Nat cold atoms, which is an important benchmark toward the experimental realization of the theoretically analyzed protocol.
BibTeX:
@article{Oblak2005, author = {Oblak, D. and Petrov, P.~G. and Garrido Alzar, C.~L. and Tittel, W. and
                    Vershovski, A.~K. and Mikkelsen, J.~K. and Sørensen, J.~L. and Polzik, E.~S.}, title = {Quantum-noise-limited
                    interferometric measurement of atomic noise: Towards spin squeezing on the Cs clock transition}, journal
                    = {Physical Review A}, year = {2005}, month = {April}, volume = {71}, number = {4}, pages = {043807-+},
                    doi = {10.1103/PhysRevA.71.043807} }
Polzik E and Fiurášek J (2005), "Quantum interface between light and atomic ensembles", In Lectures on Quantum Information. , pp. 515-534. Wiley-VCH.
BibTeX:
@incollection{Polzik2005, author = {Polzik, E.S. and Fiurášek, J}, editor = {Dagmar Bruß
                    and Gerd Leuchs}, title = {Quantum interface between light and atomic ensembles}, booktitle = {Lectures
                    on Quantum Information}, publisher = {Wiley-VCH}, year = {2005}, pages = {515--534} }
Sherson J, Julsgaard B and Polzik E (2005), "Distant entanglement of macroscopic gas samples", Decoherence, Entanglement and Information Protection in Complex Quantum Systems., In Decoherence, Entanglement and Information Protection in Complex Quantum Systems. Klüwer, Amsterdam Vol. 189(V), pp. 353-372. Springer.
Abstract: One of the main ingredients in most quantum information protocols is a reliable source of two entangled systems. Such systems have been generated experimentally several years ago for light but has only in the past few years been demonstrated for atomic systems. None of these approaches however involve two atomic systems situated in separate environments. This is necessary for the creation of entanglement over arbitrary distances which is required for many quantum information protocols such as atomic teleportation. We present an experimental realization of such distant entanglement based on an adaptation of the entanglement of macroscopic gas samples containing about 10^11 cesium atoms shown previously by our group. The entanglement is generated via the off-resonant Kerr interaction between the atomic samples and a pulse of light. The achieved entanglement distance is 0.35m but can be scaled arbitrarily. The feasibility of an implementation of various quantum information protocols using macroscopic samples of atoms has therefore been greatly increased. We also present a theoretical modeling in terms of canonical position and momentum operators X and P describing the entanglement generation and verification in presence of decoherence mechanisms.
BibTeX:
@incollection{Sherson2005, author = {Sherson, J. and Julsgaard, B. and Polzik, E.}, editor = {V.M. Akulin
                    and A. Sarfati and G. Kurizki and S. Pellegrin}, title = {Distant entanglement of macroscopic gas samples},
                    booktitle = {Decoherence, Entanglement and Information Protection in Complex Quantum Systems}, journal
                    = {Decoherence, Entanglement and Information Protection in Complex Quantum Systems}, publisher = {Springer},
                    year = {2005}, volume = {189}, number = {V}, pages = {353--372}, series = {Decoherence, Entanglement
                    and Information Protection in Complex Quantum SystemsDecoherence, Entanglement and Information Protection
                    in Complex Quantum Systems
Proceedings of the NATO ARW on Decoherence}, doi = {10.1007/1-4020-3283-8_24}, eprint = {quant-ph/0408146} }
Zoller P, Beth T, Binosi D, Blatt R, Briegel H, Bruss D, Calarco T, Cirac JI, Deutsch D, Eisert J, Ekert A, Fabre C, Gisin N, Grangiere P, Grassl M, Haroche S, Imamoglu A, Karlson A, Kempe J, Kouwenhoven L, Kröll S, Leuchs G, Lewenstein M, Loss D, Lütkenhaus N, Massar S, Mooij JE, Plenio MB, Polzik E, Popescu S, Rempe G, Sergienko A, Suter D, Twamley J, Wendin G, Werner R, Winter A, Wrachtrup J and Zeilinger A (2005), "Quantum information processing and communication. Strategic report on current status, visions and goals for research in Europe", European Physical Journal D., November, 2005. Vol. 36, pp. 203-228.
Abstract: We present an excerpt of the document “Quantum Information Processing and Communication: Strategic report on current status, visions and goals for research in Europe”, which has been recently published in electronic form at the website of FET (the Future and Emerging Technologies Unit of the Directorate General Information Society of the European Commission, http://www.cordis.lu/ist/fet/qipc-sr.htm). This document has been elaborated, following a former suggestion by FET, by a committee of QIPC scientists to provide input towards the European Commission for the preparation of the Seventh Framework Program. Besides being a document addressed to policy makers and funding agencies (both at the European and national level), the document contains a detailed scientific assessment of the state-of-the-art, main research goals, challenges, strengths, weaknesses, visions and perspectives of all the most relevant QIPC sub-fields, that we report here. Dedicated to the memory of Prof. Th. Beth, one of the pioneers of QIPC, whose contributions have had a significant scientific impact on the development as well as on the visibility of a field that he enthusiastically helped to shape since its early days.
BibTeX:
@article{Zoller2005, author = {P. Zoller and T. Beth and D. Binosi and R. Blatt and H. Briegel and D.
                    Bruss and T. Calarco and J.~I. Cirac and D. Deutsch and J. Eisert and A. Ekert and C. Fabre and N. Gisin
                    and P. Grangiere and M. Grassl and S. Haroche and A. Imamoglu and A. Karlson and J. Kempe and L. Kouwenhoven
                    and S. Kröll and G. Leuchs and M. Lewenstein and D. Loss and N. Lütkenhaus and S. Massar and
                    J.~E. Mooij and M.~B. Plenio and E. Polzik and S. Popescu and G. Rempe and A. Sergienko and D. Suter
                    and J. Twamley and G. Wendin and R. Werner and A. Winter and J. Wrachtrup and A. Zeilinger}, title =
                    {Quantum information processing and communication. Strategic report on current status, visions and goals
                    for research in Europe}, journal = {European Physical Journal D}, year = {2005}, month = {November},
                    volume = {36}, pages = {203--228}, doi = {10.1140/epjd/e2005-00251-1} }
Fiurášek J, Cerf NJ and Polzik ES (2004), "Quantum Cloning of a Coherent Light State into an Atomic Quantum Memory", Physical Review Letters., October, 2004. Vol. 93(18), pp. 180501-+.
Abstract: A scheme for the optimal Gaussian cloning of coherent light states at the interface between light and atoms is proposed. The distinct feature of this proposal is that the clones are stored in an atomic quantum memory, which is important for applications in quantum communication. The atomic quantum cloning machine requires only a single passage of the light pulse through the atomic ensembles followed by the measurement of a light quadrature and an appropriate feedback, which renders the protocol experimentally feasible. An alternative protocol, where one of the clones is carried by the outgoing light pulse, is discussed in connection with eavesdropping on quantum key distribution.
BibTeX:
@article{Fiurasek2004, author = {Fiurášek, J. and Cerf, N.~J. and Polzik, E.~S.}, title
                    = {Quantum Cloning of a Coherent Light State into an Atomic Quantum Memory}, journal = {Physical Review
                    Letters}, year = {2004}, month = {October}, volume = {93}, number = {18}, pages = {180501-+}, doi = {10.1103/PhysRevLett.93.180501},
                    eprint = {quant-ph/0404054} }
Hammerer K, Mølmer K, Polzik ES and Cirac JI (2004), "Light-matter quantum interface", Physical Review A., October, 2004. Vol. 70(4), pp. 044304-+.
Abstract: We propose a quantum interface which applies multiple passes of a pulse of light through an atomic sample with phase/polarization rotations in between the passes. Our proposal does not require nonclassical light input or measurements on the system, and it predicts rapidly growing entanglement of light and atoms from just coherent inputs. The proposed interface makes it possible to achieve a number of tasks within quantum-information processing, including teleportation between light and atoms, quantum memory for light, and squeezing of atomic and light variables.
BibTeX:
@article{Hammerer2004, author = {Hammerer, K. and Mølmer, K. and Polzik, E.~S. and Cirac, J.~I.},
                    title = {Light-matter quantum interface}, journal = {Physical Review A}, year = {2004}, month = {October},
                    volume = {70}, number = {4}, pages = {044304-+}, doi = {10.1103/PhysRevA.70.044304}, eprint = {quant-ph/0312156}
                    }
Julsgaard B, Sherson J, Cirac JI, Fiurášek J and Polzik ES (2004), "Experimental demonstration of quantum memory for light", Nature. Vol. 432, pp. 482-486.
Abstract: The information carrier of today's communications, a weak pulse of light, is an intrinsically quantum object. As a consequence, complete information about the pulse cannot be perfectly recorded in a classical memory, even in principle. In the field of quantum information, this has led to the long-standing challenge of how to achieve a high-fidelity transfer of an independently prepared quantum state of light onto an atomic quantum state1, 2, 3, 4. Here we propose and experimentally demonstrate a protocol for such a quantum memory based on atomic ensembles. Recording of an externally provided quantum state of light onto the atomic quantum memory is achieved with 70 per cent fidelity, significantly higher than the limit for classical recording. Quantum storage of light is achieved in three steps: first, interaction of the input pulse and an entangling field with spin-polarized caesium atoms; second, subsequent measurement of the transmitted light; and third, feedback onto the atoms using a radio-frequency magnetic pulse conditioned on the measurement result. The density of recorded states is 33 per cent higher than the best classical recording of light onto atoms, with a quantum memory lifetime of up to 4 milliseconds.
BibTeX:
@article{Julsgaard2004, author = {Brian Julsgaard and Jacob Sherson and J. Ignacio Cirac and Jaromír
                    Fiurášek and Eugene S. Polzik}, title = {Experimental demonstration of quantum memory for
                    light}, journal = {Nature}, year = {2004}, volume = {432}, pages = {482--486}, doi = {10.1038/nature03064}
                    }
Julsgaard B, Sherson J, Sørensen JL and Polzik ES (2004), "Characterizing the spin state of an atomic ensemble using the magneto-optical resonance method", Journal of Optics B: Quantum and Semiclassical Optics., January, 2004. Vol. 6, pp. 5-14.
Abstract: Quantum information protocols utilizing atomic ensembles require preparation of a coherent spin state (CSS) of the ensemble as an important starting point. We investigate the magneto-optical resonance method for characterizing a spin state of caesium atoms in a paraffin coated vapour cell. Atoms in a constant magnetic field are subject to an off-resonant laser beam and an RF magnetic field. The spectrum of the Zeeman sub-levels, in particular the weak quadratic Zeeman effect, enables us to measure the spin orientation, the number of atoms, and the transverse spin coherence time. Notably the use of 894 nm pumping light on the D1 line, ensuring the state F = 4, mF = 4 is a dark state, helps us to achieve spin orientation of better than $98. Hence we can establish a CSS with high accuracy, which is critical for the analysis of the entangled states of atoms.
BibTeX:
@article{Julsgaard2004a, author = {Julsgaard, B. and Sherson, J. and Sørensen, J.~L. and Polzik,
                    E.~S.}, title = {Characterizing the spin state of an atomic ensemble using the magneto-optical resonance
                    method}, journal = {Journal of Optics B: Quantum and Semiclassical Optics}, year = {2004}, month = {January},
                    volume = {6}, pages = {5--14}, doi = {10.1088/1464-4266/6/1/002}, eprint = {quant-ph/0307028} }
Julsgaard B, Schori C, Sørensen JL and Polzik ES (2003), "Atomic spins as a storage medium for quantum fluctuations of light", Quantum Info. Comput.. Paramus, NJ, October, 2003. Vol. 3, pp. 518-534. Rinton Press, Incorporated.
Abstract: We review recent results showing the possibility to use off-resonant light/matter interaction for the purpose of quantum memory. A quantum state of atomic spins can be read out by light in a process which is a quantum analogue of the classical Faraday effect. Conversely, the dynamic Stark effect opens up the opportunity for recording the polarization state of light onto the atomic spin memory. We demonstrate that a sample of cesium atoms under appropriate conditions has the sensitivity to record properties of just a few photons, thus being a feasible candidate for quantum memory for light.
BibTeX:
@article{Julsgaard2003, author = {Julsgaard, B. and Schori, C. and Sørensen, J. L. and Polzik,
                    E. S.}, title = {Atomic spins as a storage medium for quantum fluctuations of light}, journal = {Quantum
                    Info. Comput.}, publisher = {Rinton Press, Incorporated}, year = {2003}, month = {October}, volume =
                    {3}, pages = {518--534}, url = {http://portal.acm.org/citation.cfm?id=2011564.2011569} }
Massar S and Polzik ES (2003), "Generating a Superposition of Spin States in an Atomic Ensemble", Physical Review Letters., August, 2003. Vol. 91(6), pp. 060401-+.
Abstract: A method for generating a mesoscopic superposition state of the collective spin variable of a gas of atoms is proposed. The state consists of a superposition of the atomic spins pointing in two slightly different directions. It is obtained by using off resonant light to carry out quantum nondemolition measurements of the spins. The relevant experimental conditions, which require very dense atomic samples, can be realized with presently available techniques. Long-lived atomic superposition states may become useful as an off-line resource for quantum computing with otherwise linear operations.
BibTeX:
@article{Massar2003, author = {Massar, S. and Polzik, E.~S.}, title = {Generating a Superposition of
                    Spin States in an Atomic Ensemble}, journal = {Physical Review Letters}, year = {2003}, month = {August},
                    volume = {91}, number = {6}, pages = {060401-+}, doi = {10.1103/PhysRevLett.91.060401}, eprint = {quant-ph/0306121}
                    }
Polzik ES, Julsgaard B and Sherson J (2003), "Entanglement and quantum teleportation with multi-atom ensembles", Royal Society of London Philosophical Transactions Series A., July, 2003. Vol. 361, pp. 1391-1399.
Abstract: Atomic ensembles containing a large number of atoms have been proved to be an effective medium for quantum-state (quantum information) engineering and processing via their coupling with multi-photon light pulses. The general mechanism of this coupling, which involves continuous quantum variables for light and atoms, is described. The efficient quantum interface between light and atoms has led to the recent demonstration of an entangled state of two macroscopic atomic objects, more precisely two caesium gas samples. Based on this result, a proposal for teleportation of an entangled state of two atomic samples (entanglement swapping) is presented.
BibTeX:
@article{Polzik2003, author = {Polzik, E.~S. and Julsgaard, B. and Sherson, J.}, title = {Entanglement
                    and quantum teleportation with multi-atom ensembles}, journal = {Royal Society of London Philosophical
                    Transactions Series A}, year = {2003}, month = {July}, volume = {361}, pages = {1391--1399}, doi = {10.1098/rsta.2003.1208}
                    }
Sørensen JL, Julsgaard B, Schori C, Hald J and Polzik ES (2003), "Quantum Noise Limited Laser Probing of Atomic Spin States", Laser Physics., March, 2003. Vol. 13(3), pp. 359-367.
BibTeX:
@article{Soerensen2003, author = {J.~L. Sørensen and B. Julsgaard and C. Schori and J. Hald and
                    E.~S. Polzik}, title = {Quantum Noise Limited Laser Probing of Atomic Spin States}, journal = {Laser
                    Physics}, year = {2003}, month = {March}, volume = {13}, number = {3}, pages = {359--367}, url = {http://www.maik.ru/contents/lasphys/lasphys3_3v13cont.htm}
                    }
Sørensen J, Julsgaard B, Schori C and Polzik ES (2003), "Quantum limits encountered in atomic spin measurements", Spectrochimica Acta., June, 2003. Vol. 58, pp. 999-1010.
Abstract: Not Available
BibTeX:
@article{Sorensen2003, author = {Sørensen, J. and Brian Julsgaard and Christian Schori and Eugene
                    S. Polzik}, title = {Quantum limits encountered in atomic spin measurements}, journal = {Spectrochimica
                    Acta}, year = {2003}, month = {June}, volume = {58}, pages = {999--1010}, doi = {10.1016/S0584-8547(03)00060-0}
                    }
Polzik E (2002), "Atomic entanglement on a grand scale", Physics World., September, 2002. Vol. 15(9), pp. 33-37.
Abstract: QUANTUM entanglement is one the weirdest features of quantum mechanics and is at the heart of most of the paradoxes in quantum theory. Erwin Schrödinger considered it to be the most profound characteristics of quantum mechanics and Albert Einstein called it spooky. Entanglement is an attribute that links two or more quantum systems as one and allows particles with two distinct quantum states to have a much closer relationship than classical physics permits. For instance it is possible to create pairs of photons that have their polarizations entangled: if the first photon is circularly polarized in a right-handed sense, then the second photon is always polarized in a left-handed sense, and vice versa.
BibTeX:
@article{Polzik2002, author = {Eugene Polzik}, title = {Atomic entanglement on a grand scale}, journal
                    = {Physics World}, year = {2002}, month = {September}, volume = {15}, number = {9}, pages = {33--37},
                    url = {http://physicsworldarchive.iop.org/index.cfm?action=summary&doc=$152F$92Fphwv15i9a$3040pwa%2Dxml&qt=}
                    }
Schori C, Julsgaard B, Sørensen JL and Polzik ES (2002), "Recording Quantum Properties of Light in a Long-Lived Atomic Spin State: Towards Quantum Memory", Physical Review Letters., July, 2002. Vol. 89(5), pp. 057903-+.
Abstract: We report an experiment on mapping a quantum state of light onto the ground state spin of an ensemble of Cs atoms with the lifetime of 2ms. Recording of one of the two quadrature phase operators of light is demonstrated with vacuum and squeezed states of light. The sensitivity of the mapping procedure at the level of approximately 1 photon/sec per Hz is shown. The results pave the road towards complete (storing both quadrature phase observables) quantum memory for Gaussian states of light. The experiment also sheds new light on fundamental limits of sensitivity of the magneto-optical resonance method.
BibTeX:
@article{Schori2002, author = {Schori, C. and Julsgaard, B. and Sørensen, J.~L. and Polzik, E.~S.},
                    title = {Recording Quantum Properties of Light in a Long-Lived Atomic Spin State: Towards Quantum Memory},
                    journal = {Physical Review Letters}, year = {2002}, month = {July}, volume = {89}, number = {5}, pages
                    = {057903-+}, doi = {10.1103/PhysRevLett.89.057903}, eprint = {quant-ph/0203023} }
Schori C, Sørensen JL and Polzik ES (2002), "Narrow-band frequency tunable light source of continuous quadrature entanglement", Physical Review A., September, 2002. Vol. 66(3), pp. 033802-+.
Abstract: We report the observation of nonclassical quantum correlations of continuous light variables from an altogether different type of source. It is a frequency nondegenerate optical parametric oscillator below threshold, where signal and idler fields are separated by 740 MHz corresponding to two free spectrum ranges of the parametric oscillator cavity. The degree of entanglement observed, -3.8 dB, is the highest to date for a narrow-band tunable source suitable for atomic quantum memory and other applications in atomic physics. Finally we use the latter to visualize the Einstein-Podolsky-Rosen paradox.
BibTeX:
@article{Schori2002a, author = {Schori, C. and Sørensen, J.~L. and Polzik, E.~S.}, title = {Narrow-band
                    frequency tunable light source of continuous quadrature entanglement}, journal = {Physical Review A},
                    year = {2002}, month = {September}, volume = {66}, number = {3}, pages = {033802-+}, doi = {10.1103/PhysRevA.66.033802},
                    eprint = {quant-ph/0205015} }
Hald J and Polzik ES (2001), "Mapping a quantum state of light onto atoms", Journal of Optics B: Quantum and Semiclassical Optics., February, 2001. Vol. 3, pp. 83-+.
Abstract: We derive a theory for mapping a quantum state of nonclassical light onto a collective, excited atomic state via complete absorption of the light. We allow for an arbitrary polarization-squeezed state of light and an arbitrary spin of the atomic ground state. The present derivation thereby generalizes the results of Kuzmich et al. We compare the theory to the recently published experimental results on atomic spin squeezing.
BibTeX:
@article{Hald2001, author = {Hald, J. and Polzik, E.~S.}, title = {Mapping a quantum state of light
                    onto atoms}, journal = {Journal of Optics B: Quantum and Semiclassical Optics}, year = {2001}, month
                    = {February}, volume = {3}, pages = {83-+}, doi = {10.1088/1464-4266/3/1/365} }
Julsgaard B, Kozhekin A and Polzik ES (2001), "Experimental long-lived entanglement of two macroscopic objects", Nature., September, 2001. Vol. 413, pp. 400-403.
Abstract: Entanglement is considered to be one of the most profound features of quantum mechanics1, 2. An entangled state of a system consisting of two subsystems cannot be described as a product of the quantum states of the two subsystems3, 4, 5, 6. In this sense, the entangled system is considered inseparable and non-local. It is generally believed that entanglement is usually manifest in systems consisting of a small number of microscopic particles. Here we demonstrate experimentally the entanglement of two macroscopic objects, each consisting of a caesium gas sample containing about 1012 atoms. Entanglement is generated via interaction of the samples with a pulse of light, which performs a non-local Bell measurement on the collective spins of the samples7. The entangled spin-state can be maintained for 0.5 milliseconds. Besides being of fundamental interest, we expect the robust and long-lived entanglement of material objects demonstrated here to be useful in quantum information processing, including teleportation8, 9, 10 of quantum states of matter and quantum memory.
BibTeX:
@article{Julsgaard2001, author = {Brian Julsgaard and Alexander Kozhekin and Eugene S. Polzik}, title
                    = {Experimental long-lived entanglement of two macroscopic objects}, journal = {Nature}, year = {2001},
                    month = {September}, volume = {413}, pages = {400--403}, doi = {10.1038/35096524} }
Duan L-M, Cirac JI, Zoller P and Polzik ES (2000), "Quantum Communication between Atomic Ensembles Using Coherent Light", Physical Review Letters., December, 2000. Vol. 85, pp. 5643-5646.
Abstract: Protocols for quantum communication between massive particles, such as atoms, are usually based on making use of nonclassical light, and/or superhigh finesse optical cavities are normally needed to enhance interaction between atoms and photons. We demonstrate a remarkable result: by using only coherent light, entanglement can be generated between distant free space atomic ensembles, and an unknown quantum state can thus be teleported from one to another. Neither nonclassical light nor cavities are needed in the scheme, which greatly simplifies its experimental implementation.
BibTeX:
@article{Duan2000, author = {Duan, L.-M. and Cirac, J.~I. and Zoller, P. and Polzik, E.~S.}, title =
                    {Quantum Communication between Atomic Ensembles Using Coherent Light}, journal = {Physical Review Letters},
                    year = {2000}, month = {December}, volume = {85}, pages = {5643--5646}, doi = {10.1103/PhysRevLett.85.5643},
                    eprint = {quant-ph/0003111} }
Hald J, Sørensen JL, Schori C and Polzik ES (2000), "Entanglement transfer from light to atoms", Journal of Modern Optics., September, 2000. Vol. 47(14-15), pp. 2000.
Abstract: We describe an approach to mapping of a quantum polarization state of free propagating light on a collective spin of an atomic ensemble. Recent experimental results on generation of a macroscopic spin squeezed ensemble of cold atoms via interaction with squeezed light are analysed in detail.
BibTeX:
@article{Hald2000, author = {J. Hald and J. L. Sørensen and C. Schori and E. S. Polzik}, title
                    = {Entanglement transfer from light to atoms}, journal = {Journal of Modern Optics}, year = {2000}, month
                    = {September}, volume = {47}, number = {14-15}, pages = {2000}, doi = {10.1080/09500340008232184} }
Kozhekin AE, Mølmer K and Polzik E (2000), "Quantum memory for light", Physical Review A. Vol. 62(3), pp. 033809. American Physical Society.
Abstract: We propose an efficient method for mapping and storage of a quantum state of propagating light in atoms. The quantum state of the light pulse is stored in two sublevels of the ground state of a macroscopic atomic ensemble by activating a synchronized Raman coupling between the light and atoms. We discuss applications of the proposal in quantum information processing and in atomic clocks operating beyond quantum limits of accuracy. The possibility of transferring the atomic state back on light via teleportation is also discussed.
BibTeX:
@article{Kozhekin2000, author = {Kozhekin, A. E. and Mølmer, K. and Polzik, E.}, title = {Quantum
                    memory for light}, journal = {Physical Review A}, publisher = {American Physical Society}, year = {2000},
                    volume = {62}, number = {3}, pages = {033809}, doi = {10.1103/PhysRevA.62.033809} }
Kuzmich A and Polzik ES (2000), "Atomic Quantum State Teleportation and Swapping", Physical Review Letters., December, 2000. Vol. 85, pp. 5639-5642.
Abstract: A set of protocols for atoms-photons and atoms-atoms quantum state teleportation and swapping utilizing Einstein-Podolsky-Rosen light is proposed. The protocols work for polarization quantum states of multiphoton light pulses and macroscopic samples of atoms, i.e., for continuous quantum variables. A simple free space interaction of polarized light with a spin polarized atomic ensemble is shown to suffice for these protocols. Feasibility of experimental realization using gas samples of atoms is analyzed.
BibTeX:
@article{Kuzmich2000a, author = {Kuzmich, A. and Polzik, E.~S.}, title = {Atomic Quantum State Teleportation
                    and Swapping}, journal = {Physical Review Letters}, year = {2000}, month = {December}, volume = {85},
                    pages = {5639--5642}, doi = {10.1103/PhysRevLett.85.5639}, eprint = {quant-ph/0003015} }
Hald J, Sørensen JL, Schori C and Polzik ES (1999), "Spin Squeezed Atoms: A Macroscopic Entangled Ensemble Created by Light", Phys. Rev. Lett.., August, 1999. Vol. 83(7), pp. 1319-1322.
Abstract: We report on the experimental observation of a spin squeezed ensemble of 107 cold atoms. This macroscopic ensemble is generated via quantum state transfer from nonclassical light to atoms.
BibTeX:
@article{Hald1999, author = {Hald, J. and Sørensen, J. L. and Schori, C. and Polzik, E. S.},
                    title = {Spin Squeezed Atoms: A Macroscopic Entangled Ensemble Created by Light}, journal = {Phys. Rev.
                    Lett.}, year = {1999}, month = {August}, volume = {83}, number = {7}, pages = {1319--1322}, doi = {10.1103/PhysRevLett.83.1319}
                    }
Polzik ES (1999), "Einstein-Podolsky-Rosen-correlated atomic ensembles", Physical Review A., June, 1999. Vol. 59, pp. 4202-4205.
Abstract: A method for generating two entangled macroscopic ensembles of atoms via interaction with Einstein-Podolsky-Rosen-correlated light is proposed. The method is directly applicable for creating entanglement between, e.g., two distant atom traps. The proposed special type of partial entanglement is analyzed.
BibTeX:
@article{Polzik1999, author = {Polzik, E.~S.}, title = {Einstein-Podolsky-Rosen-correlated atomic ensembles},
                    journal = {Physical Review A}, year = {1999}, month = {June}, volume = {59}, pages = {4202--4205}, doi
                    = {10.1103/PhysRevA.59.4202} }
Furusawa A, Sørensen JL, Braunstein SL, Fuchs CA, Kimble HJ and Polzik ES (1998), "Unconditional Quantum Teleportation", Science., October, 1998. Vol. 282, pp. 706-+.
Abstract: Not Available
BibTeX:
@article{Furusawa1998, author = {Furusawa, A. and Sørensen, J.~L. and Braunstein, S.~L. and Fuchs,
                    C.~A. and Kimble, H.~J. and Polzik, E.~S.}, title = {Unconditional Quantum Teleportation}, journal =
                    {Science}, year = {1998}, month = {October}, volume = {282}, pages = {706-+}, doi = {10.1126/science.282.5389.706}
                    }
Sørensen JL, Hald J and Polzik ES (1998), "Quantum Noise of an Atomic Spin Polarization Measurement", Physical Review Letters., April, 1998. Vol. 80, pp. 3487-3490.
Abstract: We explore the fundamental noise of the atomic spin measurement performed via polarization analysis of the probe light. The noise is shown to consist of the quantum noise of the probe and the quantum noise of atomic spins. In the experiment with cold atoms in a magneto-optical trap we demonstrate the reduction of the former by 2.5 dB below the standard quantum limit. For the latter we reach the quantum limit set by fluctuations of uncorrelated individual atomic spins. We outline the way to overcome this limit using a recent theoretical proposal on spin squeezing.
BibTeX:
@article{Sorensen1998, author = {Sørensen, J.~L. and Hald, J. and Polzik, E.~S.}, title = {Quantum
                    Noise of an Atomic Spin Polarization Measurement}, journal = {Physical Review Letters}, year = {1998},
                    month = {April}, volume = {80}, pages = {3487--3490}, doi = {10.1103/PhysRevLett.80.3487} }
Kuzmich A, Mølmer K and Polzik ES (1997), "Spin Squeezing in an Ensemble of Atoms Illuminated with Squeezed Light", Physical Review Letters. Vol. 79(24), pp. 4782-4785.
Abstract: We propose an experimentally feasible way to generate spin squeezing in an ensemble of V-type atoms. The proposal involves absorption of a squeezed light beam, and it does not require a large solid angle to be occupied by squeezed light. $50 of the amount of squeezing of the optical field can be transferred onto spin squeezing of the excited atomic states. The analogy with the input-output theory for quantum fields is used to elucidate this result. An experimental setup for generation and detection of spin squeezing within magnetic or hf manifolds is outlined.
BibTeX:
@article{Kuzmich1997, author = {Kuzmich, A. and Mølmer, Klaus and Polzik, E. S.}, title = {Spin
                    Squeezing in an Ensemble of Atoms Illuminated with Squeezed Light}, journal = {Physical Review Letters},
                    year = {1997}, volume = {79}, number = {24}, pages = {4782--4785}, doi = {10.1103/PhysRevLett.79.4782}
                    }