PhD defense by Petru Tighineanu – University of Copenhagen

QUANTOP > Quantum Optics Calendar > Calendar 2015 > PhD defense by Petru T...

PhD defense by Petru Tighineanu

Title: Electric and magnetic interaction between quantum dots and light. 

At the intersection between quantum optics and solid-state physics, the field of quantum photonics has unfolded over the past years striving to combine the expertise developed for atoms and the scalability demonstrated by solid-state systems. To this end, quantum dots provide the essential link between light and matter degrees of freedom. The ability to tailor the density of vacuum fluctuations around quantum dots has resulted in tremendous progress in manipulating single quantum-dot excitations over the past decade [1]. 

Conventional quantum emitters interact only with the electric-field component of light and are completely blind to the magnetic field. The recent experimental demonstration that the dipole theory may break in In(Ga)As quantum dots [2] motivated us to develop a theory of spontaneous emission from quantum dots. We find that quantum dots are a novel class of emitters that are sensitive to the magnetic field of light [3]. We pinpoint the microscopic mechanism governing the magnetic sensitivity and show that the underlying lattice distortion generates curved quantum-mechanical currents flowing over mesoscopic length scales inside the quantum dot [4]. Both fundamental science and quantum technologies may greatly benefit from these findings. For instance, novel photonic environments could be designed to match the curved current-density pattern of the quantum dot. This opens the prospect for the realization of a quantum-dot based quantum metamaterial combining the fascinating phenomena inherent to classical metamaterials with single-photon nonlinearities and non-classical statistics of light pertaining to the quantum world.
Quantum dots greatly benefit from their multi-body nature with enhanced light-matter interaction strength. Commonly employed quantum dots have, however, an upper limit for the interaction strength with light, regardless of their size and shape. In the present work we demonstrate that monolayer-fluctuation quantum dots can be used to enhance the interaction strength with light far beyond that of conventional quantum dots [5]. This is caused by the superradiant nature of excitons, which may be of great interest for fundamental science and technology alike. In particular, such rapid radiative decays will likely exceed all dephasing mechanisms resulting in highly coherent flying quantum bits, of high relevance for their use in quantum-information science. New and so far largely unexplored solid-state quantum-electrodynamics regimes involving energy non-conserving virtual processes, such as the ultra-strong coupling between light and matter, may become within reach at optical frequencies for the first time. 

Selected publications: 

[1] P. Lodahl, S. Mahmoodian and S. Stobbe, Interfacing single photons and single quantum dots with photonic nanostructures,

[2] M. L. Andersen, S. Stobbe, A. S. Sørensen, and P. Lodahl, Strongly modified plasmon-matter interaction with mesoscopic quantum emitters, Nat. Phys. 7, 215 (2011)

[3] P. Tighineanu, M. L. Andersen, A. S. Sørensen, S. Stobbe, P. Lodahl, Probing electric and magnetic vacuum fluctuations with quantum dots, Phys. Rev. Lett. 113, 043601 (2014)

[4] P. Tighineanu, A. S. Sørensen, S. Stobbe, P. Lodahl, Unraveling the mesoscopic character of quantum dots in nanophotonics,
[5] P. Tighineanu, R. S. Daveau, T. B. Lehmann, H. E. Beere, D. A. Ritchie, P. Lodahl, and S. Stobbe, Single-photon Dicke superradiance from a quantum dot, to be submitted 

Assessment Committee: 

Professor David Gershoni, The Technion – Israel Institute of Technology, Israel

Professor Andreas Knorr, Technical University of Berlin, Germany

Professor Karsten Flensberg, The Niels Bohr Institute, Denmark