Quantum Optics Seminar by Xiao-Liu Chu
A single molecule as a high-fidelity photon gun for
producing intensity-squeezed light
Xiao-Liu Chu1,2, Stephan Götzinger2,1,3, and Vahid Sandoghdar1,2,3
1. Max Planck Institute for the Science of Light, 91058 Erlangen, Germany
2. Department of Physics, Friedrich Alexander University, 91058 Erlangen, Germany
3. Graduate School in Advanced Optical Technologies (SAOT), 91058 Erlangen, Germany
One efficient approach for generating single photons is based on using a two-level atom, which inherently cannot emit more than one photon at the time. As early as the 1980s, this quantum feature was identified as the gateway to creating single photon sources (SPS’s), where a regular excitation sequence would produce a stream of photons with photon number fluctuations below the shot noise. Such an ideal intensity squeezed SPS would be desirable for a range of applications, including quantum imaging, sensing, enhanced precision measurements and information processing.
Experimental realizations of such deterministic SPS's have been hindered by large losses caused by low photon collection efficiencies and photophysical shortcomings. By using a planar metallo-dielectric antenna applied to an organic molecule, we have now demonstrated the most regular stream of single photons reported to date . We use planar metallo-dielectric antennas for re-shaping the emission of a single emitter into a solid angle that is small enough to be collected by a conventional objective lens. The basic antenna design concept is very simple: a layered dielectric structure made of different polymers is coated on a conventional cover glass, where the key feature is the stepwise decrease in refractive index. A metallic mirror on the top side increases the collection efficiency to above 99% compared to our first dielectric design .
We determine the sub-Poissonian nature of our SPS from the detected count rate and its fluctuations. The intensity noise is reduced by 40% compared to the fluctuations of a shot-noise limited source of the same intensity. The best result of our measurements reaches an intensity squeezing of 2.2 dB, which is limited by our detector.
The sub-shot-noise stream of single photons demonstrated in this work can be used to calibrate photodetectors and counters at ultra-low light levels and allow detection, spectroscopy, and imaging of samples with weak optical response, such as nanoparticles or biochemical traces. Furthermore, other applications such as quantum key distribution will benefit from a very high efficiency in creating photons on demand.
 X.-L. Chu, S. Götzinger, V. Sandoghdar, “A single molecule as a high-fidelity photon gun for producing intensity-squeezed light,” Nature Photonics 11, 58 (2017).
 K.-G. Lee, X.-W. Chen, H. Eghlidi, P. Kukura, R. Lettow, A. Renn, V. Sandoghdar, S. Götzinger, “A planar dielectric antenna for directional single-photon emission and near-unity collection efficiency” Nature Photonics 5, 166 (2011).