摘要：

Quantum information protocols require light sources emitting single indistinguishable photons. In this context, the semiconductor quantum dots, which are considered as two-level systems in the artificial atom model, are good candidates for the development of such sources in the solid state with the great advantage that they could be integrated into on-chip devices. However, their interaction with the solid state environment reduces the photon coherence time and thus broadens their emission spectrum which makes the emitted photons partially distinguishable over time. A characteristic time of the photon indistinguishability is thus tightly linked to the photon coherence time of these emitters which is typically of the order of few hundreds of picoseconds and which makes difficult the use of conventional photodetectors with nanosecond time resolutions.

In this talk, I will first show that improving the coherence of the photons until the one imposed by the radiative limit (i.e. T2 = 2T1, T1 and T2 being the lifetime and the coherence time, respectively) can be achieved by performing strictly resonant excitation of a quantum dot at low temperature. Nevertheless, a fine control of the electrostatic environment related to the nanostructures residual doping remains a major challenge to answer the widely encountered problem of the inhibition of the resonance fluorescence of a quantum dot. Meanwhile, we demonstrated that the resonant Rayleigh scattering regime, where the coherently scattered single photons inherit the coherence time of the excitation laser, paves the way to the development of "ultra-coherent" sources of single photons with high degrees of indistinguishability. In this regime where the laser tailors the coherence of the photons and where the radiative limit becomes a secondary requirement, two photons emitted successively by the same quantum dot are indistinguishable on time scales never measured before for a solid nano-emitter. In fact, photon temporal indistinguishability of more than a dozens of nanoseconds can be reached and controlled by simply varying the spectral width of the excitation laser.
 
References

[1] H. S. Nguyen, G. Sallen, C. Voisin, Ph. Roussignol, C. Diederichs, and G. Cassabois, “Optically Gated Resonant Emission of Single Quantum Dots”, Phys. Rev. Lett. 108, 057401 (2012).
[2] H. S. Nguyen, G. Sallen, M. Abbarchi, R. Ferreira, C. Voisin, Ph. Roussignol, G. Cassabois, and C. Diederichs, “Photoneutralization and slow capture of carriers in quantum dots probed by resonant excitation spectroscopy”, Phys. Rev. B 87, 115305 (2013).
[3] H. S. Nguyen, G. Sallen, C. Voisin, Ph. Roussignol, C. Diederichs, and G. Cassabois, “Ultra-coherent single photon source”, Appl. Phys. Lett. 99, 261904 (2011).
[4] R. Proux, M. Maragkou, E. Baudin, C. Voisin, Ph. Roussignol, and C. Diederichs, “Measuring the photon coalescence time window in the continuous-wave regime for resonantly driven semiconductor quantum dots”, Phys. Rev. Lett. 114, 067401 (2015).
 
报告人简历：

Carole Diederichs is an Associate Professor at University Pierre & Marie Curie (UPMC, France). She graduated from UPMC with a PhD in Quantum Physics in 2007. She did her PhD studies in the "Coherent and Non-Linear Optics" group at Laboratoire Pierre Aigrain (LPA, France), under the supervision of Jér?me Tignon, on the optical parametric oscillation in semiconductor microcavities for the generation of twin photons. In 2007, she received the Michelin Young Researcher Award from the French Society of Physics (SFP). After her post-doctoral research at the Research Laboratory of Electronics (RLE) at Massachusetts Institute of Technology (MIT, USA), she joined UPMC as an Associate Professor in 2008, to work on the optical spectroscopy of single semiconductor InAs/GaAs quantum dots in LPA. Her research activity focused on quantum optics experiments for the realization of indistinguishable single photon sources. She is currently a Visiting Associate Professor at Nanyang Technological University (NTU, Singapore) in the group of Prof. Qihua Xiong (NTU-SPMS-PAP), and also a member of MajuLab (CNRS-UNS-NUS-NTU International Joint Research Unit, Singapore).
 

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