Sources of highly indistinguishable single photons with semiconductor quantum dots under resonant excitation"

International audiencePhotons have been under extensive investigation regarding their possible role as ideal flying qu-bits in a quantum network. Numerous applications for single photon sources have already been proposed but most of them require consecutive photons to have identical wave packets, i.e. to be indistinguishable. Resonance fluorescence of the excitonic transition in epitaxial quantum dots (QDs) has also caught the attention of the community1 as it can generate high quality, dephasing-free photons which inherit the laser properties in terms of coherence in the resonant Rayleigh scattering regime2 Our sample consists of self-assembled InAs/GaAs QDs embedded in a planar GaAs microcavity formed by two distributed-Bragg reflectors. Resonant excitation of single QDs is achieved by a cw tuneable diode laser with a variable coherence length in an orthogonal excitation-detection setup. A Hanbury Brown and Twiss (HBT) setup is used in order to deduce the second-order correlation function g(2)(τ). One-photon interference. In this work, we demonstrate the generation of highly indistinguishable photons from a single QD, by performing one and two photon quantum interference measurements. 3 is investigated via monitoring the light field intensity at the output of a beam splitter of a Michelson interferometer while with a Hong-Ou-Mandel interferometer two-photon interference4 HBT measurements for various input powers show that our QD operates as an ideal single photon emitter in both regimes of resonant Rayleigh scattering and resonance fluorescence. One-photon interference experiments demonstrate that when decreasing the excitation power, we enter in a regime where, due to resonant Rayleigh scattering, the emitted photons inherit the same coherence of the excitation source. We therefore study the evolution of the degree of indistinguishability of these photons, concentrating in this scarcely studied but very promising low power regime, where the single photon emission is combined with long coherence times, making possible the observation of high levels of indistinguishability. measurements are performed. Our experimental results suggest that the QDs provide an ideal system that should be further exploited in the specific resonant Rayleigh scattering regime for the development of quantum networks, on the basis of linear optics quantum computation, entanglement etc. 1 Muller, A. et al., Phys. Rev. Lett. 99, 187402 (2007) ; Melet, R. et al., Phys. Rev. B 78, 073301 (2008) ; Ates, S. et al., Phys. Rev. Lett. 103, 167402 (2009) ; Vamivakas, A. N. et al., Nat. Phys. 5, 198 (2009) ; Nguyen, H. S., et al., Phys. Rev. Lett. 108, 057401 (2012) ; Reinhard, A. et al., Nat. Phot. 6, 93 (2012). 2 Nguyen, H. S. et al., Appl. Phys. Lett. 99, 261904 (2011). 3 L. Mandel. Reviews of Modern Physics, 71, 274 (1999). 4 Hong, C. K., Ou, Z. Y. & Mandel, L. Rev. Lett. 59, 2044 (1987)