Toward quantum-dot based optical quantum networks

Semiconductor quantum dots (QDs) are very promising artificial atoms for quantum information  processing; they can generate flying quantum bits in the form of single photons or polarization  entangled photon pairs. They show single photon sensitivity, which can be used to implement quantum  logic gates; and, last but not least, the spin of a carrier trapped in a QD can be used as a quantum  memory. The scalability of a QD based quantum network requires having efficient interfaces between  stationary and flying quantum bits, i.e. between the QD and a single photon. In the last few years, our  group has made significant progresses in this direction using cavity quantum electrodynamics.  We have developped a near-optimal QD-photon interface by  deterministically positioning a single QD in a microcavity: we can  control the QD spontaneous emission at will [1].

By adding an  electrical control to the device [2], the charge noise is minimized  and the QD state is shown to be mostly free from decoherence at  10K. In the latest generation devices, the incident photons interact  with the QD with probability 0.95, which radiates back in the cavity  mode with probability >0.93. In such devices, the state of the QD-  based artificial atom can be coherently manipulated with a pi-pulse  obtained for only 3.8 incident photons [3]. 

Based on such structures, bright solid-state single-photon sources  are reproducibly fabricated: the single photon purity is above 98%  and the indistinguishability of successively emitted photons can be  as large as 99.5%. The brightness of the source exceeds by a factor 20 the one of today’s most used  sources for optical quantum technologies [4]. We also develop devices performing as a nonlinear  switch at the single-photon level that can convert a coherent pulse into a highly non-classical light  wavepackets [5]. 

References 

[1] A. Dousse et al. , Phys. Rev. Lett. 101, 267404 (2008),  A. Dousse, et al. , Appl. Phys. Lett. 94, 121102 (2009) 

[2] A. Nowak et al., Nature Communications 5, 3240 (2014) 

[3] V. Giesz et al., Nature Communications 7, 11986 (2016) 

[4] N. Somaschi, et al. Nature Photonics 10, 340 (2016). 

[5] L. De Santis et al, arXiv:1607.05977