Towards heterogeneous quantum networks with solid state single photon sources and atomic quantum memories

Quantum networks promise radically new applications and novel insights [1]: High-speed quantum cryptography networks will be used for unconditionally secure communication in metropolitan areas, and memory enhanced quantum... [ view full abstract ]

Quantum networks promise radically new applications and novel insights [1]: High-speed quantum cryptography networks will be used for unconditionally secure communication in metropolitan areas, and memory enhanced quantum computers and simulators will allow for exponential speed-up in solving complex problems [2]. However, establishing the hardware for a quantum network is challenging.  Sources of indistinguishable single photons are required, along with a means to store the single photons [3]. We report on our efforts to build the basic element of quantum networks: A semiconductor quantum dot (QD) single photon source [4,5] coupled to a compatible atomic quantum memory [6].

On the one hand we developed a rubidium quantum memory for broadband operation, matched to the QD exciton natural decay rate. The memory is demonstrated using attenuated laser pulses on the single photon level with a bandwidth of 0.66 GHz.  In the present memory, the readout noise is dominated by atomic fluorescence, and for input pulses containing on average μ1 = 0.27(4) photons the signal to noise level would be unity. On the other hand, we demonstrate deterministic single photon shaping with QDs, to match the narrow transitions of Rubidium [5].

[1] H.J. Kimble, “The quantum internet,” Nature 453, 1023 (2008).

[2] T. D. Ladd et al., “Quantum computers,” Nature 464, 45 (2010).

[3] N. Sangouard et al., “Quantum repeaters based on atomic ensembles and linear optics,” Rev. Mod. Phys. 83, 33 (2011).

[4] J.-P. Jahn et al., “An artificial Rb atom in a semiconductor with lifetime-limited linewidth,” Phys. Rev. B 92, 245439 (2015).

[5] L. Beguin et al., “On-demand semiconductor source of 780 nm single photons with controlled temporal wave packets,” arXiv:1710.02490 (2017).

[6] J. Wolters et al., “Simple atomic quantum memory suitable for semiconductor quantum dot single photons,” Phys. Rev. Lett. 119 060502 (2017).

Figure: (a) Energy levels of the Rb D1 line and transitions involved in the memory experiments.  (b) Arrival time histogram for the photons detected in a memory experiment with a storage time 50 ns, for a coherent input state containing one photon. Signal to noise ratio SNR = 3.7(6) for the single photon level input pulse.