Atomically-thin single-photon sources for quantum communication

Abstract

To date, quantum communication widely relies on attenuated lasers for secret key generation. In future quantum networks, fundamental limitations resulting from their probabilistic photon distribution must be overcome by using deterministic quantum light sources. Confined excitons in monolayers of transition metal dichalcogenides (TMDCs) constitute an emerging type of emitter for quantum light generation. These atomically thin solid-state sources show appealing prospects for large-scale and low-cost device integration, meeting the demands of quantum information technologies. Here, we pioneer the practical suitability of TMDC devices in quantum communication. We employ a WSe2 monolayer single-photon source to emulate the BB84 protocol in a quantum key distribution (QKD) setup and achieve click rates of up to 66.95 kHz and antibunching values down to 0.034—a performance competitive with QKD experiments using semiconductor quantum dots or color centers in diamond. Our work opens the route towards wider applications of quantum information technologies using TMDC single-photon sources.

Monolayer-Based Single-Photon Source in a Liquid-Helium-Free Open Cavity Featuring 65% Brightness and Quantum Coherence

“…It is worth noting that this value approaches the current state of the art in solid-state single-photon sources based on III/V QDs 42−44 and widely outperforms monolayer-based triggered single-photon sources reported in any implementation. 15,39,45,46 It furthermore is interesting to note that the congruence of directly measured first-lens brightness and theoretically calculated source extraction efficiency suggests that the internal quantum efficiency of our emitters approaches unity. We believe that this encouraging result was facilitated by the combination of utilizing high-quality TMDC materials and capping via hexagonal boron nitride, the resonant coupling to the photonic cavity, and finally the applied quasi-resonant pumping scheme, which does not allow for losses via highmomentum free-exciton states or relaxation into long-lived dark exciton states.…”

“…It is interesting to note that this wavelength, which is widely tunable via piezo strain, is very close to the technologically relevant Rb-87-D2 line, with the potential for a quantum memory in future repeater networks . Moreover, the emission wavelength is also compatible with free-space quantum communication applications . The spectral line width of the QD is limited by the resolution of our detection system of 200 μeV (see Figure S5 of the Supporting Information for a high-resolution spectrum).…”

Polarization dynamics of solid-state quantum emitters

“…We speculate that this effect could be due to the local electric field induced by the excess charges that are excited with the laser pulse, which is also supported by DFT calculations. We believe that the observed temporal change of polarization in various solid-state quantum emitter systems is critical to reach the ideal performance of these emitters for several applications, such as to generate the Fouriertransform limited photons [41,42] or to achieve lower quantum bit error rate in quantum key distribution systems [27,43]. It might even be an important step toward achieving indistinguishable single photons from a room temperature solid-state quantum light source when coupled with resonant structures [44].…”

Deterministic Localization of Strain-Induced Single-Photon Emitters in Multilayer GaSe

“…Note that the incident laser power density is critical in the single-photon purity. Previous studies of SPEs in quantum dots, carbon nanotubes, color centers in diamond, and WSe 2 have demonstrated that a low excitation power density is required to minimize the emergence of additional excited states that can reduce the SPE purity. Power-dependent photon antibunching has been extensively investigated in WSe 2 , and hBN , SPEs, but remains underexploited in GaSe SPEs.…”