Quantum interference with independent single-photon sources over 300 km fiber

Abstract

.In the quest to realize a scalable quantum network, semiconductor quantum dots (QDs) offer distinct advantages, including high single-photon efficiency and indistinguishability, high repetition rate (tens of gigahertz with Purcell enhancement), interconnectivity with spin qubits, and a scalable on-chip platform. However, in the past two decades, the visibility of quantum interference between independent QDs rarely went beyond the classical limit of 50%, and the distances were limited from a few meters to kilometers. Here, we report quantum interference between two single photons from independent QDs separated by a 302 km optical fiber. The single photons are generated from resonantly driven single QDs deterministically coupled to microcavities. Quantum frequency conversions are used to eliminate the QD inhomogeneity and shift the emission wavelength to the telecommunication band. The observed interference visibility is 0.67 ± 0.02 (0.93 ± 0.04) without (with) temporal filtering. Feasible improvements can further extend the distance to ∼600 km. Our work represents a key step to long-distance solid-state quantum networks.

Quantum Key Distribution using Deterministic Single-Photon Sources over a Field-Installed Fibre Link

“…BB84. More advanced protocols, such as the entanglement based E91 protocol [5,38] or (measurement) device independent QKD protocols [39,40] are not included, as these currently do not compete in terms of key rate, and the structure of the protocol is fundamentally different. When comparing to other experimental achievements we define the concept of a "field trial" as those experiment involving the transmission of the quantum signal over a significant distance exceeding the premises of a single campus area (or the like), on a network infrastructure/channel over which the experimentalists have no control.…”

Epitaxial quantum dots: a semiconductor launchpad for photonic quantum technologies

“…Post-growth frequency tuning techniques are also readily available, which rely on either external strain [46,123,286–289] or electric field [51,59,290–292] , though further efforts are needed to verify whether the frequency tuning techniques are compatible with near-zero FSS [287] . A recent advance has also seen indistinguishable photons to be created between separate quantum dots [57,293,294] [Fig. 7(d)].…”

“…To further mitigate the transmission loss in optical fibers, single photons at telecom wavelengths are desirable. The prevalent approach is to combine the downconversion process in a periodically poled lithium niobate (PPLN) waveguide with the single photons created by quantum dots [294,299–302] . This is a mature technology: an end-to-end conversion efficiency of ∼50% has been achieved [294,302] ; due to a large signal-to-noise ratio, the quality of quantum-dot photons (purity and indistinguishability) can be preserved.…”

“…The prevalent approach is to combine the downconversion process in a periodically poled lithium niobate (PPLN) waveguide with the single photons created by quantum dots [294,299–302] . This is a mature technology: an end-to-end conversion efficiency of ∼50% has been achieved [294,302] ; due to a large signal-to-noise ratio, the quality of quantum-dot photons (purity and indistinguishability) can be preserved. PPLN waveguides are, however, centimeters long, and not compatible with nanophotonic fabrication processes.…”

Hong-Ou-Mandel interference from distinct molecules on the same chip

“…While MDI-QKD has been implemented using attenuated laser pulses 15 and parametric single-photon sources, 16 only preliminary demonstrations have been explored with deterministic single-photon emitters. 17 In this context, organic molecules are promising candidates as efficient emitters of pure single-photons which are also mutually indistinguishable, as assessed in Fig. 1).…”