Quantum interference between independent solid-state single-photon sources separated by 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 GHz 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 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\pm0.02 (0.93\pm0.04) 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.

High-Performance Single-Photon Sources at Telecom Wavelength Based on Broadband Hybrid Circular Bragg Gratings

“…Hybrid circular Bragg gratings (CBGs) have recently emerged as a promising alternative to those platforms thanks to the presence of a backside gold mirror, which eliminates the loss of photons into the substrate as well as the issue of a fragile free-standing membrane that affects the original suspended version. − The first experiments with hybrid CBGs showed the ability to provide a moderate Purcell enhancement of both the exciton and the biexciton transitions as well as high extraction efficiency in a wide range of wavelengths, , leading to count rates >10 MHz. , However, they focused on the spectral region between 780 and 880 nm, which prevents their integration with the standard optical fiber infrastructure due to strong attenuation (>1 dB/km) at those wavelengths. Despite the publication of various design studies − and the demonstration of a device operating in the O-band, similar results at telecom wavelength have not been achieved yet and the degree of reproducibility remains an open question.…”