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.

Single-photon light detection and ranging (lidar) offers single-photon sensitivity and picosecond timing resolution, which is desirable for high-precision three-dimensional (3D) imaging over long distances. Despite important progress, further extending the imaging range presents enormous challenges because only a few echo photons return and are mixed with strong noise. Here, we tackled these challenges by constructing a high-efficiency, low-noise coaxial single-photon lidar system and developing a long-range-tailored computational algorithm that provides high photon efficiency and good noise tolerance. Using this technique, we experimentally demonstrated active single-photon 3D imaging at a distance of up to 45 km in an urban environment, with a low return-signal level of ～1 photon per pixel. Our system is feasible for imaging at a few hundreds of kilometers by refining the setup, and thus represents a step towards low-power and high-resolution lidar over extra-long ranges.

We report a quantum key distribution (QKD) system that uses light-emitting-diodes (LEDs) at 1310 nm as optical sources. Compared to the normally used laser diodes (LDs), LEDs are easier to manufacture and integrate, and thus have the potential to reduce the costs of practical systems. To demonstrate the feasibility of a low-cost, integratable QKD system that aims at meeting the demand of the last-mile secure communication, we utilize LEDs at 1310 nm as the optical sources, while using only passive optical components and only one single photon detector at the receiver’s side. With a repetition rate of 10 MHz, we obtain secure key rates of 10.9 kbps within the experimental time of 1000 s over a fiber length of 1 km.