Runjia Zhang

In recent years, continuous-variable (CV) quantum communication has become a nascent but promising alternative to secure multiple end-users sharing the same telecommunication backbone. Continuous-variable quantum key distribution (CV-QKD) with reverse reconciliation enables natural scalability from point-to-point communication to quantum access networks with passive quantum broadcasting channels. Here, we report two experimental demonstrations on a $1:4$ quantum communication network with protocols advancing from two fronts, either moving beyond the asymptotic limit or the Gaussian assumption of the modulation. We demonstrate for the first time a network of four active users simultaneously achieving high secret key rates with finite-size security against collective attacks. A comprehensive security analysis was performed to cover different scenarios on how each end user prefers to trust others. In addition, with the same optical configuration, we implement an initial CV quantum network accounting for four users (two active) with discrete modulation with the conservative untrusted broadcast protocol. The results establish the viability of CV quantum network for practical security with imperfect devices when broadly deployed to connect end users to existing infrastructures.

Measurements in quantum physics are inherently random. Moreover, it is possible to certify quantum randomness from systems that are only partially characterized by the user. Here, we propose a simple quantum random number generator (QRNG) that requires only a single photodiode and one laser. We trust only the quantum efficiency of the photodiode and the characterization of the detector, leaving the laser in control of the eavesdropper. Such a QRNG is source-device-independent and its optical setup is among the simplest setups achieving source-device independence.