  Quantum key distribution (QKD) is a well-known application of quantum
information theory that guarantees information-theoretically secure key
exchange. As QKD becomes more and more commercially viable, challenges such as
scalability, network integration, and high production costs need to be
addressed. Photonic and electronic integrated circuits that can be produced in
large volumes at low cost hold the key to large-scale deployment of
next-generation QKD systems. Here, we present a continuous-variable (CV) QKD
system using an integrated photonic-electronic receiver that combines a silicon
photonic integrated circuit implementing a phase-diverse receiver with
custom-designed GaAs pHEMT transimpedance amplifiers. The QKD system operates
at a classical telecom symbol rate of 10 GBaud, generating high secret key
rates exceeding 0.7 Gb/s over a distance of 5 km and 0.3 Gb/s over a distance
of 10 km. The secret keys are secure against collective attacks with
finite-size effects taken into account. Well-designed digital signal processing
enabled the high-speed operation. Our experiment sets a new record for secure
quantum communication and paves the way for the next generation of CV-QKD
systems.
