  Quantum key distribution allows secret key generation with information
theoretical security. It can be realized with photonic integrated circuits to
benefit the tiny footprints and the large-scale manufacturing capacity.
Continuous-variable quantum key distribution is suitable for chip-based
integration due to its compatibility with mature optical communication devices.
However, the quantum signal power control compatible with the mature photonic
integration process faces difficulties on stability, which limits the system
performance and causes the overestimation of secret key rate that opens
practical security loopholes. Here, a highly stable chip-based quantum signal
power control scheme based on a biased Mach-Zehnder interferometer structure is
proposed, theoretically analyzed and experimentally implemented with standard
silicon photonic techniques. Simulations and experimental results show that the
proposed scheme significantly improves the system stability, where the standard
deviation of the secret key rate is suppressed by an order of magnitude
compared with the system using traditional designs, showing a promising and
practicable way to realize highly stable continuous-variable quantum key
distribution system on chip.
