  Integrated photonics offers great potential for quantum communication devices
in terms of complexity, robustness and scalability. Silicon photonics in
particular is a leading platform for quantum photonic technologies, with
further benefits of miniaturisation, cost-effective device manufacture and
compatibility with CMOS microelectronics. However, effective techniques for
high-speed modulation of quantum states in standard silicon photonic platforms
have been limited. Here we overcome this limitation and demonstrate high-speed
low-error quantum key distribution modulation with silicon photonic devices
combining slow thermo-optic DC biases and fast (10~GHz bandwidth)
carrier-depletion modulation. The ability to scale up these integrated circuits
and incorporate microelectronics opens the way to new and advanced integrated
quantum communication technologies and larger adoption of quantum-secured
communications.
