Fundamental limits to the secure key rate of quantum key distribution using Gaussian-modulated coherent states in the presence of quantum noise and device mismatch uncertainty

High-speed quantum key distribution enables unconditionally secure communication, but has not been in widespread usage yet in part due to its slow secure data rate. By exploiting photonic integrated circuit technologies for near infrared wavelengths, continuous-variable quantum key distribution using Gaussian-modulated coherent states has been recently reported to operate at room temperature in a chip-scale realization. Nevertheless, the highest secure key rate achieved is still well below the multi-gigabit capability of conventional optical communication technologies. Measured noise characteristics of silicon transistors show that the fundamental limits to the secure key rate may come from the device mismatch uncertainty, which is inherent in the physical realization of a balanced optical quantum key distribution receiver for the detection of Gaussian-modulated coherent states. Here we discuss simulation results on a programmable silicon quantum photonic integrated circuit, predicting that the programmability can mitigate the impact of device mismatch and thus a multi-gigabit/sec secure key rate will be achieved in line-of-sight free-space optical quantum channels and short-distance fiber channels.