Algorithms and devices for metropolitan-scale quantum key distribution

Abstract

Secure communication against any possible eavesdropper is important in today's Internet. Quantum key distribution (QKD), along with the one-time pad cryptosystem, provides a quantum-secure way for two distant parties to communicate with composable security. It has recently become clear that a wide-spread utilization of QKD warrants improvements in its implementations. Theoretically, the security of QKD is difficult to analyze and the effects of imperfections on key rates is difficult to estimate. Practically, QKD requires miniaturization and an operation speed comparable to current Internet communications. In this thesis, we develop a robust numerical approach for calculating the key rates for arbitrary QKD protocols with explicitly quantifiable security. The approach formulates semidefinite programs that take, as inputs, the observed statistics from a QKD session and outputs the guaranteed key rates. Next, in an effort to boost the operation speed of current QKD systems, we describe a large-alphabet QKD scheme that can transmit multiple secret bits of information per photon while being immune against a photon-number side channel attack. We also demonstrate the feasibility of this system with an intercity field demonstration that pushes the boundary on its key generation rate. We then present the miniaturization of QKD systems using the silicon photonics platform which allows for the integration of multiple high-speed photonic operations into a single circuit. We present the first intercity field demonstrations of QKD that demonstrates silicon photonics-supported by the currently existing CMOS technology-can pave the way for a high-speed metropolitan-scale quantum communication network.