Single-Photon Interference in Sidebands of Phase-Modulated Light for Quantum Cryptography

Abstract

We report single-photon interference in the sidebands of modulated light. The relative phase of interacting quantum states is reliably controlled by the phase of a low-frequency modulating signal. We show how this type of interference can be used to build a robust system for quantum cryptography. An experiment was implemented at 1540 nm, over a 20-km-long standard single-mode fiber, using a germanium singlephoton avalanche photodiode.