Secure quantum communication with pseudo-single photon states

Abstract

We introduce an optical quantum state that can fundamentally mimic a single photon state not only with respect to the number of photons but also in terms of an indeterminate phase. Such a state, defined as a state in the superposition of weak coherent states equally distributed on a circle in phase space, is close to a perfect single photon state with almost unit fidelity. Moreover, it exhibits fundamental features of single photons such as Hong-Ou-Mandel interference. Remarkably, by applying it for the implementation of quantum key distribution (QKD), we show that it allows us to achieve higher key generation rates over longer distances than the typical approach using weak coherent states. We expect that our work paves an alternative way to the realization of efficient secure quantum communication as well as photonic quantum information processing.