Experimental demonstration of a quantum receiver beating the standard quantum limit at the telecom wavelength

Abstract

Discrimination of coherent states beyond the standard quantum limit (SQL) is an important task not only for quantum information processing but also for optical coherent communication. In order to optimize long distance optical fiber networks, it is of practical importance to develop a quantum receiver beating the SQL and approaching the quantum bound at telecom wavelength. In this paper, we experimentally demonstrate a receiver beating the conventional SQL at telecom wavelength. Our receiver is composed of a displacement operation, a single photon counter and a real time adaptive feedback operation. By using a high performance single photon detector operating at the telecom wavelength, we achieve a discrimination error beyond the SQL. The demonstration in the telecom band provides the first step important towards quantum and classical communication beyond the SQL using a coherent state alphabet, and we envision that the technology can be used for longdistance quantum key distribution, effective quantum state preparation and quantum estimation.