Some quantum problems in optical communications

John S. Baras

C. Bendjaballah, Osamu Hirota, Serge Reynaud

Robert S. Kennedy

Various approaches to the problem of controlling quantum noise, the dominant noise in an optical communications system, are discussed. It is shown that, no matter which way the problem is approached, there always remain uncertainties. These uncertainties exist because, to date, only very few communication problems have been solved in their full quantum form.

Ivan B. Djordjević

This paper addresses two important problems of interest for deep-space optical communications, quantum inter-chip/intra-chip optical communications and quantum-key distribution: 1) the problem of codedM-ary phase-shift keying optical coherent-state quantum communication in the absence of background radiation, and 2) the problem of coded binary coherent state communication in the presence of background radiation. In both cases large girth low-density parity-check (LDPC) codes are used as channel codes. With girth-10 LDPC-code of rate 0.8 and BPSK, the bit-error ratio of 10-8can be achieved for average number of signal photons of 0.73, resulting in net-effective coding gain of 7.63 dB.

Konrad Banaszek

Raúl García−Patrón, Carlos Navarrete–Benlloch, Seth Lloyd +2 more

Optical parametric amplifiers together with phase-shifters and beamsplitters have certainly been the most studied objects in the field of quantum optics. Despite such an intensive study, optical parametric amplifiers still keep secrets from us. We will show how they hold the answer to one of the oldest problems in quantum communication theory, namely the calculation of the optimal communication rate of optical channels.