This letter clarifies properties of system using squeezed state signal in photon channel with energy loss. It is found that error rate of squeezed state system is always superior to that of coherent state, and that reduction of optimum squeezing parameter is allowed by optimization taking into account loss in comparison with optimization of transmitter squeezed state.

Optical communication systems using quantum state control have received much attentions. For this quantum state control communication, however, one of the most serious problems is the effect of transmission loss which degrades the advantage of the quantum state controlled signal. In optical long transmission communications, in general, transmission loss is large so that the advantage using quantum state controlled signal is hardly lost and performance of quantum state control communications is almost equal to that of conventional communications. So it is necessaty for a new application of quantum state control to overcome the standard quantum limitation which is achieved by the conventional coherent communication system. In this paper, we propose a realization of a new optical communication system with received quantum state controller, so called Received Quantum State Control (RQSC) system, in order to cope with transmission loss problem. This system can provide the advantage of quantum state control regardless of amount of transmission loss. Particularly, it is shown that the system can overcome the standard quantum limitation which corresponds to the limitation achieved by conventional BPSK homodyne system using coherent state signal. This corresponds to Quantum Receiver" of the broad sense in Helstrom's receiver theory.

In this paper, we analyze photon distributions of squeezed state from a viewpoint of quantum state control communications (QSCC). Especially, the effect of the channel loss on these properties are shown in transmitted quantum state control (TQSC). As a result, we show the general property of the photon distribution of squeezed state suffering the loss effect in channel with respect to the transparence efficiency. Although the photon distribution of squeezed state suffering the loss effect approaches the Poissonian one, the photon distribution on the way becomes a remarkable one in some region of a squeezing parameter. Then we show optimum conditions of squeezed state based on Signal to noise ratio (SNR) in the photon counting system. It is found that the degree of the squeezing to minimize error probability is much smaller than that for SNR. Moreover, we compare properties of the photon counting system using a squeezer as a preamplifier with those using a general linear optical amplifier.