QUANTUM DETECTION FOR ON-OFF KEYED MIXED-STATE SIGNALS WITH A SMALL AMOUNT OF THERMAL NOISE

The detection strategy proposed previously by the authors for binary p ure-state signals, which consists of a unitary transformation and phot on counting afterward [Phys. Rev. A 54, 2728 (1996)], can also be appl ied to the case of on-off keyed signals of coherent states with a smal l amount of thermal noise. It yields an error level almost the same as the quantum minimum bound in practical parameter region.