Multiuser detection in a quantum channel

The use of multiuser detection techniques in multiple access optical channels has been studied in the literature, with emphasis on optical CDMA. In general, it has been assumed that the optical detection is carried out by p-i-n diodes, which count the photons present in the field. However, the theory of quantum detection indicates that other measurements might yield significantly smaller error probabilities. In this paper, we show by example that this can happen in the multiple-access case. We also note that the quantum multiuser detection problem differs from the classical one, in that quantum measurement precludes the use of matched filter banks for non-orthogonal signals.