Retrodiction for quantum optical communications
Stephen Mark Barnett, David Thomas Pegg, John R. Jeffers, Ottavia Jedrkiewicz, R. Loudon · Physical Review A · 2000
Given the result of a measurement on the output of a quantum optical communication channel, we show how to calculate a retrodictive state at the input. This state can be used by the receiver to determine the probability that any one of a given set of states was selected by the transmitter. We establish the remarkably simple result that retrodicting the prepared input signal for an attenuating (amplifying) channel corresponds to predicting the measured output signal for an amplifying (attenuating) channel.