  We present a quantum receiver for quadrature amplitude modulation (QAM)
coherent states discrimination with homodyne-displacement hybrid structure. Our
strategy is to carry out two successive measurements on parts of the quantum
states. The homodyne result of the first measurement reveals partial
information about the state and is forward to a displacement receiver, which
finally identifies the input state by using feedback to adjust a reference
field. Numerical simulation results show that for 16-QAM, the hybrid receiver
could outperform the standard quantum limit (SQL) with a reduced number of
codeword interval partitions and on-off detectors, which shows great potential
toward implementing the practical application.
