Optimum decision scheme with a unitary control process for binary quantum-state signals

A scheme for distinguishing between binary signals of nonorthogonal coherent states with the minimum average error is proposed. In contrast to the well-known Dolinar scheme, it does not use a feedback process, Instead, it achieves the same minimum error bound by only unitary transformations and photon number counting. It is shown that the required transformation should produce the appropriate Schrodinger-cat states. An example of the Hamiltonian generating such a process is derived from a multiphoton nonlinear optical process.