Demonstration of the Generalized Kennedy Receiver as a Near Quantum-Optimal Measurement for the Discrimination of Weak Classical Optical States

We describe an experimental testbed demonstrating quantum measurements on a single spatio-temporal, polarization mode, photon-starved classical state of light. The measurements are designed to optimally discriminate between coherent and incoherent optical states at mean photon numbers n < 2. A narrow-linewidth, 780 nm laser is used to prepare a coherent state or a thermal state in a single spatio-temporal, polarization mode. Three measurement strategies are implemented for the discrimination problem: photon counting, shot-noise limited coherent detection, and the near-optimal, generalized Kennedy receiver. For each receiver type we present discrimination error probability measurements as a function of the mean photon number of the received optical state.