Entangled coherent states

TLDR

A nonlinear Mach–Zehnder interferometer converts a pair of coherent states into an entangled superposition of nonorthogonal coherent states, starting from a semiclassical state with a positive Glauber–Sudarshan representation. The scheme directs each mode to a homodyne detector, with the interferometer’s nonlinearity generating the nonclassical state. Nonclassical intensity correlations at the homodyne detector outputs enable a test of local realism.

Abstract

The nonlinear Mach-Zehnder interferometer is presented as a device whereby a pair of coherent states can be transformed into an entangled superposition of coherent states for which the notion of entanglement is generalized to include nonorthogonal, but distinct, component states. Each mode is directed to a homodyne detector. We show that there exist nonclassical intensity correlations at the output ports of the homodyne detectors which facilitate a test of local realism. In contradistinction to previous optical schemes which test local realism, the initial state used here possesses a positive Glauber-Sudarshan representation and is therefore a semiclassical state. The nonlinearity itself is responsible for generating the nonclassical state.