Quantum measurement apparatus with a squeezed reservoir: Control of decoherence and nonlocality in phase space

We propose a quantum measurement model where the environment is taken to be a squeezed reservoir. This kind of meter-environment coupling has a dramatic influence on the decoherence rate. Depending on the phase and the squeezing parameter the decoherence time can be enhanced or reduced arbitrarily. We derive the Wigner function for the system-meter state, and discuss its nonclassical features. Further, we test quantum nonlocality in phase space on the basis of coincidence measurements of the entangled system-meter scheme, and investigate the effect of a highly reduced decoherence rate. Surprisingly, in sharp contrast to popular notion, violations of the Bell inequality can be observed even when the meter has reached a macroscopic state.