THEORY OF QUANTUM-OPTICAL MEASUREMENTS WITH A PHASE-CONJUGATE MIRROR

We show theoretically that optical phase conjugation via four-wave mixing can satisfy the quantitative criteria [Holland et al., Phys. Rev. A 42, 2995 (1990)] for performing quantum nondemolition measurements of a signal field despite the fact that this measurement scheme introduces noise into the signal field and thus does not perform a true quantum nondemolition measurement. The criteria can be satisfied under conditions in which the vacuum field injected in the rear of the phase-conjugate mirror is quadrature squeezed. Using this measurement scheme, it is possible to obtain values of the total information transfer coefficient that are as large as those that can be achieved using quantum nondemolition measurements. © 1995 The American Physical Society.