Quantum nondemolition measurement of microwave photons and phase destruction

Abstract

Both the measuring process - the collapse of the photon-number distribution resulting from repeated (nonresonant) interaction with atoms - and the phase decay associated with it are analysed in a systematic manner for the quantum nondemolition measurement scheme proposed by Brune et al. [Phys. Rev. Lett. 65 (1990) 976; Phys. Rev. A 45 (1992) 5193]. Instead of simulating numerically actual measurements, the evolution of appropriate measures defined as averages over the whole ensemble characteristic of the field is studied. Numerical results indicate that phase decay faithfully mirrors the field collapse with respect to its dependence on the relevant physical parameters.