MEASUREMENT AND PREPARATION USING 2 PROBE MODES

We consider the simultaneous measurement of two conjugate variables by coupling the system of interest to two independent probe modes. Our m odel consists of linearly coupled boson modes that can be realized by quantum optical fields in the rotating-wave approximation. We approach the setup both as a device to extract observable information and to p repare an emerging quantum state. The initial states of the probe mode s and the coupling are utilized to optimize the operation in the vario us regimes. In contrast to the Arthurs and Kelly ideal scheme [Bell. S yst. Tech. J. 44, 725 (1965)], our more realistic coupling does not al low perfect operation but the ideal situations can be approximated clo sely. We discuss the conditions for maximum information transfer to th e probe modes, information extraction with minimum disturbance of the system mode, and optimal state preparation for subsequent measurements . The minimum disturbance operation can be made to approximate a nonde molition measurement, especially when the information is carried in on e quadrature component only. In the preparation mode, we find that the recording accuracy of the probe signals plays an essential role. We r estrict the discussion to the first and second moments only, but the m ethod can easily be generalized to any situation, Choosing all modes t o be in squeezed coherent states originally, we can carry out analytic al considerations; other cases can be treated numerically. The results are presented and discussed in detail as the paradigm of a class of r ealizable measurements.