QUANTUM-NON-DEMOLITION MEASUREMENT OF THE PHASE

The problem of the QND measurement of the phase of a linear quantum os cillator is analyzed. It is shown that by measuring the quadrature amp litude one can reach a resolution close to the fundamental limit in a narrow range of phase values. A new method of QND phase measurement is proposed and analyzed. This method is also based on the coordinate in teraction between the quantum object and the measuring device but is f ree from the limitation mentioned above. Several practical schemes of phase measurements are discussed.