QUANTUM-NONDEMOLITION MEASUREMENT OF THE VIBRATIONAL-ENERGY OF A TRAPPED ION

A quantum-nondemolition (QND) measurement of the vibrational energy of a trapped ion may be made by placing it at a node of a cavity optical standing wave. In certain parameter regimes there is a backaction eva ding coupling between the ion's vibrational energy eigenstates and the coherent states of the cavity field. This facilitates a QND measureme nt of the ion trap state via a homodyne measurement on the cavity outp ut field. This scheme has the advantage that the required measurements minimally disturb the ion.