Protective measurement of the wave function of a single squeezed harmonic-oscillator state.

A scheme for the ‘‘protective measurement’’ @Phys. Rev. A 47, 4616 ~1993!# of the wave function of a squeezed harmonic-oscillator state is described. This protective measurement is shown to be equivalent to a measurement of an ensemble of states. The protective measurement, therefore, allows for a definition of the quantum wave function on a single system. Yet, this equivalency also suggests that both measurement schemes account for the epistemological meaning of the wave function only. The protective measurement requires a full a priori knowledge of the measured state. The intermediate cases, in which only partial a priori information is given, are also discussed.