CONTRADICTION OF QUANTUM-MECHANICS WITH LOCAL HIDDEN-VARIABLES FOR QUADRATURE PHASE-AMPLITUDE MEASUREMENTS

We demonstrate a contradiction of quantum mechanics with local hidden variable theories for continuous quadrature phase amplitude (''positio n'' and ''momentum'') measurements. For any quantum state, this contra diction is lost for situations where the quadrature phase amplitude re sults are always macroscopically distinct. We show that for optical re alizations of this experiment, where one uses homodyne detection techn iques to perform the quadrature phase amplitude measurement, one has a n amplification prior to detection, so that macroscopic fields are inc ident on photodiode detectors. The high efficiencies of such detectors may open a way for a loophole-free test of local hidden variable theo ries.