Results of measurement on a harmonic oscillator using a back-action-evading scheme

The authors report the preliminary results obtained by using a Quantum non Demolition Scheme (QND) to make observations in a classical harmonic oscillator. In principle, QND schemes, which can be referred to as allowing an arbitrary precision of observations in a harmonic oscillator, can completely circumvent the effects of back-action. Classically this suggests that they should be able to beat the amplifier limit. (Auth.)