Adaptive optical phase estimation using time-symmetric quantum smoothing

Abstract

We present an experimental demonstration of quantum smoothing, a non causal version of quantum parameter estimation that has applications from gravitational wave detection to quantum key distribution. An existing technique for this type of parameter estimation is quantum filtering, which uses past observations only. The technique presented here is time-symmetric that uses past and future observations to obtain a more precise estimate. We couple this innovative estimation technique with an adaptive detection scheme to demonstrate an estimation of the optical phase of light measured to be 2.24 ± 0.14 times better than the standard quantum limit. This approaches our theoretically derived prediction of a mean square error improvement of 2√2 times over the standard quantum limit [1]. Show more