EPJ Quantum Technol. (2015) 2: 13
https://doi.org/10.1140/epjqt/s40507-015-0026-0

Research

Improved mirror position estimation using resonant quantum smoothing

¹ School of Engineering and Information Technology, UNSW Australia, Canberra, ACT, 2600, Australia
² Centre for Quantum Computation & Communication Technology, Australian Research Council, Canberra, Australia
³ Department of Electrical and Computer Engineering, National University of Singapore, 4 Engineering Drive 3, Singapore, 117583, Singapore
⁴ Department of Physics, National University of Singapore, 2 Science Drive 3, Singapore, 117551, Singapore
⁵ Research School of Engineering, College of Engineering and Computer Science, Australian National University, Canberra, ACT, 2600, Australia

^* e-mail: t.wheatley@adfa.edu.au

Received: 26 February 2015
Accepted: 23 April 2015
Published online: 20 May 2015

Abstract

Quantum parameter estimation, the ability to precisely obtain a classical value in a quantum system, is very important to many key quantum technologies. Many of these technologies rely on an optical probe, either coherent or squeezed states to make a precise measurement of a parameter ultimately limited by quantum mechanics. We use this technique to theoretically model, simulate and validate by experiment the measurement and precise estimation of the position of a cavity mirror. In non-resonant systems, the achieved estimation enhancement from quantum smoothing over optimal filtering has not exceeded a factor two, even when squeezed state probes were used. Using a coherent state probe, we show that using quantum smoothing on a mechanically resonant structure driven by a resonant forcing function can result significantly greater improvement in parameter estimation than with non-resonant systems. In this work, we show that it is possible to achieve a smoothing improvement by a factor in excess of three times over optimal filtering. By using intra-cavity light as the probe we obtain finer precision than has been achieved with the equivalent quantum resources in free-space.