Measuring nanomechanical motion with an imprecision below that at the standard quantum limit

In the past decade, impressive efforts have been powered in the field of optomechanics that is the study of the coupling between a light field and a mechanical degree of freedom, with the major aims of detecting the quantum zero-point motion fluctuations of a mechanical object, and studying the fundamental quantum measurement processes. Though having their own specificities, both aims require combining ultra-high sensitivity readout together with ultra-sensitive mechanical response, sharing for example the common condition to involve measurement schemes limited at a level better than that of the Standard Quantum Limit (SQL) [1]. Using optical readout, we demonstrate for the first time sub-SQL imprecision for nanomechanical motion at room temperature. By using a cavity optomechanical near-field coupling scheme with more than one order of magnitude improved optomechanical coupling coefficients [2] combined with homodyne detection we reach a room-temperature imprecision 3 dB below the SQL launching only 1 W of optical input power (see Fig. 1).