Ultraprecision quantum sensing and measurement based on nonlinear hybrid optomechanical systems containing ultracold atoms or atomic Bose–Einstein condensate

In this review, the authors study how a hybrid optomechanical system (OMS), in which a quantum micro- or nano-mechanical oscillator is coupled to the electromagnetic radiation pressure, consisting of an ensemble of ultracold atoms or an atomic Bose–Einstein condensate, can be used as an ultraprecision quantum sensor for measuring very weak signals. As is well-known in any precise quantum measurement, the competition between the shot noise and the backaction noise of measurement executes a limitation on the measurement precision which is the so-called standard quantum limit (SQL). In the case where the intensity of the signal is even lower than the SQL, one needs to perform an ultraprecision quantum sensing to beat the SQL. For this purpose, the authors review three important methods for surpassing the SQL in a hybrid OMS: (i) the backaction evading measurement of a quantum nondemolition variable of the system, (ii) the coherent quantum backaction noise cancelation, and (iii) the so-called parametric sensing, the simultaneous signal amplification, and added noise suppression below the SQL. Furthermore, the authors have shown in this article for the first time how the classical fluctuation of the driving laser phase, the so-called laser phase noise, affects the power spectrum of the output optical field in a standard OMS and induces an additional impression noise which makes the total system noise increase above the SQL. Also, for the first time in this review it has been shown that in the standard OMSs, it is impossible to amplify the signal while suppressing the noise below the SQL simultaneously.