Fig. 1
From: Optical backaction-evading measurement of a mechanical oscillator
Backaction-evading measurement. a Illustration of a cavity optomechanical system. Light in a cavity with optical resonance ωc and full linewidth κ (of which κi are intrinsic losses) is coupled to the position \(\hat x\) of a mechanical oscillator that has frequency Ωm and linewidth Γm. In a backaction-evading (BAE) measurement, the probe is amplitude-modulated at the mechanical frequency Ωm, coupling to the quadrature \(\hat X\). b Frequency space configuration slightly detuned from BAE measurement, where the probe is modulated at Ωm + δ. c Resulting power spectral density of the cavity output field for an oscillator in a thermal state (mean occupation \(\bar n\)), showing the asymmetric Stokes and anti-Stokes scattered sidebands, plus the heating due to QBA. d When tuning to the BAE scheme δ = 0, the two sidebands coalesce and the QBA is cancelled, see Eq. (1). The remaining imprecision noise \(\overline n _{{\mathrm{imp}}}\) can be arbitrarily reduced by increasing probe power
