Work measurement in an optomechanical quantum heat engine

We analyze theoretically measurement schemes of the mean output work and its fluctuations in a recently proposed optomechanical quantum heat engine [Zhang, Phys. Rev. Lett. 112, 150602 (2014)PRLTAO0031-900710.1103/PhysRevLett.112.150602]. After showing that this work can be operationally determined by continuous measurements of the intracavity photon number, we discuss both dispersive and absorptive measurement schemes and analyze their back-action effects on the efficiency of the engine. Both measurements are found to reduce the efficiency of the engine, but their back-action is both qualitatively and quantitatively different. For dispersive measurements the efficiency decreases as a result of the mixing of photonic and phononic excitations, while for absorptive measurements, its reduction arises from photon losses due to the interaction with the quantum probe.