Quantum enhanced sensing of optomechanical system

With the advances in nanomechanical resonators in the past few years, the sensitivity of optomechanical system has been push so far that quantum noise becomes the dominant noise to be dealt with. Quantum enhanced sensing refers to various methods that can be used to fight against quantum noise. In this dissertation, several mechanisms and methods are experimentally demonstrated that can be used to surpass the sensitivity limit set by the quantum noise in optomechanical systems, pushing their sensing capability into untested realms of physics. In general, any precision optical measure is accompanied by optical induced disturbance to the measured object, which is referred to as back action. Here I experimentally demonstrate back action evasion of optical level detection in the classical regime. In addition, the quantum efficiency of split photodetection used for readout is investigated and a method for improvement is experimentally demonstrated. In the second part I focus on a nonlinear mechanical interferometer based on coupling two modes of a single nanomechanical string resonator for high precision sensing. I demonstrate non-linear parametric interaction resulting from periodic stretching of the devise frame. These interactions correlate the mechanical noise and mix the states to yield a lower noise floor. Lastly, I briefly go through the earlier work on experimental realization of a new technique (ultralow-voltage electron-beam lithography) to create large scale and complex 2D quantum devices in LAO/STO heterostructure that is 10 000x faster compared to the previously used conductive-AFM.