Quantum Enhanced Sensing of Optomechanical SystemsHao, Shan (2024) Quantum Enhanced Sensing of Optomechanical Systems. Doctoral Dissertation, University of Pittsburgh. (Unpublished)
AbstractWith the advances in nanomechanical resonators in the past few years, the sensitivity of optomechanical system has been pushed 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 the first part, I focus on optical lever detection. The optical lever is a centuries-old and widely used detection technique where the angle of reflected light is used to infer the tilting of a surface. It is as sensitive as interferometry, but its quantum limits have yet to be explored. In general, any precision optical measurement is accompanied by an optical force induced disturbance to the measured object, which is referred to as back action. Here we walk through the principle of back action evasion in optical lever detection and experimentally demonstrate it 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 modified nonlinear mechanical SU(1,1) interferometer based on coupling two modes of a single nanomechanical string resonator for high-precision phase sensing. We walk through the theory, simulation, and experiment demonstrating parametric amplification and beam splitter interaction resulting from periodic stretching of the device frame that modulates the stress of the string resonator. These interactions correlate the mechanical noise and mix the states to yield a lower noise floor. We also propose a protocol to make full use of the squeezing in the presence of read out noise. Lastly, I briefly go through the earlier work on the experimental realization of a new technique (ultra-low-voltage electron beam lithography) to create large-scale and complex two-dimensional quantum devices in LaAlO3/SrTiO3 heterostructure that is 10 000 faster compared to the previously used conductive atomic force microscopy. Share
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