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Title: Quantum state reconstruction and computation with mechanical networks
Author: Moore, Darren William
ISNI:       0000 0004 6498 5945
Awarding Body: Queen's University Belfast
Current Institution: Queen's University Belfast
Date of Award: 2017
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Networks of mechanical resonators embedded in the platform of optomechanics are studied in two quantum information contexts: quantum state reconstruction and measurement based quantum computation. The optomechanical setup considered consists of a harmonically interacting network of resonators one of which is coupled via radiation pressure to a resonant mode of a cavity electromagnetic field. We develop a protocol for reconstructing the state of the network from measurements on the output cavity field. An interaction profile tuned to a set of mechanical quadratures ensures that the cavity field carries a copy of the quadratures’ information. Homodyne detection of the output field provides measurement statistics directly linked to the statistics of the mechanical quadratures from which their marginals can be estimated and standard tomographic techniques applied, recovering the phase space distribution for the network. We provide a method for determining the interaction profiles required and analyse the effectiveness of the scheme for Gaussian states in the case of finite measurements. We also provide some further examples of state reconstruction in similar optomechanics settings. An equivalent setup is that in which the cavity field interacts simultaneously with a collection of non­interacting mechanical modes. Here we implement measurement based quantum computation, giving a summary of cluster state generation in optomechanics and providing a scheme for applying multimode Gaussian operations. Adapting QND measurements on movable mirrors we continuously monitor individual resonators in order to assess the feasibility of using indirect measurements for computation compared to projective measurements performed directly on the cluster. Using a linear cluster state of five modes and taking advantage of the decomposition of single-mode Gaussian operations into four steps, we perform a numerical assessment of a large array of experimental parameters, paring down the list until those that most significantly affect the outcome are distilled. These are the mechanical bath temperature, the mechanical dissipation rate and the cluster squeezing. They place strong restrictions on the experimental parameters in order to ensure high fidelities, with stronger requirements for more highly squeezed clusters. We conclude with a small discussion of currently available experimental settings and remarks on further research possibilities.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available