School of Physics and Astrophysics

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Kia Manouchehri


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Start date

Feb 2003

Submission date

Kia Manouchehri

Thesis

Quantum Walks: Theory and Implementation

Summary

In this thesis we present a theoretical study of quantum walks, with a particular focus on the development of viable schemes concerned with their physical realisation. Ever since their introduction over a decade ago, quantum walks have been extensively explored for their non-intuitive dynamics which may hold the key to a new generation of quantum algorithms. This growing interest in the theoretical applications of quantum walks has been paralleled by a flurry of research into a more practical problem: how does one physically implement a quantum walk in the laboratory? We begin this thesis by first presenting an overview of the quantum walk theory, including some of its algorithmic applications. This is then followed by a comprehensive survey of numerous proposals for a physical implementation of quantum walks, underpinned by a wide range of quantum, classical and hybrid technologies. This review consequently highlights what has so far remained a major challenge for the quantum walk enthusiasts; a physical realization that is experimentally viable whilst remaining readily scalable and not limited to problems with specific connectivity criteria. It is precisely this challenge that we seek to examine in the remaining parts of this thesis. To this end we first show that any physical implementation of a continuous-time quantum walk must adopt a discretized position space, otherwise the rich dynamics of the quantum walk are reduced to the simple quantum evolution of a particle in free space. We then describe a solid state approach for implementing a coined quantum walk on a line where, the quantum walker, an electron, hops from site to site in an array of quantum dots, prompted by a series of control lasers. Finally we introduce a universal framework for implementing general quantum walks on arbitrarily complex graphs. We demonstrate the utility of this universal scheme by providing a detailed description of one specific design based on the spin-dependant transport of a Bose Einstein Condensate (BEC) trapped in a 2D optical lattice, driven by a sequence of control lasers.

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