On The Quantum Information Of Photons
: Entanglement And Distinguishability In Linear Optics

  • Stasja Stanisic

Student thesis: Doctoral ThesisDoctor of Philosophy (PhD)

Abstract

Research into the design and development of quantum devices has gained significant traction in recent years. As classical technologies are pushed ever closer to the limit of their capabilities, the need for the realisation of quantum devices increases. Through a combination of promising theoretical results and engineering advances, realisation of quantum technologies is becoming possible. A platform used for development of many of these quantum technologies is linear optics. Unfortunately, there are still significant engineering challenges to overcome in order to build relevant devices, from metrology to linear optical quantum computing (LOQC). Luckily, we can alleviate the pressure on developing engineering solutions, by examining and improving the theory behind some of the major challenges.

Firstly, optimizing the generation of entanglement necessary for the smallest building block of a measurement-based quantum computer, the contending LOQC platform, would help with scaling of resources. We offer numerical evidence of optimality of the current scheme for generation of Bell pairs. We also find limits to entanglement generation more generally between two subsets of modes with no encoding present, using only linear optical components. Beyond the implications for engineering of entanglement generation, these general results raise interesting foundational questions. Secondly, we present a framework for examining the distinguishability of particles. We take a quantum information inspired approach by giving a bipartite model where distinguishability can arise as correlation with an environment. This offers a new formalism for distinguishable states and uncovers intriguing observations of the underlying dynamics of bosonic behaviour. We use this model to generalize Hong-Ou-Mandel interference as unambiguous state discrimination, giving analytical and numerical evidence for optimal interferometers with a small number of photons. This demonstrates the utility with which standard quantum information tools can be applied within this new framework. We conclude with a discussion of some observations and directions for possible future research.
Date of Award12 May 2020
Original languageEnglish
Awarding Institution
  • The University of Bristol
SupervisorNoah Linden (Supervisor) & Peter Turner (Supervisor)

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