Quantum technologies promise to revolutionise the fields of computation, communication and sensing, but require precise control over large ensembles of quantum systemsa formidable challenge. Quantum computing, in particular, requires potentially millions of qubits able to interact in arbitrary combination. Graph statesthe predominant language of qubit entanglementenable the prevailing, measurementbased model of quantum computation, which increases scalability by reducing qubit interaction requirements to nearest neighbours. Meanwhile, optics has long been the test bed for quantum phenomena. Meanwhile, integrated optics contends in the race to build practical quantum computers, incorporating highperformance components with massive scalability.
The purpose of the thesis is to develop multiphoton capability in integrated optics for generating graph states, on the road to linear optical quantum computing. To do so, I will investigate current methods for generating graph states theoretically, numerically and experimentally.
In Chapter 2, I derive rules for the successful postselection of optical graph states, bringing to light severe limitations to the technique. I then combine these rules with MonteCarlo numerics to learn which graph states are accessible to every type of single photon source.I also identify optimal interferometers for the generation of graph states up to $8$ qubits which are feasible today. Then, in Chapters 3 and 4, I report on the first integrated device to generate an entangled state of fourphotons. The programmable chip generates, for the first time, both kinds of fourqubit graph state, and breaks the multiphoton barrier for integrated optics. Further, the device demonstrates highvisibility heralded HongOuMandel interference. Finally, in Chapter 5, I use local complementaionwhich traverses all locally equivalent graph statesto generate the orbits of every entanglement class of $n<10$ qubits. These achievements light the way to scalable graph state generation with photons, and eventually linear optical quantum computing.
Date of Award  7 May 2019 

Original language  English 

Awarding Institution   The University of Bristol


Supervisor  John G Rarity (Supervisor), Mark Thompson (Supervisor) & Joshua W Silverstone (Supervisor) 

 quantum optics
 quantum computing
 quantum computing architectures
 integrated optics
 silicon photonics
 photonics
 graph states
Generating Optical Graph States
Adcock, J. C. (Author). 7 May 2019
Student thesis: Doctoral Thesis › Doctor of Philosophy (PhD)