Simulation of, and with, first generation quantum computers

Thesis

The year is 2022. Scientists and engineers inch ever closer to building a practical quantum computer. The excitement in the research community, that we might soon fulfil Feynman’s dream to leverage quantum mechanics in machines capable of exponentially quicker computation, is steadily growing. With promised revolutions in chemistry, condensed matter physics and machine learning, and an expected market of 1.8 billion USD by 2026, quantum computing fights for the spotlight amid international pandemics and climate catastrophe. But the journey ahead is not an easy one. Quantum computers, requiring precise control of extraordinarily delicate quantum systems, are unsurprisingly challenging to engineer and equally difficult to design. A demonstration of quantum advantage through the quantum solving of a practical problem faster than available classical means, remains a research ambition.

At the forefront of this research are classical computers: the machines which crunch the numbers in our calculations, which interface with our quantum experiments, and which render this very document. Without them, quantum computation would have remained a fanciful whim on Feynman’s chalkboard. Behind the rapidly growing repertoire of quantum algorithms lies an equally impressive and expanding corpus of classical simulation strategies.

This thesis is about utilising first generation quantum computers and predicting their behaviour using classical computers. It develops novel quantum algorithms to perform variational minimisation, Hamiltonian diagonalisation, and approximate circuit recompilation, all intendedly compatible with near-future machines. It also devises classical algorithms for efficiently simulating quantum variational algorithms, emulating quantum computers using high-performance supercomputing facilities, and showcases the author’s efforts in scientific software development. Incidentally, this thesis makes no direct use of current day quantum hardware facilities. We hope to convince the disappointed reader that such an endeavour is presently pointless.

Authors: Jones, T

• Type of award: DPhil
• Level of award: Doctoral
• Awarding institution: University of Oxford
• Language: English
• Keywords: quantum computing; scientific simulation; high-performance computing; software design; algorithms
• Subjects: Quantum computing; Algorithms; High performance computing