2022 Prize Winner - Blayney Walshe

The Ian Snook prize will assist Blayney and his family as they move from Melbourne, Australia to Toronto, Canada, where Blayney will continue his research into continuous-variable quantum computing by taking a full-time position with Xanadu in June of 2023.

For the duration of his PhD, Blayney's research focused on the study of continuous variable quantum computing. Quantum computers aim to solve many problems, from materials and drug modelling to weather and financial trends. Using a principle of quantum mechanics, the superposition, it is expected that certain problems can be done quicker or more efficiently with a quantum computer when compared to classical computing. Contrary to popular belief, quantum computers do not use a superposition to solve for various outcomes "at the same time", but they manipulate a superposition of all possible solutions to a problem, reducing the likelihood that the quantum computer will output an incorrect solution and increasing the likelihood that it will output the correct solution.

Continuous variable quantum computing uses entangled modes of light encoded with logical qubits as the resource with which to drive computations. The benefits of this method, over devices that contain physical qubits, is that it is possible to create extremely large cluster states with existing technology, and they can operate at room temperature, rather than requiring temperatures near absolute zero. A drawback, however, is that these modes of light have an inherent noise that makes it difficult to distinguish between the two logical states of an encoded qubit.

Blayney's PhD research focuses on resolving this problem by examining the noise and its effects more closely, examining how 'good' physical cluster states need to be in order to be fault tolerant (so that inevitable errors can be corrected, and reduced, rather than amplified by the error-correction process), and proposing error correction methods for use with cluster states in practice.

In 2020, Blayney interned at Xanadu Quantum Technologies Inc., researching alternate cluster state construction methods for use with their quantum computing architecture. There, he built a working relationship that continued throughout his PhD.

As of writing, Blayney has published 3 first-author papers, with 2 more in preparation, and is listed as an inventor on a patent relating to his work with Xanadu. www.qurmit.org for more information.

Blayney W. Walshe, Rafael N. Alexander, Nicolas C. Menicucci, and Ben Q. Baragiola. Streamlined quantum computing with macronode cluster states, PRA 104, 062427 (2021). In this work, we demonstrate a more efficient use of the quad-rail lattice macronode cluster state resource. We show a Clifford gate and macronode error correction can be performed in a single measurement step and provide the required measurement angles to perform the Clifford generating set.

Blayney W. Walshe, Ben Q. Baragiola, Rafael N. Alexander, and Nicolas C. Menicucci. Continuous-variable gate teleportation and bosonic-code error correction, PRA 102, 062411 (2020). This article interprets a major physical resource for continuous-variable quantum computation, the macronode wire, as a series of gate teleportations. We define one such teleportation using arbitrary states to enable our definition to be used to analyse many types of non-Gaussian gates. We then apply this general result to GKP error correction on macronode-based cluster states—a previously open problem.

Blayney W. Walshe, Lucas J. Mensen, Ben Q. Baragiola, and Nicolas C. Menicucci. Robust fault tolerance for continuous-variable cluster states with excess antisqueezing, PRA 100, 010301(R) (2019). In this paper, we apply an additional source of noise to an established continuous-variable fault- tolerance result and show that this noise source has no effect upon the result. This is important for experimentalists seeking to mitigate the various sources of noise in their physical systems.