Paul D Stevenson

Paul D Stevenson

Nuclear Physics & Quantum Computing

New preprint

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This week my student Lance, along with Jim Al-Khalili and me as supervisors, has uploaded a new preprint to the arXiv. The work is a simulated quantum computing implementation of the imaginary time evolution algorithm to drive a quantum system from an initial trial wave function to its ground state. It’s a direct mapping of the classical algorithm, and we are able to see by comparison that the quantum version works correctly. We’ve applied it to the case of nuclear density functional theory, implemented in the wave function representation (i.e. the Kohn-Sham representation). Ultimately the problem is then represented by the single particle wave functions making up the nucleus. We chose the simplest case - spherical helium-4 in which there is only a single unique wave function to have to worry about. As a follow-on, we are working on the next-simplest case, oxygen-16, in which the nuclear density is made of two wave functions, at least in the simplified nuclear model we are considering.

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Solving coupled non-linear differential equations on quantum computer

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This week, we (PhD student Lance, co-supervisor Jim, and me) have published a new paper on a method of solution of non-linear coupled Schrödinger equtions on quantum computer.
It’s the continuation of some previous work where we employed the quantum imaginary time method to solve nuclear density functional problems in a simple model. In the new work, we wanted to make the model more realistic and less simple, and this meant solving simultaneously for multiple single particle wave functions, each of which are subject to slightly different Schrödinger equations, but which couple together through a density-depedendent term. Rather than present this work as specifically a way to solve the nuclear physics problem, we decided to send it to a more general journal which was running a special issue on quantum computing technology in the hope of reaching a wider audience. I guess we will see if it gets widely read and cited, but the referee, at least, agreed that it was worth publishing, at least after a round of comments / updates. The paper does not yet have its final volume and article number designation, but is online at the EPJ Special Topics journal site.

A Comment on Li et al.

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A recent paper by Li et al. introduced a variance minimization quantum algorithm. As one of their examples, they took a much-used nuclear physics case: A one-body model of the deuteron. Unfortunately, their presentation was a bit problematic, so I wrote a comment to submit to the journal (Physica Scripta) to try to correct the record. The comment was rejected by the editor, so I present the comment here instead, for the record - link at end of post. I would have put it on the arXiv, but they don’t publish comments of papers unless those papers are in the arXiv.

New Paper in Phys. Lett. B

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A new paper appeared today in Physics Letters B, here, which features the work of now-graduated PhD student Iain Lee, on friction in heavy ion reactions. The reaction studied was 16O + 92Zr, prompted by a previous experimental study which suggested that the reaction mechanism was notably different to that of 16O + 90Zr because of the higher density of states caused by the two neutrons outside of the closed shell. I got involved in the calculations by providing some time-dependent Hartree-Fock calculations to see what this kind of microscopic approach said about the rate of developement of the neck during fusion. One unusual aspect of this paper is that it was submitted less than two weeks ago. The editors sent it out for review extremely quickly, and referee comments came back quickly. They were serious comments and the referee had clearly read the paper well, and was an expert in the area. My colleauge Alexis, who was the coresponding author, worked on the response straight away, and the editor and referee accepted the response, meaning that the paper was accepted within a week, and has since apperaed (as an uncorrected proof) today, less than two weeks since submission.
I have never experienced such a quick process in publishing a scientific research paper!