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Using copies can improve precision in continuous-time quantum computing

Bennett, Jemma; Callison, Adam; O’Leary, Tom; West, Mia; Chancellor, Nicholas; Kendon, Viv

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Jemma Bennett
PGR Student Doctor of Philosophy

Adam Callison

Tom O’Leary

Mia West


In the quantum optimisation setting, we build on a scheme introduced by Young et al (2013 Phys. Rev. A 88 062314), where physical qubits in multiple copies of a problem encoded into an Ising spin Hamiltonian are linked together to increase the logical system's robustness to error. We introduce several innovations that improve the error suppression of this scheme under a special model of control noise, designed to understand how limited precision could be overcome. First, we note that only one copy needs to be correct by the end of the computation, since solution quality can be checked efficiently. Second, we find that ferromagnetic links do not generally help in this 'one correct copy' setting, but anti-ferromagnetic links do help on average, by suppressing the chance of the same error being present on all of the copies. Third, we find that minimum-strength anti-ferromagnetic links perform best, by counteracting the spin-flips induced by the errors. We have numerically tested our innovations on small instances of spin glasses from Callison et al (2019 New J. Phys.21 123022), and we find improved error tolerance for three or more copies in configurations that include frustration. Interpreted as an effective precision increase, we obtain several extra bits of precision on average for three copies connected in a triangle. This provides proof-of-concept of a method for scaling quantum annealing beyond the precision limits of hardware, a step towards fault tolerance in this setting.


Bennett, J., Callison, A., O’Leary, T., West, M., Chancellor, N., & Kendon, V. (2023). Using copies can improve precision in continuous-time quantum computing. Quantum Science and Technology, 8(3), Article 035031.

Journal Article Type Article
Acceptance Date Jun 8, 2023
Online Publication Date Jul 3, 2023
Publication Date 2023-07
Deposit Date Aug 17, 2023
Publicly Available Date Aug 17, 2023
Journal Quantum Science and Technology
Publisher IOP Publishing
Peer Reviewed Peer Reviewed
Volume 8
Issue 3
Article Number 035031
Keywords Electrical and Electronic Engineering; Physics and Astronomy (miscellaneous); Materials Science (miscellaneous); Atomic and Molecular Physics, and Optics
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