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Reducing unitary coupled cluster circuit depth by classical stochastic amplitude prescreening

Published version
Peer-reviewed

Type

Article

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Authors

Fitzpatrick, N 
Muñoz Ramo, D 

Abstract

Unitary Coupled Cluster (UCC) approaches are an appealing route to utilising quantum hardware to perform quantum chemistry calculations, as quantum computers can in principle perform UCC calculations in a polynomially scaling fashion, as compared to the exponential scaling required on classical computers. Current noisy intermediate scale quantum (NISQ) computers are limited by both hardware capacity in number of logical qubits and the noise introduced by the deep circuits required for UCC calculations using the Variational Quantum Eigensolver (VQE) approach. We present a combined classical--quantum approach where a stochastic classical UCC pre-processing step is used to determine the important excitations in the UCC ansatz. The reduced number of selected excitations are then used in a UCC-based VQE calculation. This approach gives a systematically improvable approximation, and we show that significant reductions in quantum resources can be achieved, with simulations on the CH2, N2 and N2H2 molecules giving sub-milliHartree errors.

Description

Keywords

quant-ph, quant-ph, physics.chem-ph

Journal Title

Physical Review Research

Conference Name

Journal ISSN

2643-1564
2643-1564

Volume Title

4

Publisher

American Physical Society (APS)
Sponsorship
Royal Society (RGF/EA/180055)
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