Quantum chemistry is a promising application for noisy intermediate-scale quantum (NISQ) devices. However, quantum computers have thus far not succeeded in providing solutions to problems of real scientific significance, with algorithmic advances being necessary to fully utilize even the modest NISQ machines available today. We discuss a method of ground state energy estimation predicated on a partitioning of the molecular Hamiltonian into two parts: one that is noncontextual and can be solved classically, supplemented by a contextual component that yields quantum corrections obtained via a Variational Quantum Eigensolver (VQE) routine. This approach has been termed Contextual Subspace VQE (CS-VQE); however, there are obstacles to overcome before it can be deployed on NISQ devices. The problem we address here is that of the ansatz, a parametrized quantum state over which we optimize during VQE; it is not initially clear how a splitting of the Hamiltonian should be reflected in the CS-VQE ansätze. We propose a “noncontextual projection” approach that is illuminated by a reformulation of CS-VQE in the stabilizer formalism. This defines an ansatz restriction from the full electronic structure problem to the contextual subspace and facilitates an implementation of CS-VQE that may be deployed on NISQ devices. We validate the noncontextual projection ansatz using a quantum simulator and demonstrate chemically precise ground state energy calculations for a suite of small molecules at a significant reduction in the required qubit count and circuit depth.
Weaving, Tim, et al. "A Stabilizer Framework for the Contextual Subspace Variational Quantum Eigensolver and the Noncontextual Projection Ansatz." Journal of Chemical Theory and Computation, vol. 19, no. 3, Jan. 2023. https://doi.org/10.1021/acs.jctc.2c00910
Weaving, Tim, Ralli, Alexis, Kirby, William M., Tranter, Andrew, Love, Peter J., & Coveney, Peter V. (2023). A Stabilizer Framework for the Contextual Subspace Variational Quantum Eigensolver and the Noncontextual Projection Ansatz. Journal of Chemical Theory and Computation, 19(3). https://doi.org/10.1021/acs.jctc.2c00910
Weaving, Tim, Ralli, Alexis, Kirby, William M., et al., "A Stabilizer Framework for the Contextual Subspace Variational Quantum Eigensolver and the Noncontextual Projection Ansatz," Journal of Chemical Theory and Computation 19, no. 3 (2023), https://doi.org/10.1021/acs.jctc.2c00910
@article{osti_2470284,
author = {Weaving, Tim and Ralli, Alexis and Kirby, William M. and Tranter, Andrew and Love, Peter J. and Coveney, Peter V.},
title = {A Stabilizer Framework for the Contextual Subspace Variational Quantum Eigensolver and the Noncontextual Projection Ansatz},
annote = {Quantum chemistry is a promising application for noisy intermediate-scale quantum (NISQ) devices. However, quantum computers have thus far not succeeded in providing solutions to problems of real scientific significance, with algorithmic advances being necessary to fully utilize even the modest NISQ machines available today. We discuss a method of ground state energy estimation predicated on a partitioning of the molecular Hamiltonian into two parts: one that is noncontextual and can be solved classically, supplemented by a contextual component that yields quantum corrections obtained via a Variational Quantum Eigensolver (VQE) routine. This approach has been termed Contextual Subspace VQE (CS-VQE); however, there are obstacles to overcome before it can be deployed on NISQ devices. The problem we address here is that of the ansatz, a parametrized quantum state over which we optimize during VQE; it is not initially clear how a splitting of the Hamiltonian should be reflected in the CS-VQE ansätze. We propose a “noncontextual projection” approach that is illuminated by a reformulation of CS-VQE in the stabilizer formalism. This defines an ansatz restriction from the full electronic structure problem to the contextual subspace and facilitates an implementation of CS-VQE that may be deployed on NISQ devices. We validate the noncontextual projection ansatz using a quantum simulator and demonstrate chemically precise ground state energy calculations for a suite of small molecules at a significant reduction in the required qubit count and circuit depth.},
doi = {10.1021/acs.jctc.2c00910},
url = {https://www.osti.gov/biblio/2470284},
journal = {Journal of Chemical Theory and Computation},
issn = {ISSN 1549-9618},
number = {3},
volume = {19},
place = {United States},
publisher = {American Chemical Society},
year = {2023},
month = {01}}
Brookhaven National Laboratory (BNL), Upton, NY (United States)
Sponsoring Organization:
USDOE Office of Science (SC); Unitary Fund and the Engineering and Physical Sciences Research Council; National Science Foundation (NSF); European Commission; Engineering and Physical Sciences Research Council (EPSRC)
Grant/Contract Number:
SC0012704
OSTI ID:
2470284
Journal Information:
Journal of Chemical Theory and Computation, Journal Name: Journal of Chemical Theory and Computation Journal Issue: 3 Vol. 19; ISSN 1549-9618