Computation of Molecular Spectra on a Quantum Processor with an ErrorResilient Algorithm
Harnessing the full power of nascent quantum processors requires the efficient management of a limited number of quantum bits with finite coherent lifetimes. Hybrid algorithms, such as the variational quantum eigensolver (VQE), leverage classical resources to reduce the required number of quantum gates. Experimental demonstrations of VQE have resulted in calculation of Hamiltonian ground states, and a new theoretical approach based on a quantum subspace expansion (QSE) has outlined a procedure for determining excited states that are central to dynamical processes. Here, we use a superconductingqubitbased processor to apply the QSE approach to the H _{2} molecule, extracting both ground and excited states without the need for auxiliary qubits or additional minimization. Further, we show that this extended protocol can mitigate the effects of incoherent errors, potentially enabling largerscale quantum simulations without the need for complex errorcorrection techniques.
 Authors:

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 Univ. of California, Berkeley, CA (United States). Quantum Nanoelectronics Lab., Dept. of Physics
 Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States). Computational Research Division
 Univ. of California, Berkeley, CA (United States). Quantum Nanoelectronics Lab., Dept. of Physics; Univ. of California, Berkeley, CA (United States). Center for Quantum Coherent Science; Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States). Materials Science Division
 Publication Date:
 Grant/Contract Number:
 AC0205CH11231
 Type:
 Published Article
 Journal Name:
 Physical Review. X
 Additional Journal Information:
 Journal Volume: 8; Journal Issue: 1; Related Information: © 2018 authors. Published by the American Physical Society. Published by the American Physical Society under the terms of the https://creativecommons.org/licenses/by/4.0/ Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.; Journal ID: ISSN 21603308
 Publisher:
 American Physical Society
 Research Org:
 Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
 Sponsoring Org:
 USDOE Office of Science (SC), Advanced Scientific Computing Research (ASCR) (SC21)
 Country of Publication:
 United States
 Language:
 English
 Subject:
 75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY
 OSTI Identifier:
 1420209
 Alternate Identifier(s):
 OSTI ID: 1434014
Colless, J. I., Ramasesh, V. V., Dahlen, D., Blok, M. S., KimchiSchwartz, M. E., McClean, J. R., Carter, J., de Jong, W. A., and Siddiqi, I.. Computation of Molecular Spectra on a Quantum Processor with an ErrorResilient Algorithm. United States: N. p.,
Web. doi:10.1103/PhysRevX.8.011021.
Colless, J. I., Ramasesh, V. V., Dahlen, D., Blok, M. S., KimchiSchwartz, M. E., McClean, J. R., Carter, J., de Jong, W. A., & Siddiqi, I.. Computation of Molecular Spectra on a Quantum Processor with an ErrorResilient Algorithm. United States. doi:10.1103/PhysRevX.8.011021.
Colless, J. I., Ramasesh, V. V., Dahlen, D., Blok, M. S., KimchiSchwartz, M. E., McClean, J. R., Carter, J., de Jong, W. A., and Siddiqi, I.. 2018.
"Computation of Molecular Spectra on a Quantum Processor with an ErrorResilient Algorithm". United States.
doi:10.1103/PhysRevX.8.011021.
@article{osti_1420209,
title = {Computation of Molecular Spectra on a Quantum Processor with an ErrorResilient Algorithm},
author = {Colless, J. I. and Ramasesh, V. V. and Dahlen, D. and Blok, M. S. and KimchiSchwartz, M. E. and McClean, J. R. and Carter, J. and de Jong, W. A. and Siddiqi, I.},
abstractNote = {Harnessing the full power of nascent quantum processors requires the efficient management of a limited number of quantum bits with finite coherent lifetimes. Hybrid algorithms, such as the variational quantum eigensolver (VQE), leverage classical resources to reduce the required number of quantum gates. Experimental demonstrations of VQE have resulted in calculation of Hamiltonian ground states, and a new theoretical approach based on a quantum subspace expansion (QSE) has outlined a procedure for determining excited states that are central to dynamical processes. Here, we use a superconductingqubitbased processor to apply the QSE approach to the H2 molecule, extracting both ground and excited states without the need for auxiliary qubits or additional minimization. Further, we show that this extended protocol can mitigate the effects of incoherent errors, potentially enabling largerscale quantum simulations without the need for complex errorcorrection techniques.},
doi = {10.1103/PhysRevX.8.011021},
journal = {Physical Review. X},
number = 1,
volume = 8,
place = {United States},
year = {2018},
month = {2}
}
Works referenced in this record:
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journal, March 1972
journal, March 1972
 Hehre, W. J.; Ditchfield, R.; Pople, J. A.
 The Journal of Chemical Physics, Vol. 56, Issue 5, p. 22572261