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Chemical control of spin–lattice relaxation to discover a room temperature molecular qubit

Amdur, M. Jeremy and Mullin, Kathleen R. and Waters, Michael J. and Puggioni, Danilo and Wojnar, Michael K. and Gu, Mingqiang and Sun, Lei and Oyala, Paul H. and Rondinelli, James M. and Freedman, Danna E. (2022) Chemical control of spin–lattice relaxation to discover a room temperature molecular qubit. Chemical Science, 13 (23). pp. 7034-7045. ISSN 2041-6520. PMCID PMC9200133. doi:10.1039/d1sc06130e.

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The second quantum revolution harnesses exquisite quantum control for a slate of diverse applications including sensing, communication, and computation. Of the many candidates for building quantum systems, molecules offer both tunability and specificity, but the principles to enable high temperature operation are not well established. Spin–lattice relaxation, represented by the time constant T₁, is the primary factor dictating the high temperature performance of quantum bits (qubits), and serves as the upper limit on qubit coherence times (T₂). For molecular qubits at elevated temperatures (>100 K), molecular vibrations facilitate rapid spin–lattice relaxation which limits T₂ to well below operational minimums for certain quantum technologies. Here we identify the effects of controlling orbital angular momentum through metal coordination geometry and ligand rigidity via π-conjugation on T₁ relaxation in three four-coordinate Cu²⁺ S = ½ qubit candidates: bis(N,N′-dimethyl-4-amino-3-penten-2-imine) copper(II) (Me₂Nac)₂ (1), bis(acetylacetone)ethylenediamine copper(II) Cu(acacen) (2), and tetramethyltetraazaannulene copper(II) Cu(tmtaa) (3). We obtain significant T₁ improvement upon changing from tetrahedral to square planar geometries through changes in orbital angular momentum. T₁ is further improved with greater π-conjugation in the ligand framework. Our electronic structure calculations reveal that the reduced motion of low energy vibrations in the primary coordination sphere slows relaxation and increases T₁. These principles enable us to report a new molecular qubit candidate with room temperature T₂ = 0.43 μs, and establishes guidelines for designing novel qubit candidates operating above 100 K.

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URLURL TypeDescription CentralArticle Information structure data Itemstructures of optimized molecules used in density-functional theory calculations
Waters, Michael J.0000-0001-6425-4331
Puggioni, Danilo0000-0002-2128-4191
Wojnar, Michael K.0000-0003-2556-7014
Gu, Mingqiang0000-0002-2889-2202
Sun, Lei0000-0001-8467-6750
Oyala, Paul H.0000-0002-8761-4667
Rondinelli, James M.0000-0003-0508-2175
Freedman, Danna E.0000-0002-2579-8835
Additional Information:© 2022 The Author(s). Published by the Royal Society of Chemistry. This article is licensed under a Creative Commons Attribution 3.0 Unported Licence. Received 4th November 2021. Accepted 16th May 2022. All publication charges for this article have been paid for by the Royal Society of Chemistry. We are grateful for the intellectual discussions and scientific guidance provided by H. Mao, M. Krzyaniak, Drs K. Collins, M. Fataftah, S. Coste and S. v. Kugelgen. We thank H. Park for assistance with Raman spectroscopy. This work was supported by the U.S. Department of Energy, Office of Science, Basic Energy Sciences under award DE-SC0019356. M. J. A. thanks QISE-NET for support of the collaboration with Argonne National Laboratory. Mass spectrometry, NMR spectroscopy, and crystallography made use of the IMSERC at Northwestern University, which has received support from the NSF (CHE-1048773), Soft and Hybrid Nanotechnology Experimental (SHyNE) Resource (NSF ECCS-1542205), the state of Illinois, and the International Institute for Nanotechnology (IIN). The Caltech EPR facility acknowledges support from the NSF (MRI grant 1531940) and the Dow Next Generation Educator Fund. This work used resources at the National Energy Research Scientific Computing Center, a DOE Office of Science User Facility supported by the Office of Science of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231. Argonne National Laboratory's contribution is based upon work supported by Laboratory Directed Research and Development (LDRD) funding from Argonne National Laboratory, provided by the Director, Office of Science, of the U.S. Department of Energy under Contract No. DE-AC02-06CH11357. Data availability. Crystallographic information can be found in the ICSD. The structures of optimized molecules used in density-functional theory calculations can be found at: Author contributions. Conceptualization: M. J. A., J. M. R., and D. E. F.; investigation and formal analysis: M. J. A., K. R. M., M. J. W., D. P. and M. K.W.; resources: L. S. and P. H. O.; visualization: M. J. A. and M. J. W.; supervision: D. E. F. and J. R. M.; all authors contributed to writing the manuscript. There are no conflicts to declare.
Funding AgencyGrant Number
Department of Energy (DOE)DE-SC0019356
International Institute for Nanotechnology (IIN)UNSPECIFIED
State of IllinoisUNSPECIFIED
Dow Next Generation Educator FundUNSPECIFIED
Department of Energy (DOE)DE-AC02-05CH11231
Argonne National LaboratoryUNSPECIFIED
Department of Energy (DOE)DE-AC02-06CH11357
Royal Society of ChemistryUNSPECIFIED
Issue or Number:23
PubMed Central ID:PMC9200133
Record Number:CaltechAUTHORS:20220705-671808000
Persistent URL:
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:115306
Deposited By: George Porter
Deposited On:08 Jul 2022 00:25
Last Modified:08 Jul 2022 00:25

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