Browsing by Author "Motta, Mario"

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    Bridging physical intuition and hardware efficiency for correlated electronic states: the local unitary cluster Jastrow ansatz for electronic structure
    (Royal Society of Chemistry, 2023) Motta, Mario; Sung, Kevin J.; Whaley, K. Birgitta; Head-Gordon, Martin; Shee, James
    A prominent goal in quantum chemistry is to solve the molecular electronic structure problem for ground state energy with high accuracy. While classical quantum chemistry is a relatively mature field, the accurate and scalable prediction of strongly correlated states found, e.g., in bond breaking and polynuclear transition metal compounds remains an open problem. Within the context of a variational quantum eigensolver, we propose a new family of ansatzes which provides a more physically appropriate description of strongly correlated electrons than a unitary coupled cluster with single and double excitations (qUCCSD), with vastly reduced quantum resource requirements. Specifically, we present a set of local approximations to the unitary cluster Jastrow wavefunction motivated by Hubbard physics. As in the case of qUCCSD, exactly computing the energy scales factorially with system size on classical computers but polynomially on quantum devices. The local unitary cluster Jastrow ansatz removes the need for SWAP gates, can be tailored to arbitrary qubit topologies (e.g., square, hex, and heavy-hex), and is well-suited to take advantage of continuous sets of quantum gates recently realized on superconducting devices with tunable couplers. The proposed family of ansatzes demonstrates that hardware efficiency and physical transparency are not mutually exclusive; indeed, chemical and physical intuition regarding electron correlation can illuminate a useful path towards hardware-friendly quantum circuits.
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    Towards the Solution of the Many-Electron Problem in Real Materials: Equation of State of the Hydrogen Chain with State-of-the-Art Many-Body Methods
    (American Physical Society, 2017) Motta, Mario; Ceperley, David M.; Chan, Garnet Kin-Lic; Gomez, John A.; Gull, Emanuel; Guo, Sheng; Jiménez-Hoyos, Carlos A.; Lan, Tran Nguyen; Li, Jia; Ma, Fengjie; Millis, Andrew J.; Prokof’ev, Nikolay V.; Ray, Ushnish; Scuseria, Gustavo E.; Sorella, Sandro; Stoudenmire, Edwin M.; Sun, Qiming; Tupitsyn, Igor S.; White, Steven R.; Zgid, Dominika; Zhang, Shiwei
    We present numerical results for the equation of state of an infinite chain of hydrogen atoms. A variety of modern many-body methods are employed, with exhaustive cross-checks and validation. Approaches for reaching the continuous space limit and the thermodynamic limit are investigated, proposed, and tested. The detailed comparisons provide a benchmark for assessing the current state of the art in many-body computation, and for the development of new methods. The ground-state energy per atom in the linear chain is accurately determined versus bond length, with a confidence bound given on all uncertainties.