Resource-Optimized Fermionic Local-Hamiltonian Simulation on a Quantum Computer for Quantum Chemistry

Journal Article · 25 July 2021 · Quantum

DOI: https://doi.org/10.22331/q-2021-07-26-509 · OSTI ID:1810201

Wang, Qingfeng ^[1]; Li, Ming  ^[2]; Monroe, Christopher ^[3]; Nam, Yunseong  ^[4]

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1. Chemical Physics Program and Institute for Physical Science and Technology, University of Maryland, College Park, MD 20742, USA
2. IonQ, College Park, MD 20740, USA
3. IonQ, College Park, MD 20740, USA, Joint Quantum Institute, Department of Physics, and Joint Center for Quantum Information and Computer Science, University of Maryland, College Park, MD 20742, USA
4. IonQ, College Park, MD 20740, USA, Department of Physics, University of Maryland, College Park, MD 20742, USA

The ability to simulate a fermionic system on a quantum computer is expected to revolutionize chemical engineering, materials design, nuclear physics, to name a few. Thus, optimizing the simulation circuits is of significance in harnessing the power of quantum computers. Here, we address this problem in two aspects. In the fault-tolerant regime, we optimize the $R_z$ and $\text{T gate}$ counts along with the ancilla qubit counts required, assuming the use of a product-formula algorithm for implementation. We obtain a savings ratio of two in the gate counts and a savings ratio of eleven in the number of ancilla qubits required over the state of the art. In the pre-fault tolerant regime, we optimize the two-qubit gate counts, assuming the use of the variational quantum eigensolver (VQE) approach. Specific to the latter, we present a framework that enables bootstrapping the VQE progression towards the convergence of the ground-state energy of the fermionic system. This framework, based on perturbation theory, is capable of improving the energy estimate at each cycle of the VQE progression, by about a factor of three closer to the known ground-state energy compared to the standard VQE approach in the test-bed, classically-accessible system of the water molecule. The improved energy estimate in turn results in a commensurate level of savings of quantum resources, such as the number of qubits and quantum gates, required to be within a pre-specified tolerance from the known ground-state energy. We also explore a suite of generalized transformations of fermion to qubit operators and show that resource-requirement savings of up to more than $20\mathrm{\%}$ , in small instances, is possible.

• Research Organization: Duke University, Durham, NC (United States)
• Sponsoring Organization: USDOE; USDOE Office of Science (SC), Basic Energy Sciences (BES)
• Grant/Contract Number: SC0019449
• OSTI ID: 1810201
• Journal Information: Quantum, Journal Name: Quantum Vol. 5; ISSN 2521-327X
• Publisher: Verein zur Forderung des Open Access Publizierens in den QuantenwissenschaftenCopyright Statement
• Country of Publication: Austria
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
Variational quantum eigensolver