Orbital-optimized pair-correlated electron simulations on trapped-ion quantum computers

Variational quantum eigensolvers (VQE) are among the most promising approaches for solving electronic structure problems on near-term quantum computers. A critical challenge for VQE in practice is that one needs to strike a balance between the expressivity of the VQE ansatz versus the number of quan...

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Bibliographic Details
Published in:npj quantum information 2023-06, Vol.9 (1), p.60-9, Article 60
Main Authors: Zhao, Luning, Goings, Joshua, Shin, Kyujin, Kyoung, Woomin, Fuks, Johanna I., Kevin Rhee, June-Koo, Rhee, Young Min, Wright, Kenneth, Nguyen, Jason, Kim, Jungsang, Johri, Sonika
Format: Article
Language:English
Subjects:
639/638/563/758
639/766/483/3926
Classical and Quantum Gravitation
Computers
Physics
Physics and Astronomy
Quantum Computing
Quantum Field Theories
Quantum Information Technology
Quantum Physics
Relativity Theory
Spintronics
String Theory
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Summary:Variational quantum eigensolvers (VQE) are among the most promising approaches for solving electronic structure problems on near-term quantum computers. A critical challenge for VQE in practice is that one needs to strike a balance between the expressivity of the VQE ansatz versus the number of quantum gates required to implement the ansatz, given the reality of noisy quantum operations on near-term quantum computers. In this work, we consider an orbital-optimized pair-correlated approximation to the unitary coupled cluster with singles and doubles (uCCSD) ansatz and report a highly efficient quantum circuit implementation for trapped-ion architectures. We show that orbital optimization can recover significant additional electron correlation energy without sacrificing efficiency through measurements of low-order reduced density matrices (RDMs). In the dissociation of small molecules, the method gives qualitatively accurate predictions in the strongly-correlated regime when running on noise-free quantum simulators. On IonQ’s Harmony and Aria trapped-ion quantum computers, we run end-to-end VQE algorithms with up to 12 qubits and 72 variational parameters—the largest full VQE simulation with a correlated wave function on quantum hardware. We find that even without error mitigation techniques, the predicted relative energies across different molecular geometries are in excellent agreement with noise-free simulators.
ISSN:2056-6387
2056-6387
DOI:10.1038/s41534-023-00730-8