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DOE OSTI · 3010479

Thermal Weight Determination and Interstate Coupling in State-Averaged ADAPT-VQE

Grimsley, Harper R. [Emory Univ., Atlanta, GA (United States)] (ORCID:000000015672468X)·Evangelista, Francesco A. [Emory Univ., Atlanta, GA (United States)] (ORCID:0000000279176652)
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Abstract

Characterizing electronic thermal states at low temperatures is an important but challenging task in quantum chemistry and condensed matter physics, making it a prime candidate for a useful application in quantum computing. One of the most successful methods for state preparation on quantum computers is the Adaptive, Problem-Tailored (ADAPT) Variational Quantum Eigensolver (VQE), which has recently been generalized to treat excited states within a state-averaged framework as well as Gibbs states. In this work, we introduce Helmholtz-Optimized Thermal (HOT) ADAPT-VQE, an ancilla-free strategy for preparing Gibbs states that directly minimizes the Helmholtz free energy by targeting the dominant eigenstates of the thermal ensemble. We demonstrate the usefulness of HOT-ADAPT-VQE by predicting the free energy of two model systems with strongly correlated ground states: (1) the Fe 2+ cation in a magnetic field and (2) a [Cu 2 O 7 ] 10– fragment of the Mott insulator La 2 CuO 4 . Our results demonstrate that HOT-ADAPT-VQE significantly improves upon Gibbs-state estimates from multistate variants of ADAPT-VQE, often with substantially shallower quantum circuits, making it a promising candidate for thermal-state calculations.

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37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRYalgorithmscluster chemistrymathematical methodsquantum mechanicsthermodynamic properties

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Grimsley, Harper R. [Emory Univ., Atlanta, GA (United States)] (ORCID:000000015672468X), Evangelista, Francesco A. [Emory Univ., Atlanta, GA (United States)] (ORCID:0000000279176652). 2025-12-04. Thermal Weight Determination and Interstate Coupling in State-Averaged ADAPT-VQE. https://doi.org/10.1021/acs.jctc.5c01313

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