https://doi.org/10.1140/epjp/s13360-025-06876-y
Regular Article
Trapped ion quantum hardware demonstration of energy calculations using a multireference unitary coupled cluster ansatz: application to the BeH
insertion problem
1
Centre for Quantum Engineering, Research and Education, TCG Crest, 700091, Kolkata, India
2
Department of Physics, IIT Tirupati, 517619, Chindepalle, Andhra Pradesh, India
3
Graduate School of Science and Technology, Keio University, 7-1 Shinkawasaki, Saiwai-ku, 212-0032, Kawasaki, Kanagawa, Japan
4
Quantum Computing Center, Keio University, 3-14-1 Hiyoshi, Kohoku-ku, 223-8522, Yokohama, Kanagawa, Japan
5
Keio University Sustainable Quantum Artificial Intelligence Center (KSQAIC), Keio University, 2-15-45 Mita, Minato-ku, Tokyo, Japan
6
Qilimanjaro Quantum Tech, Carrer de Veneçuela, 74, Sant Martí, 08019, Barcelona, Spain
7
Universitat Politècnica de Catalunya, Carrer de Jordi Girona, 3, 08034, Barcelona, Spain
8
Academy of Scientific and Innovative Research (AcSIR), 201002, Ghaziabad, India
a
srinivasaprasannaa@gmail.com
Received:
9
April
2025
Accepted:
17
September
2025
Published online:
27
September
2025
In this study, we employ the variational quantum eigensolver algorithm with a multireference unitary coupled cluster ansatz to report the ground state energy of the BeH molecule in a geometry where strong correlation effects are significant. We consider the two most important determinants in the construction of the reference state for our ansatz. We remove redundancies in order to execute a redundancy-free calculation. In view of the currently available noisy quantum hardware, we carry out parameter optimization on a classical computer and measure the energy with optimized parameters on a quantum computer. Furthermore, in order to carry out our intended 12-qubit computation with error mitigation and post-selection on a noisy intermediate scale quantum era trapped ion hardware (the commercially available IonQ Forte-I), we perform a series of resource reduction techniques to a. decrease the number of two-qubit gates by 
(from 12243 to 20 two-qubit gates) relative to the unoptimized circuit, and b. reduce the number of measurements via the idea of supercliques, while losing 
in the obtained ground state energy relative to that computed classically for the same resource-optimized problem setting.
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© The Author(s), under exclusive licence to Società Italiana di Fisica and Springer-Verlag GmbH Germany, part of Springer Nature 2025
Springer Nature or its licensor (e.g. a society or other partner) holds exclusive rights to this article under a publishing agreement with the author(s) or other rightsholder(s); author self-archiving of the accepted manuscript version of this article is solely governed by the terms of such publishing agreement and applicable law.
