Quantum Computing Approach to Atomic and Molecular Three-Body Systems

TL;DR

This paper demonstrates high-precision quantum simulations of three-body atomic and molecular systems using an efficient, gradient-free variational approach, enabling accurate results on NISQ devices and potential for studying complex effects.

Contribution

The authors introduce NI-DUCC-VQE, a novel quantum algorithm that efficiently simulates three-body systems with high accuracy and scalability, avoiding barren plateaus and gradient evaluations.

Findings

Achieved energy errors as low as 10^{-11} a.u.

Demonstrated rapid convergence with only a few thousand function evaluations.

Validated the approach on four different three-body systems.

Abstract

We present high-precision quantum computing simulations of three-body atoms (He, H$^-$) and molecules (H$_2^+$, HD$^+$), the latter being studied beyond the Born-Oppenheimer approximation. The Non-Iterative Disentangled Unitary Coupled Cluster Variational Quantum Eigensolver (NI-DUCC-VQE) [M. Haidar et al., Quantum Sci. Technol. 10, 025031 (2025)] is used. By combining a first-quantized Hamiltonian with a Minimal Complete Pool (MCP) of Lie-algebraic excitations, we construct a compact ansatz with a gradient-independent construction, avoiding costly gradient evaluations and yielding efficient computational scaling with both basis size and electron number. It avoids barren plateaus and enables rapid convergence, achieving energy errors as low as 10$^{-11}$ a.u. with state fidelities only limited by arithmetic precision in only a few thousand function evaluations in all four systems. These results make three-body atoms and molecules excellent candidates for benchmarking and testing on current Noisy Intermediate-Scale Quantum (NISQ) devices. Further, our approach can be extended to more complex systems with larger basis sets, taking advantage of the efficient scaling of qubit requirements to study electronic correlations and non-adiabatic effects with high precision. We also demonstrate the applicability of NI-DUCC-VQE for simulating higher-order effects such as relativistic corrections and hyperfine interactions.