ABSTRACT Accurate calculation of spin‐state energy gaps is central to spin chemistry. The novel Quantum Phase Difference Estimation (QPDE) algorithm enables direct computation of energy gaps on a quantum computer. However, the required quantum circuits are typically too deep for noisy intermediate‐scale quantum (NISQ) devices. In this study, as an initial step toward practical calculations for strongly correlated molecular multi‐spin systems, we applied QPDE to two‐ and three‐spin Heisenberg Hamiltonians with various geometries and coupling strengths, including symmetric, asymmetric, spin‐frustrated, and non‐frustrated configurations. We found that the quantum circuit for the time‐evolution operator achieves constant depth due to its match gate‐like structure, making it well‐suited for NISQ implementation. Proof‐of‐principle hardware demonstrations using an IBM quantum processor yielded 85%–96% accuracy in determining spin‐state energy gaps.
Paul et al. (Sat,) studied this question.