Hyperfine Coupling Constants on Quantum Computers: Performance, Errors, and Future Prospects

Area of Science:

• Quantum computing
• Computational chemistry
• Quantum physics

Background:

• Electron spin resonance (ESR) is crucial for molecular structure determination.
• Calculating isotropic hyperfine coupling constants (HFCs) is computationally intensive.
• Quantum computing offers a potential new paradigm for molecular simulations.

Purpose of the Study:

• To implement and compute ESR isotropic HFCs on quantum hardware for the first time.
• To validate the quantum approach using small radical and cation test cases.
• To assess the efficacy of error mitigation strategies in quantum computations.

Main Methods:

• Integration of the qubit-ADAPT algorithm with unrestricted orbital optimization.
• Utilizing an active space framework for molecular property calculations.
• Employing advanced error mitigation, suppression, and postselection techniques, including ansatz-based readout and gate error mitigation.

Main Results:

• Successful computation of HFCs for hydroxyl radical (OH•), nitric oxide (NO•), and triplet hydroxyl cation (OH+).
• Quantum hardware results show strong agreement with classical unrestricted complete active space self-consistent field (U-CASSCF) calculations.
• Demonstrated the necessity and effectiveness of multimethod error strategies for accurate quantum results.

Conclusions:

• This work represents a significant advancement in applying quantum computing to chemically relevant molecular properties.
• The developed quantum approach, coupled with robust error mitigation, is viable for calculating HFCs.
• Highlights the critical role of error handling in achieving reliable results on noisy intermediate-scale quantum (NISQ) devices.