Approximate quantum circuit compilation for proton-transfer kinetics on quantum processors.

Area of Science:

• Quantum Chemistry
• Computational Chemistry
• Chemical Physics

Background:

• Proton transfer reactions are crucial in chemistry and biology.
• Quantum effects like tunneling significantly impact reaction rates.
• Classical computational methods struggle with large systems for these quantum effects.

Purpose of the Study:

• To extend and benchmark a quantum computing framework for proton transfer reactions.
• To assess the feasibility of calculating accurate energy barriers on current quantum devices.
• To investigate quantum mechanical treatment of protons using the Nuclear-Electronic Orbital (NEO) formalism.

Main Methods:

• Utilized the ADAPT-VQE algorithm with frozen natural orbital approximation to build quantum circuits.
• Employed adaptive approximate quantum compiling to optimize circuit depth and fidelity.
• Transpiled circuits for the ibm_pittsburgh quantum device and simulated with realistic noise models.

Main Results:

• Computed energy barriers and delocalized proton densities for malonaldehyde.
• Demonstrated that refined and compressed circuits preserve essential quantum features.
• Shallow circuits (AQC-low) qualitatively reproduced proton localization, near current hardware limits.
• Deeper circuits (AQC-high) achieved higher fidelity to reference barrier heights (1.6 mHa error).

Conclusions:

• Quantum computing offers a viable path for studying quantum effects in proton transfer.
• Shallow quantum circuits show promise for near-term hardware feasibility.
• Accurate quantum mechanical treatment of protons is achievable, though challenges remain for precise rate constant prediction.