Computational Investigations of the Lithium Superoxide Dimer Rearrangement on Noisy Quantum Devices

Area of Science:

• Quantum chemistry
• Computational chemistry
• Quantum computing applications

Background:

• Studying biradical systems in quantum chemistry is complex due to the multiconfigurational nature of wavefunctions.
• Accurate energy profiles are crucial for understanding chemical reactions and molecular properties.

Purpose of the Study:

• To compute the energy profile of the lithium superoxide dimer rearrangement, a process involving biradical species, using quantum computing methods.
• To establish guidelines for selecting active spaces in quantum computations for systems requiring numerous qubits.
• To assess and improve the accuracy of Variational Quantum Eigensolver (VQE) on current quantum hardware.

Main Methods:

• Utilized the Variational Quantum Eigensolver (VQE) algorithm on quantum simulators and actual quantum devices.
• Developed strategies for active space selection to manage qubit limitations.
• Employed readout mitigation and state tomography techniques to correct for noise and purify quantum states.

Main Results:

• VQE on a quantum simulator accurately reproduced results from full-configuration interaction (Full CI) for the selected active space.
• Initial calculations on a quantum device showed a deviation of approximately 39 mHa from exact values.
• Readout mitigation reduced the deviation to ~4 mHa, and state tomography further improved accuracy to ~2 mHa, achieving chemical accuracy.

Conclusions:

• VQE is a viable method for studying challenging biradical systems, even with qubit constraints.
• Active space selection is critical for efficient quantum computations on near-term devices.
• Error mitigation techniques like readout mitigation and state tomography are essential for obtaining chemically accurate results from quantum hardware.