Improved Accuracy on Noisy Devices by Nonunitary Variational Quantum Eigensolver for Chemistry Applications

Area of Science:

• Quantum computing
• Computational chemistry
• Electronic structure theory

Background:

• Variational Quantum Eigensolver (VQE) is a leading quantum algorithm for electronic structure calculations.
• Current VQE methods face challenges with noisy quantum hardware and complex wave function ansatze.
• Strongly correlated electrons require advanced simulation techniques.

Purpose of the Study:

• To develop a modified VQE algorithm (nu-VQE) for improved electronic structure optimization.
• To incorporate a nonunitary operator, specifically the Jastrow factor, into the VQE framework.
• To enhance the accuracy and error mitigation capabilities of VQE on noisy quantum computers.

Main Methods:

• Proposed the nonunitary Variational Quantum Eigensolver (nu-VQE) algorithm.
• Integrated the Jastrow factor, inspired by Quantum Monte Carlo methods, as the nonunitary operator.
• Applied nu-VQE to prototypical molecular Hamiltonians.

Main Results:

• Achieved accurate ground-state energies for molecular Hamiltonians.
• Demonstrated the use of shallower quantum circuits compared to traditional VQE.
• Observed a significant error mitigation effect, reducing absolute energy errors by an order of magnitude.
• Required an increased number of measurements to compensate for the nonunitary operator.

Conclusions:

• The nu-VQE algorithm offers a promising approach for accurate electronic structure calculations on current noisy quantum hardware.
• The Jastrow factor integration simplifies the wave function ansatz and enhances VQE performance.
• nu-VQE provides a substantial improvement in energy accuracy and error reduction for quantum chemistry simulations.