Resource-Efficient Chemistry on Quantum Computers with the Variational Quantum Eigensolver and the Double Unitary...

Area of Science:

• Quantum chemistry
• Computational physics
• Quantum computing

Background:

• Quantum simulation algorithms for molecular electronic energies face resource limitations on noisy intermediate-scale quantum (NISQ) devices.
• The number of qubits required scales linearly with molecular basis size, limiting simulations of electron correlation.
• Accurate quantum simulations of chemical processes are crucial for advancing molecular modeling.

Purpose of the Study:

• To develop a method for enabling more realistic molecular simulations on NISQ computers.
• To address the qubit scaling challenge in quantum simulations of electron correlation.
• To effectively downfold correlation effects into a reduced active space.

Main Methods:

• Employed the double unitary coupled-cluster (DUCC) method for downfolding correlation effects.
• Utilized downfolding techniques to construct effective Hamiltonians for reduced-size active spaces.
• Combined downfolding with the variational quantum eigensolver for ground-state energy calculations.

Main Results:

• Demonstrated that effective Hamiltonians capture whole orbital space effects in small active spaces.
• Successfully solved for the ground-state energy of H2, Li2, and BeH2 using DUCC-reduced active spaces.
• Compared results with full configuration-interaction and high-level coupled-cluster reference calculations.

Conclusions:

• The DUCC downfolding technique effectively reduces resource requirements for quantum simulations.
• This approach enables more accurate and feasible quantum chemistry calculations on NISQ devices.
• The method shows promise for simulating complex molecular systems with high accuracy.