Adaptive construction of shallower quantum circuits with quantum spin projection for fermionic systems

Understand

Quantum computing is a promising approach to harnessing strong correlation in molecular systems; however, current devices only allow for hybrid quantum-classical algorithms with a shallow circuit depth, such as the variational quantum eigensolver (VQE).

• In this study, we report the importance of the Hamiltonian symmetry in constructing VQE circuits adaptively.
• This treatment often violates symmetry, thereby deteriorating the convergence of fidelity to the exact solution, and ultimately resulting in deeper circuits.
• We demonstrate that symmetry-projection can provide a simple yet effective solution to this problem, by keeping the quantum state in the correct symmetry space, to reduce the overall gate operations.