Efficient ground state preparation in variational quantum eigensolver with symmetry breaking layers

Variational quantum eigensolver (VQE) that solves the ground state of a Hamiltonian is a promising application of noisy intermediate-scale quantum devices. The quantum alternating operator Ansatz (QAOA) is one of the most widely studied Ansatze for this purpose and solves many Hamiltonians reliably. However, because of inherited symmetries from the Hamiltonian, the QAOA is not necessarily good at solving problems with symmetry broken nature. In this paper, we propose a variational Ansatz with symmetry breaking layers for solving those systems. Notably, our Ansatz finds a constant-depth circuit for solving a symmetry broken ground state which is impossible for the QAOA. We also propose a simple learning technique that can choose a particular symmetry broken state among degenerate ground states.