Finding symmetry-broken ground states with variational quantum algorithms

One of the most promising applications for near-term intermediate scale quantum computers (NISQ) is the preparation of the true ground state of strongly correlated electron systems. Besides the ground-state energy the properties of interest of the ground state are its broken symmetries and the corresponding phases of the system.

We study the preparation of broken symmetry ground states on a gate based quantum computer with different variational algorithms, including the variational Hamiltonian ansatz (VHA) with initial state preparation and extensions to the standard VHA.
The two-dimensional Hubbard model is used as a toy model, to compare the variational algorithms to each other and to exact diagonalisation.
To this end, we simulate the full algorithm including initialization and read-out running on a gate-based quantum computer. We use a hardware model based on the gates available in currently available quantum computers.