  The unitary coupled cluster (UCC) ansatz is a promising tool for achieving
high-precision results using the variational quantum eigensolver (VQE)
algorithm in the NISQ era. However, results on quantum hardware are thus far
very limited and simulations have only accessed small system sizes. We advance
the state of the art of UCC simulations by utilizing an efficient sparse
wavefunction circuit solver and studying systems up to 64 qubits. Here we
report results obtained using this solver that demonstrate the power of the UCC
ansatz and address pressing questions about optimal initial parameterizations
and circuit construction, among others. Our approach enables meaningful
benchmarking of the UCC ansatz, a crucial step in assessing the utility of VQE
for achieving quantum advantage.
