  We introduce a variational wavefunction for many-body ground states that
involves imaginary time evolution with two different Hamiltonians in an
alternating fashion with variable time intervals. We successfully apply the
ansatz on the one- and two-dimensional transverse-field Ising model and
systematically study its scaling for the one-dimensional model at criticality.
We find the total imaginary time required scales logarithmically with system
size, in contrast to the linear scaling in conventional Quantum Monte Carlo. We
suggest this is due to unique dynamics permitted by alternating imaginary time
evolution, including the exponential growth of bipartite entanglement. For
generic models, the superior scaling of our ansatz potentially mitigates the
negative sign problem at the expense of having to optimize variational
parameters.
