Stochastic calculation of tunneling in systems with many degrees of freedom

A new method is presented for the stochastic solution of tunneling problems in quantum many-body systems. The primary practical problem of trapping in local minima of the action is overcome by extending the standard implementation of the Metropolis algorithm to include collective updates motivated by semiclassical instanton solutions. We demonstrate the accuracy of our method in the case of tunneling in one degree of freedom and apply it to a model many-fermion system in one spatial dimension which undergoes spontaneous symmetric fission