New stochastic method for systems with broken time-reversal symmetry: 2D fermions in a magnetic field

We present a stochastic method able to deal with complex Hermitian Hamiltonians where time reversal invariance is broken explicitly. We fix the phase of the wave function and show that the equation for the modulus can be solved by quantum Monte Carlo techniques. Then, any choice for its phase provides a variational upper bound for the ground state energy of the system. We apply the fixed-phase method to the 2D electron gas in the presence of a magnetic field with generalized periodic boundary conditions, where we study the transition between an incompressible ν=1/m Laughlin liquid and a Wigner crystal.