title: Calculating expectations with time-dependent perturbations in quantum Monte Carlo.
abstract: We show that a small perturbation periodic in imaginary time can be used to compute expectation values of nondifferential operators that do not commute with the Hamiltonian within the framework of quantum diffusion Monte Carlo. Some results for the harmonic oscillator and the helium atom are presented showing the validity of the proposed method.
authors.affiliation: Lawrence Livermore National Laboratory, Livermore, California 94550, USA.
authors.forename: M H
authors.initials: MH
authors.lastname: Kalos
authors.forename: F Arias
authors.initials: FA
authors.lastname: de Saavedra