  We present a worm sampling method for calculating one- and two-particle
Green's functions using continuous-time quantum Monte Carlo simulations in the
hybridization expansion (CT-HYB). Instead of measuring Green's functions by
removing hybridization lines from partition function configurations, as in
conventional CT-HYB, the worm algorithm directly samples the Green's function.
We show that worm sampling is necessary to obtain general two-particle Green's
functions which are not of density-density type and that it improves the
sampling efficiency when approaching the atomic limit. Such two-particle
Green's functions are needed to compute off-diagonal elements of
susceptibilities and occur in diagrammatic extensions of the dynamical mean
field theory and efficient estimators for the single-particle self-energy.
