PHYSICAL REVIEW B, v. 77, No. 16, Article no. 165124
We investigate the functional form of the order-parameter (two-point) correlation function in quantum critical phenomena. When broken particle-hole symmetry brings the dynamical critical exponent z=2, we find that the equal-time correlation function at criticality does not display a diverging correlation length. We illustrate our conclusions by Monte Carlo calculations of the quantum rotor model in d=2 space dimensions.