  Systems of disordered interacting bosons with particle-hole symmetry can
undergo a quantum phase transition between the superfluid phase and the Mott
glass phase which is a gapless incompressible insulator. We employ large-scale
Monte Carlo simulations of a two-dimensional site-diluted quantum rotor model
to investigate the properties of the superfluid density and the compressibility
at this transition. We find that both quantities feature power-law critical
behavior with exponents governed by generalized Josephson relations.
