  We probe the transition between superfluid and Bose glass phases using
quantum quenches of disorder in an ultracold atomic lattice gas that realizes
the disordered Bose-Hubbard model. Measurements of excitations generated by the
quench exhibit threshold behavior in the disorder strength indicative of a
phase transition. Ab-initio quantum Monte Carlo simulations confirm that the
appearance of excitations coincides with the equilibrium superfluid--Bose-glass
phase boundary at different lattice potential depths. By varying the quench
time, we demonstrate the disappearance of an adiabatic timescale compared with
microscopic parameters in the BG regime.

Quantum Gases;Disordered Systems and Neural Networks