  Dynamic nonlinear (cubic) susceptibility in quantum d-dimensional Ising spin
glass with short-range interactions is investigated on the basis of quantum
droplet model and quantum-mechanical nonlinear response theory. Nonlinear
response depends on the tunneling rate for a droplet which regulates the
strength of quantum fluctuations. It shows a strong dependence on the
distribution of droplet free energies and on the droplet length scale average.
Comparison with recent experiments on quantum spin glasses like disordered
dipolar quantum Ising magnet is discussed.
