Quantum and Classical Glass Transitions in $\mathrm{LiHo}_x\mathrm{Y}_{1-x}\mathrm{F}_4$

When performed in the proper low field, low frequency limits, measurements of the dynamics and the nonlinear susceptibility in the model Ising magnet in transverse field, $\mathrm{LiHo}_x\mathrm{Y}_{1-x}\mathrm{F}_4$, prove the existence of a spin glass transition in both the classical and quantum limits for x = 0.167 and 0.198. The classical behavior tracks for the two concentrations, but the quantum glasses differ because of the competing effects of entangled spins and local random fields.