Quantum Dynamics In Strongly Driven Random Dipolar Magnets

The random dipolar magnet LiHoxY1-xF4 enters a strongly frustrated regime for small Ho3+ concentrations with x < 0.05. In this regime, the magnetic moments of the Ho3+ ions experience small quantum corrections to the common Ising approximation of LiHoxY1-xF4, which lead to a Z(2) -symmetry breaking and small, degeneracy breaking energy shifts between different eigenstates. Here we show that destructive interference between two almost degenerate excitation pathways burns spectral holes in the magnetic susceptibility of strongly driven magnetic moments in LiHoxY1-xF4. Such spectral holes in the susceptibility, microscopically described in terms of Fano resonances, can already occur in setups of only two or three frustrated moments, for which the driven level scheme has the paradigmatic Lambda shape. For larger clusters of magnetic moments, the corresponding level schemes separate into almost isolated many-body Lambda schemes, in the sense that either the transition matrix elements between them are negligibly small or the energy difference of the transitions is strongly off-resonant to the drive. This enables the observation of Fano resonances, caused by many-body quantum corrections to the common Ising approximation also in the thermodynamic limit. We discuss its dependence on the driving strength and frequency as well as the crucial role that is played by lattice dissipation.