Tunable Quantum Dynamics in a Disordered Magnet

Quantum memories depend on maintaining coherence in minimally-interacting qubits. In an attempt to engineer such memories, we decouple coherent many-body excitations from their environment in the dilute Ising magnet LiHo0.045Y0.955F4 by driving the system into a non-linear regime with a Floquet drive. In this material, clusters of dozens to hundreds of spins bind together and can be excited resonantly by a strong ac magnetic field. The structure of these clusters can by studied via a Fano resonance technique using pump-probe magnetic susceptibility measurements, revealing lifetimes and coherent quantum interference between different excitation channels. In addition, we can tune the dynamics of the quantum degrees of freedom by tuning the strength of the pump ac magnetic field, or by introducing a static transverse field that serves to quantum-mechanically mix spin states. At special values of these two fields, zero-crossings of the Fano asymmetry parameter are observed, which are associated with a dissipationless response at the drive frequency. At these points, certain spin-clusters are minimally coupled with their environment, due to quantum interference between different excitation channels. The lifetimes of these excitations can be measured directly in the time-domain.