Freezing a Quantum Magnet by Repeated Quantum Interference: An Experimental Realization

We experimentally demonstrate the phenomenon of dynamical many-body freezing in a periodically driven Ising chain. Theoretically [Phys. Rev. B 82, 172402 (2010)], for certain values of the drive parameters all fundamental degrees of freedom contributing to the response dynamics freeze for all time and for arbitrary initial states. Also, since the condition of freezing involves only the drive parameters and not on the quantization of the momentum (i.e., the system-size), our simulation with a small (3-spin) chain captures all salient features of the freezing phenomenon predicted for the infinite chain. Using optimal control techniques, we realize high-fidelity cosine modulated drive, and observe non-monotonic freezing of magnetization at specific frequencies of modulation. Time-evolution of the excitations in momentum space has been tracked directly through magnetization measurements.