# CMT seminar: Quantum Simulation of Many-Body Spin Systems: From Ground States to Dynamics

Thursday, April 24, 2014 – 1:30pm – 3:00pm

Regents 351

Phil Richerme

Joint Quantum Institute of the University of Maryland and NIST

For quantum systems of only 30 interacting spins, it can become difficult or impossible to calculate frustrated many-body ground states or dynamical evolution due to the exponential scaling of the Hilbert space with the system size. Trapped-ion quantum simulators map the difficult many-body problem of interest onto a well-controlled and tunable system that can be initialized and read out using standard atomic physics techniques. Phonon-mediated spin-dependent optical dipole forces act globally on a linear chain of up to 18 trapped Yb-171+ ions to generate effective spin-spin interactions, with the form and range of such interactions controlled by laser and trap parameters. State-dependent fluorescence imaging of the ions onto a camera allows for readout of the individual spin states. First, exploiting our precise control over the couplings and external fields, we introduce quantum fluctuations to study a zero-temperature classical spin system where the absence of thermal fluctuations renders the ground states classically inaccessible. I will then describe two experiments that move beyond studies of the ground state. In the first, we have developed a spectroscopic technique to resolve the excited state energy levels of our effective many-body system and verify the experimentally applied Hamiltonian. In the second, we perform a global quench in a long-range interacting system and measure the speed with which correlations propagate through the ion chain, observing velocities that violate Lieb-Robinson type predictions and cannot be explained by any current theory. We expect that such studies of many-body dynamics will be a prime use of quantum simulators as system sizes are extended to 30+ spins, where classical computations become intractable.

Host: Jim Freericks