CMT seminar: Quantum Simulation of Many-Body Spin Systems: From Ground States to Dynamics
Thursday, April 24, 2014 – 1:30pm – 3:00pm
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