|Nov. 18th (Fri) 10:30 a.m.
|Dr. 최 순 원, Havard University
Non-equilibrium many-body spin dynamics in diamond
Dr. 최 순 원, Havard University
Nov. 18th (Fri) 10:30 a.m., #5318(5th fl.)
In this talk, we will discuss two recent developments in non-equilibrium quantum dynamics of strongly interacting many-body systems: I. critically slow thermalization in a disordered dipolar spin ensemble  and II. the observation of discrete time crystalline order . Both of these experiments were enabled by a high density ensemble of nitrogen-vacancy (NV) color centers in diamond . As a mixture of theory and experiments, the talk will be self-contained and pedagogical, reviewing some of basic concepts in many-body localization, Floquet time-crystal, spin properties of NV centers and experimental techniques to manipulate and engineer the dynamics.
Statistical mechanics underlies our understanding of macroscopic quantum systems. It is based on the assumption that out-of-equilibrium systems rapidly approach their equilibrium states, forgetting any information about their microscopic initial conditions. This fundamental paradigm is challenged by disordered systems, in which a slowdown or even absence of thermalization is expected. By controlling the spin states of the ~10^6 NV centers, we observe slow, sub-exponential thermalization consistent with power laws that exhibit disorder-dependent exponents; this behavior is modified at late times owing to many-body interactions. These observations are quantitatively explained by a resonance counting theory that incorporates the effects of both disorder and interactions
The interplay of periodic driving, disorder, and strong interactions has recently been predicted to result in exotic ``time-crystalline'' phases, which spontaneously break the discrete time-translation symmetry of the underlying drive. We report the experimental observation of such discrete time-crystalline order and the observation of long-lived temporal correlations at integer multiples of the fundamental driving period. We experimentally identify the phase boundary and find that the temporal order is protected by strong interactions; this order is remarkably stable against perturbations, even in the presence of slow thermalization. We provide a theoretical description of approximate Floquet eigenstates of the system based on product state ansatz and predict the phase boundary, which is in qualitative agreement with our observations.
 G. Kucsko et al, arXiv:1609.08216
 S. Choi et al, arXiv:1610.08057
 J. Choi et al, arXiv:1608.05471
Contact: Eun-Gook Moon, Physics Dept., (email@example.com)