Thermalization is a ubiquitous process of statistical physics, in which a physical system reaches an equilibrium state that is defined by a few global properties such as temperature. Even in isolated quantum many-body systems, limited to reversible dynamics, thermalization typically prevails1. However, in these systems, there is another possibility: many-body localization (MBL) can result in preservation of a non-thermal state2,3. While disorder has long been considered an essential ingredient for this phenomenon, recent theoretical work has suggested that a quantum many-body system with a spatially increasing field{\textemdash}but no disorder{\textemdash}can also exhibit MBL4, resulting in {\textquoteleft}Stark MBL{\textquoteright}5. Here we realize Stark MBL in a trapped-ion quantum simulator and demonstrate its key properties: halting of thermalization and slow propagation of correlations. Tailoring the interactions between ionic spins in an effective field gradient, we directly observe their microscopic equilibration for a variety of initial states, and we apply single-site control to measure correlations between separate regions of the spin chain. Furthermore, by engineering a varying gradient, we create a disorder-free system with coexisting long-lived thermalized and non-thermal regions. The results demonstrate the unexpected generality of MBL, with implications about the fundamental requirements for thermalization and with potential uses in engineering long-lived non-equilibrium quantum matter.

}, issn = {1476-4687}, doi = {10.1038/s41586-021-03988-0}, url = {https://doi.org/10.1038/s41586-021-03988-0}, author = {Morong, W. and Liu, F. and Becker, P. and Collins, K. S. and Feng, L. and Kyprianidis, A. and Pagano, G. and You, T. and Gorshkov, A. V. and Monroe, C.} } @article { ISI:000550690300003, title = {On-demand indistinguishable single photons from an efficient and pure source based on a Rydberg ensemble}, journal = {Optica}, volume = {7}, number = {7}, year = {2020}, month = {JUL 20}, pages = {813-819}, publisher = {OPTICAL SOC AMER}, type = {Article}, abstract = {Single photons coupled to atomic systems have shown to be a promising platform for developing quantum technologies. Yet a bright on-demand, highly pure, and highly indistinguishable single-photon source compatible with atomic platforms is lacking. In this work, we demonstrate such a source based on a strongly interacting Rydberg system. The large optical nonlinearities in a blockaded Rydberg ensemble convert coherent light into a single collective excitation that can be coherently retrieved as a quantum field. We simultaneously observe a fully single-mode (spectral, temporal, spatial, and polarization) efficiency up to 0.098(2), a detector-background-subtracted g((2))+5.0(1.6) x 10(-4), and indistinguishability of 0.980(7), at an average photon production rate of 1.18(2) x 10(4) s(-1), All of these make this system promising for scalable quantum information applications. Furthermore, we investigate the effects of contaminant Rydberg excitations on the source efficiency and observed single-mode efficiencies up to 0.18(2) for lower photon rates. Finally, recognizing that many quantum information protocols require a single photon in a fully single mode, we introduce metrics that take into account all degrees of freedom to benchmark the performance of on-demand sources. (C) 2020 Optical Society of America under the terms of the OSA Open Access Publishing Agreement}, issn = {2334-2536}, doi = {10.1364/OPTICA.391485}, author = {Ornelas-Huerta, D. P. and Craddock, A. N. and Goldschmidt, E. A. and Hachtel, A. J. and Wang, Y. and Bienias, P. and Gorshkov, A. V. and Rolston, S. L. and Porto, J. V.} } @article { ISI:000443327900004, title = {Optimization of photon storage fidelity in ordered atomic arrays}, journal = {NEW JOURNAL OF PHYSICS}, volume = {20}, year = {2018}, month = {AUG 31}, pages = {083048}, keywords = {atomic ensembles, quantum memory, subradiance, superradiance}, issn = {1367-2630}, doi = {10.1088/1367-2630/aadb74}, author = {Manzoni, M. T. and Moreno-Cardoner, M. and Asenjo-Garcia, A. and Porto, J. V. and Gorshkov, A. V. and Chang, D. E.} } @article {ISI:000430909100001, title = {Out-of-time-order correlators in finite open systems}, journal = {PHYSICAL REVIEW B}, volume = {97}, number = {16}, year = {2018}, month = {APR 26}, pages = {161114}, publisher = {AMER PHYSICAL SOC}, type = {Article}, abstract = {We study out-of-time-order correlators (OTOCs) of the form <(A) over cap (t) (B) over cap (0) (C) over cap (t) (D) over cap (0)> for a quantum system weakly coupled to a dissipative environment. Such an open system may serve as a model of, e. g., a small region in a disordered interacting medium coupled to the rest of this medium considered as an environment. We demonstrate that for a system with discrete energy levels the OTOC saturates exponentially alpha Sigma a(i)e(-t/tau i) + const to a constant value at t -> infinity, in contrast with quantum-chaotic systemswhich exhibit exponential growth of OTOCs. Focusing on the case of a two-level system, we calculate microscopically the decay times tau(i) and the value of the saturation constant. Because some OTOCs are immune to dephasing processes and some are not, such correlators may decay on two sets of parametrically different time scales related to inelastic transitions between the system levels and to pure dephasing processes, respectively. In the case of a classical environment, the evolution of the OTOC can be mapped onto the evolution of the density matrix of two systems coupled to the same dissipative environment.}, \%\%Address = {ONE PHYSICS ELLIPSE, COLLEGE PK, MD 20740-3844 USA}, issn = {2469-9950}, doi = {10.1103/PhysRevB.97.161114}, author = {Syzranov, S. V. and Gorshkov, A. V. and Galitski, V.} }