Floquet engineering of correlated tunneling in the Bose-Hubbard model with ultracold atoms

We report on the experimental implementation of tunable occupation-dependent tunneling in a Bose-Hubbard system of ultracold atoms via time-periodic modulation of the on-site interaction energy. The tunneling rate is inferred from a time-resolved measurement of the lattice site occupation after a quantum quench. We demonstrate coherent control of the tunneling dynamics in the correlated many-body system, including full suppression of tunneling as predicted within the framework of Floquet theory. We find that the tunneling rate explicitly depends on the atom number difference in neighboring lattice sites. Our results may open up ways to realize artificial gauge fields that feature density dependence with ultracold atoms.Comment: 8 pages, 9 figure

Vibrational quenching of weakly bound cold molecular ions immersed in their parent gas

Hybrid ion–atom systems provide an excellent platform for studies of state-resolved quantum chemistry at low temperatures, where quantum effects may be prevalent. Here we study theoretically the process of vibrational relaxation of an initially weakly bound molecular ion due to collisions with the background gas atoms. We show that this inelastic process is governed by the universal long-range part of the interaction potential, which allows for using simplified model potentials applicable to multiple atomic species. The product distribution after the collision can be estimated by making use of the distorted wave Born approximation. We find that the inelastic collisions lead predominantly to small changes in the binding energy of the molecular ion.Deutsche ForschungsgemeinschaftCarl-Zeiss foundationBaden-Württemberg-Stiftun

Static magnetic proximity effect in Pt/Ni1−x_{1-x}Fex_x bilayers investigated by x-ray resonant magnetic reflectivity

We present x-ray resonant magnetic reflectivity (XRMR) as a very sensitive tool to detect proximity induced interface spin polarization in Pt/Fe, Pt/Ni$_{33}$Fe$_{67}$, Pt/Ni$_{81}$Fe$_{19}$ (permalloy), and Pt/Ni bilayers. We demonstrate that a detailed analysis of the reflected x-ray intensity gives insight in the spatial distribution of the spin polarization of a non-magnetic metal across the interface to a ferromagnetic layer. The evaluation of the experimental results with simulations based on optical data from ab initio calculations provides the induced magnetic moment per Pt atom in the spin polarized volume adjacent to the ferromagnet. We find the largest spin polarization in Pt/Fe and a much smaller magnetic proximity effect in Pt/Ni. Additional XRMR experiments with varying photon energy are in good agreement with the theoretical predictions for the energy dependence of the magnetooptic parameters and allow identifying the optical dispersion $\delta$ and absorption $\beta$ across the Pt L3-absorption edge

Observation of many-body long-range tunneling after a quantum quench

Quantum tunneling constitutes one of the most fundamental processes in nature. We observe resonantly-enhanced long-range quantum tunneling in one-dimensional Mott-insulating Hubbard chains that are suddenly quenched into a tilted configuration. Higher-order many-body tunneling processes occur over up to five lattice sites when the tilt per site is tuned to integer fractions of the Mott gap. Starting from a one-atom-per-site Mott state the response of the many-body quantum system is observed as resonances in the number of doubly occupied sites and in the emerging coherence in momentum space. Second- and third-order tunneling shows up in the transient response after the tilt, from which we extract the characteristic scaling in accordance with perturbation theory and numerical simulations.Comment: 22 pages, 7 figure