347 research outputs found
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
Static magnetic proximity effect in Pt/NiFe 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/NiFe, Pt/NiFe (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 and absorption
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
In situ observation of chemistry in Rydberg molecules within a coherent solvent
We often infer the state of systems in nature indirectly, for example in high
energy physics by recording the tracks particles leave behind in an ambient
medium. We adapt this principle to energies 9 orders of magnitude smaller, to
classify the final state of exotic molecules after internal conversion of their
electronic state, through their interaction with an ambient quantum fluid, a
Bose-Einstein condensate. The BEC is the ground-state of a million bosonic
atoms near zero temperature, and a single embedded ultra-long range Rydberg
molecule can coherently excite waves in this fluid, which carry tell-tale
signatures of its dynamics. Bond lengths exceeding a micrometer allow us to
observe the molecular fingerprint on the BEC in situ, via optical microscopy.
Interpreting images in comparison with simulations shows that the molecular
electronic state rapidly converts from the initially excited S- and D-orbitals
to a much more complex molecular state (called "trilobite''), marked by a
maximally localized electron. This internal conversion liberates energy, such
that one expects final state particles to move rapidly through the medium,
which is however ruled out by comparing experiment and simulations. The
molecule thus must strongly decelerate in the medium, for which we propose a
plausible mechanism. Our experiment demonstrates a coherent medium that
facilitates and records an electronic state change of embedded exotic molecules
in ultra-cold chemistry, with sufficient sensitivity to constrain velocities of
final state particles.Comment: 11 pages and 11 figure
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