18 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
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
Preparation and spectroscopy of a metastable Mott insulator state with attractive interactions
We prepare and study a metastable attractive Mott insulator state formed with
bosonic atoms in a three-dimensional optical lattice. Starting from a Mott
insulator with Cs atoms at weak repulsive interactions, we use a magnetic
Feshbach resonance to tune the interactions to large attractive values and
produce a metastable state pinned by attractive interactions with a lifetime on
the order of 10 seconds. We probe the (de-)excitation spectrum via lattice
modulation spectroscopy, measuring the interaction dependence of two- and
three-body bound state energies. As a result of increased on-site three-body
loss we observe resonance broadening and suppression of tunneling processes
that produce three-body occupation.Comment: 7 pages, 6 figure
Developing more detailed taxonomies of tobacco industry political activity in low-income and middle-income countries:Qualitative evidence from eight countries
Demonstration of the temporal matter-wave Talbot effect for trapped matter waves
We demonstrate the temporal Talbot effect for trapped matter waves using ultracold atoms in an optical lattice. We investigate the phase evolution of an array of essentially non-interacting matter waves and observe matter-wave collapse and revival in the form of a Talbot interference pattern. By using long expansion times, we image momentum space with sub-recoil resolution, allowing us to observe fractional Talbot fringes up to tenth order
Three-body correlation functions and recombination rates for bosons in three and one dimensions
We investigate local three-body correlations for bosonic particles in three
and one dimensions as a function of the interaction strength. The three-body
correlation function g(3) is determined by measuring the three-body
recombination rate in an ultracold gas of Cs atoms. In three dimensions, we
measure the dependence of g(3) on the gas parameter in a BEC, finding good
agreement with the theoretical prediction accounting for beyond-mean-field
effects. In one dimension, we observe a reduction of g(3) by several orders of
magnitude upon increasing interactions from the weakly interacting BEC to the
strongly interacting Tonks-Girardeau regime, in good agreement with predictions
from the Lieb-Liniger model for all strengths of interaction.Comment: 5 figure
Fabrication and characterization of a multimodal 3D printed mouse phantom for ionoacoustic quality assurance in image-guided pre-clinical proton radiation research
Objective. Image guidance and precise irradiation are fundamental to ensure the reliability of small animal oncology studies. Accurate positioning of the animal and the in-beam monitoring of the delivered radio-therapeutic treatment necessitate several imaging modalities. In the particular context of proton therapy with a pulsed beam, information on the delivered dose can be retrieved by monitoring the thermoacoustic waves resulting from the brief and local energy deposition induced by a proton beam (ionoacoustics). The objective of this work was to fabricate a multimodal phantom (x-ray, proton, ultrasound, and ionoacoustics) allowing for sufficient imaging contrast for all the modalities. Approach. The phantom anatomical parts were extracted from mouse computed tomography scans and printed using polylactic acid (organs) and a granite/polylactic acid composite (skeleton). The anatomical pieces were encapsulated in silicone rubber to ensure long term stability. The phantom was imaged using x-ray cone-beam computed tomography, proton radiography, ultrasound imaging, and monitoring of a 20 MeV pulsed proton beam using ionoacoustics. Main results. The anatomical parts could be visualized in all the imaging modalities validating the phantom capability to be used for multimodal imaging. Ultrasound images were simulated from the x-ray cone-beam computed tomography and co-registered with ultrasound images obtained before the phantom irradiation and low-resolution ultrasound images of the mouse phantom in the irradiation position, co-registered with ionoacoustic measurements. The latter confirmed the irradiation of a tumor surrogate for which the reconstructed range was found to be in reasonable agreement with the expectation. Significance. This study reports on a realistic small animal phantom which can be used to investigate ionoacoustic range (or dose) verification together with ultrasound, x-ray, and proton imaging. The co-registration between ionoacoustic reconstructions of the impinging proton beam and x-ray imaging is assessed for the first time in a pre-clinical scenario