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

Unraveling the inhomogeneously broadened absorption spectrum of conjugated polymers by single-molecule light-harvesting action spectroscopy

Journal ArticleThe distribution of chromophores in single polymer chains is revealed by photoluminescence excitation spectroscopy under excitation of the backbone and detection of emission from an end cap. Spectral broadening in excitation exceeds that in emission. An increase in vibronic coupling for shorter (higher energy) chromophores is resolved, leading to intrinsic spectral broadening and making higher energy units more effective donors. The results suggest routes to increasing absorption breadth while minimizing disorder as required for efficient photovoltaics

Simultaneous Raman and fluorescence spectroscopy of single conjugated polymer chains

Journal ArticleSimultaneous surface enhanced Raman scattering (SERS) and fluorescence is demonstrated from single conjugated polymer chains. As resonance enhancement of SERS depends on the spectral overlap of the polymer's absorption and the incident laser, resonance Raman and fluorescence effectively probe the absorbing and emitting part of the polymer, respectively. The optical phonon energies change along the polymer chain, providing a window to spatially track excited state relaxation. Whereas a mean spatial redistribution of the excitation is witnessed by a change in vibronic fingerprint following interchromophoric energy transfer, intrachromophoric exciton self-trapping leaves the vibrations unchanged

Physics and optimization of beta-beams: From low to very high gamma

The physics potential of beta beams is investigated from low to very high gamma values and it is compared to superbeams and neutrino factories. The gamma factor and the baseline are treated as continuous variables in the optimization of the beta beam, while a fixed mass water Cherenkov detector or a totally active scintillator detector is assumed. We include in our discussion also the gamma dependence of the number of ion decays per year. For low gamma, we find that a beta beam could be a very interesting alternative to a superbeam upgrade, especially if it is operated at the second oscillation maximum to reduce correlations and degeneracies. For high gamma, we find that a beta beam could have a potential similar to a neutrino factory. In all cases, the sensitivity of the beta beams to CP violation is very impressive if similar neutrino and anti-neutrino event rates can be achieved.Comment: 34 pages, 16 figures, Fig. 2 modified, discussion improved, refs. added, version to appear in PR

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

Vortices in dipolar Bose-Einstein condensates

Quantized vortices are the hallmark of superfluidity, and are often sought out as the first observable feature in new superfluid systems. Following the recent experimental observation of vortices in Bose-Einstein condensates comprised of atoms with inherent long-range dipole-dipole interactions [Nat. Phys. 18, 1453-1458 (2022)], we thoroughly investigate vortex properties in the three-dimensional dominantly dipolar regime, where beyond-mean-field effects are crucial for stability, and investigate the interplay between trap geometry and magnetic field tilt angle.Comment: 15 pages, 6 figure