Dynamical control of matter-wave tunneling in periodic potentials

We report on measurements of dynamical suppression of inter-well tunneling of a Bose-Einstein condensate (BEC) in a strongly driven optical lattice. The strong driving is a sinusoidal shaking of the lattice corresponding to a time-varying linear potential, and the tunneling is measured by letting the BEC freely expand in the lattice. The measured tunneling rate is reduced and, for certain values of the shaking parameter, completely suppressed. Our results are in excellent agreement with theoretical predictions. Furthermore, we have verified that in general the strong shaking does not destroy the phase coherence of the BEC, opening up the possibility of realizing quantum phase transitions by using the shaking strength as the control parameter.Comment: 5 pages, 3 figure

Collapse and revival in inter-band oscillations of a two-band Bose-Hubbard model

We study the effect of a many-body interaction on inter-band oscillations in a two-band Bose-Hubbard model with external Stark force. Weak and strong inter-band oscillations are observed, where the latter arise from a resonant coupling of the bands. These oscillations collapse and revive due to a weak two-body interaction between the atoms. Effective models for oscillations in and out of resonance are introduced that provide predictions for the system's behaviour, particularly for the time-scales for the collapse and revival of the resonant inter-band oscillations.Comment: 10 pages, 5 figure

Resonantly enhanced tunneling of Bose-Einstein condensates in periodic potentials

We report on measurements of resonantly enhanced tunneling of Bose-Einstein condensates loaded into an optical lattice. By controlling the initial conditions of our system we were able to observe resonant tunneling in the ground and the first two excited states of the lattice wells. We also investigated the effect of the intrinsic nonlinearity of the condensate on the tunneling resonances.Comment: accepted for publication in Phys. Rev. Letter

Observation of St\"{u}ckelberg oscillations in accelerated optical lattices

We report the experimental observation of St\"{u}ckelberg oscillations of matter waves in optical lattices. Extending previous work on Landau-Zener tunneling of Bose-Einstein condensates in optical lattices, we study the effects of the accumulated phase between two successive crossings of the Brillouin zone edge. Our results agree well with a simple model for multiple Landau-Zener tunneling events taking into account the band structure of the optical lattice.Comment: 4 pages, 4 figure

Observation of photon-assisted tunneling in optical lattices

We have observed tunneling suppression and photon-assisted tunneling of Bose-Einstein condensates in an optical lattice subjected to a constant force plus a sinusoidal shaking. For a sufficiently large constant force, the ground energy levels of the lattice are shifted out of resonance and tunneling is suppressed; when the shaking is switched on, the levels are coupled by low-frequency photons and tunneling resumes. Our results agree well with theoretical predictions and demonstrate the usefulness of optical lattices for studying solid-state phenomena.Comment: 5 pages, 3 figure

Time-resolved measurement of Landau--Zener tunneling in different bases

A comprehensive study of the tunneling dynamics of a Bose--Einstein condensate in a tilted periodic potential is presented. We report numerical and experimental results on time-resolved measurements of the Landau--Zener tunneling of ultracold atoms introduced by the tilt, which experimentally is realized by accelerating the lattice. The use of different protocols enables us to access the tunneling probability, numerically as well as experimentally, in two different bases, namely, the adiabatic basis and the diabatic basis. The adiabatic basis corresponds to the eigenstates of the lattice, and the diabatic one to the free-particle momentum eigenstates. Our numerical and experimental results are compared with existing two-state Landau--Zener models

Feshbach spectroscopy and dual-species Bose-Einstein condensation of 23Na−^{23}\mathrm{Na}-39K^{39}\mathrm{K} mixtures

We present measurements of interspecies Feshbach resonances and subsequent creation of dual-species Bose-Einstein condensates of $^{23}\mathrm{Na}$ and $^{39}\mathrm{K}$. We prepare both optically trapped ensembles in the spin state $\left|f = 1,m_{f}=-1\right\rangle$ and perform atom loss spectroscopy in a magnetic field range from 0 to $700 \, \mathrm{G}$. The observed features include several s-wave poles and a zero crossing of the interspecies scattering length as well as inelastic two-body contributions in the $\mathcal{M} = m_{\mathrm{Na}}+m_{\mathrm{K}} = -2$ submanifold. We identify and discuss the suitability of different magnetic field regions for the purposes of sympathetic cooling of \K and achieving dual-species degeneracy. Two condensates are created simultaneously by evaporation at a magnetic field of about $150 \, \mathrm{G}$, which provides sizable intra- and interspecies scattering rates needed for fast thermalization. The impact of the differential gravitational sag on the miscibility criterion for the mixture is discussed. Our results serve as a promising starting point for the magnetoassociation into quantum degenerate $^{23}\mathrm{Na}^{39}\mathrm{K}$ Feshbach molecules.Comment: 9 pages, 7 figure

Versatile electric fields for the manipulation of ultracold NaK molecules

In this paper, we present an electrode geometry for the manipulation of ultracold, rovibrational ground state NaK molecules. The electrode system allows to induce a dipole moment in trapped diatomic NaK molecules with a magnitude up to 68% of their internal dipole moment along any direction in a given two-dimensional plane. The strength, the sign and the direction of the induced dipole moment is therefore fully tunable. The maximal relative variation of the electric field over the trapping volume is below 10-6. At the desired electric field value of 10 kV cm-1 this corresponds to a deviation of 0.01 V cm-1. Furthermore, the possibility to create strong electric field gradients provides the opportunity to address molecules in single layers of an optical lattice. The electrode structure is made of transparent indium tin oxide and combines large optical access for sophisticated optical dipole traps and optical lattice configurations with the possibility to create versatile electric field configurations.Centre for Quantum Engineering and Space-Time Research QUESTERC Starting Grant POLARDFG/GRK/1729DFG/GRK/199