• Event: Workshop "Bosonic Josephson junctions and tunnel-coupled systems" (2009)

• Event: Workshop "Bosonic Josephson junctions and tunnel-coupled systems" (2009)

"We propose a new approach to dynamic decoherence control of many-body systems, focusing on finite-temperature Bose-Einstein Condensates (BEC) in a double-well potential. Due to the many-body interactions the standard “echo” control method becomes less effective. The proposed approach takes advantage of the interaction-induced change of the spectrum, to obtain the optimal rate of pi-flips of the relative phase between maximally distinguishable collective states. This method is particularly useful for probing and diagnosing the many-body decoherence dynamics."

• Event: Workshop "Bosonic Josephson junctions and tunnel-coupled systems" (2009)

Using a Luttinger-liquid approach we study the quantum fluctuations of a Bose-Josephson junction, consisting of a Bose gas confined to a quasi one-dimensional ring trap which contains a localized repulsive potential barrier. For an infinite barrier we study the one-particle and two-particle static correlation functions. For the one-body density-matrix we obtain different power-law decays depending on the location of the probe points with respect to the position of the barrier. This quasi-long range order can be experimentally probed in principle using an interference measurement.
The corresponding momentum distribution at small momenta is also shown to be affected by the presence of the barrier and to display the universal power-law behavior expected for an interacting 1D fluid. We also evaluate the particle density profile, and by comparing with the exact results in the Tonks-Girardeau limit we fix the nonuniversal parameters of the Luttinger-liquid theory. Once the parameters are determined from one-body properties, we evaluate the density-density correlation function, finding a remarkable agreement between the Luttinger liquid predictions and the exact result in the Tonks-Girardeau limit, even at the length scale of the Friedel-like oscillations which characterize the behavior of the density-density correlation function at intermediate distance. Finally, for a large but finite barrier we use the one-body correlation function to estimate the effect of quantum fluctuations on the renormalization of the barrier height, finding a reduction of the effective Josephson coupling energy, which depends on the length of the ring and on the interaction strength.

• Event: Workshop "Bosonic Josephson junctions and tunnel-coupled systems" (2009)

We present the results of our numerical simulations of the transient (time-dependent) and steady-state distribution of the relative phase of two coherently-split 1D atomic quasicondensates. We demonstrate the way to determine both the temperature and tunnel-coupling energy of two condensates from measurements of the relative phase autocorrelation function and the phase-contrast distribution in the steady-state limit. The evolution of the relative phase from its initial to final distribution and the underlying dephasing mechanism are discussed with regard to the numerically obtained scaling properties of the typical time of the subexponential decay of the phase coherence.

• Event: Workshop "Bosonic Josephson junctions and tunnel-coupled systems" (2009)

• Event: Workshop "Bosonic Josephson junctions and tunnel-coupled systems" (2009)

One-dimensional (1D) strongly interacting quantum systems show surprising many-body effects as quantum fluctuations and correlations are enhanced by the confinement. I report on the realization of a highly-correlated, excited many-body state with strong attractive interactions. This novel state of matter in 1D geometry is known as the super-Tonks-Girardeau gas (sTG) and was predicted in [1]. Counter-intuitively, although bosons strongly attract each other in this phase, they behave similar to repulsively interacting fermions, showing an effective long range interaction.
We load a Bose-Einstein condensate of cesium atoms into an array of tube-like 1D traps generated by a 2D optical lattice, and control the interaction strength by means of magnetic Feshbach resonances. When the 3D scattering length is increased towards and beyond the length scale set by the tight transversal confinement, a confinement-induced resonance [2] is observed, that allows us to tune the effective 1D-interaction parameter to large positive and large negative values. We realize the crossover all the way from a non-interacting gas, via the 1D mean-field and Tonks-Girardeau regime, to the sTG gas. Despite the fact that the interaction is strongly attractive, we find the sTG gas to be surprisingly stable.

• Event: Workshop "Bosonic Josephson junctions and tunnel-coupled systems" (2009)

The mystery of the apparent relative phase between independent condensates [1] is explained by the bosonic Quantum de Finetti Theorem [2].
[1] Observation of interference between two Bose condensates, Science 275: 637 - 641 (1997) [2] Locally normal symmetric states and an analogue of de Finetti’s theorem, Z. fuer Wahrscheinlichkeit und verw. Geb. 33: 343 – 351 (1976)

• Event: Workshop "Bosonic Josephson junctions and tunnel-coupled systems" (2009)

We present a theory of measurement-induced interference for weakly interacting Bose-Einstein condensed (BEC) gases.
We show that the many-body state resulting from evolution from an initial fragmented (Fock) state can be approximated as a superposition of Gross-Pitaevskii (GP) states; the measurement breaks the initial U(1) phase symmetry, producing a distribution pattern corresponding to only one of the GP solutions. Analytically solvable models, such as two-mode on-chip adiabatic recombination and soliton generation in quasi one-dimensional condensates, will be briefly commented upon.

• Event: Workshop "Bosonic Josephson junctions and tunnel-coupled systems" (2009)

We study a system composed of one electron and two doubly charged ions which are held in a Penning trap. There exist electronically highly excited states in which the electron is delocalized among the two ions forming a giant molecule of several micrometer size. At energies close to the top of the Coulomb barrier these molecular states can be regarded as superpositions of Rydberg states of individual ions. We illuminate the possibility for observing coherent charge transfer between the ions caused by laser induced tunneling between the two Coulomb wells.

• Event: Workshop "Bosonic Josephson junctions and tunnel-coupled systems" (2009)

• Event: Workshop "Bosonic Josephson junctions and tunnel-coupled systems" (2009)

• Event: Workshop "Bosonic Josephson junctions and tunnel-coupled systems" (2009)

We implement a double-well on an atom chip that combines compactness, fast cycle times, and flexible trap geometries. While we currently use only one double-well, our two-layer chip design creates smooth static magnetic multi-well 3D potentials in linear and topologically connected geometries. Atoms are detected by absorption imaging, with an equivalent noise of 1 atom RMS per pixel. Our chip and imaging system are compatible with small and micro BECs ranging from tens to thousands of 87Rb atoms.
We directly measure the atom number statistics of a BEC in double-well and its dependence on the splitting dynamics, atom loss and atom number.
We report -3.5dB of number squeezing. We also investigated number squeezing dependence with temperature and the transition to thermal gases.

• Event: Workshop "Bosonic Josephson junctions and tunnel-coupled systems" (2009)

I will briefly review the physics of antiferromagnetic spinor condensates beyond mean field and its analogies with a three-well system. In the second part of the talk I will present our approach to adiabatically engineer correlated states in such systems and how we plan to implement it experimentally.

• Event: Workshop "Bosonic Josephson junctions and tunnel-coupled systems" (2009)

Entanglement-based technologies, such as quantum information processing, quantum simulations, and quantum-enhanced metrology, have the potential to revolutionize our way of computing and measuring and help to clarify the puzzling concept of entanglement itself. Ultracold atoms on atom chips are an attractive system for their implementation, as they provide control over quantum systems in a compact, robust, and scalable setup. An enabling technology in this system is a potential depending on the internal atomic state.
Coherent dynamics in such a potential combined with collisional interactions allows entanglement generation both for individual atoms and ensembles. Here we report experiments in which we demonstrate coherent dynamics of Bose-condensed atoms in such a potential, generated in a novel way with microwave near-fields on an atom chip.
We entangle atomic internal and motional states in a controlled and reversible way, realizing a trapped-atom interferometer with internal-state labeling. Furthermore, our system provides control over collisions in mesoscopic condensates with well-defined atom number, paving the way for on-chip generation of many-particle entanglement and quantum-enhanced metrology with spin-squeezed states.

• Event: Workshop "Bosonic Josephson junctions and tunnel-coupled systems" (2009)

• Event: Workshop "Bosonic Josephson junctions and tunnel-coupled systems" (2009)