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21 February 2019: Local spin manipulation of quantized atomic currents

For Thursday 21 February 2019 we will discuss:

  • Martin Lebrat, Samuel Häusler, Philipp Fabritius, Dominik Husmann, Laura Corman, Tilman Esslinger: “Local spin manipulation of quantized atomic currents”

    Spin is a fundamental quantum property of matter, and lifting its degeneracy lies at the heart of subtle transport phenomena and future schemes for quantum information processing. Here, we implement a microscopic spin filter for cold fermionic atoms in a quantum point contact (QPC) which allows us to create fully spin-polarized currents while retaining conductance quantization. Key to our scheme is a near-resonant optical tweezer which induces an effective Zeeman shift inside the QPC while its local character limits dissipation. We measure global effects of non-Hermitian evolution and interactions on the scale of the Fermi wavelength. Our work paves the way to studying hybrid mesoscopic structures combining spin-splitting and superfluidity far from equilibrium.

31 January 2019: Transient supersolid properties in an array of dipolar quantum droplets

For Thursday 31 January 2019 we will discuss:

  • Fabian Böttcher, Jan-Niklas Schmidt, Matthias Wenzel, Jens Hertkorn, Mingyang Guo, Tim Langen, Tilman Pfau: Transient supersolid properties in an array of dipolar quantum droplets

    We study theoretically and experimentally the emergence of supersolid properties in a dipolar Bose-Einstein condensate. The theory reveals a ground state phase diagram with three distinct regimes – a regular Bose-Einstein condensate, incoherent and coherent arrays of quantum droplets. In the latter the droplets are connected by a finite superfluid density, which leads – in addition to the periodic density modulation – to a robust phase coherence throughout the whole system. We further theoretically demonstrate that we are able to dynamically approach the ground state in our experiment and that its lifetime is only limited by three-body losses. Experimentally we probe and confirm the signatures of the phase diagram by observing the in-situ density modulation as well as the phase coherence using matter wave interference.

24 January 2019: Rotating Atomic Quantum Gases with Light-Induced Azimuthal Gauge Potentials and the Observation of the Hess-Fairbank Effect

For Thursday 24 January 2019 we will discuss:

    P.-K. Chen, L.-R. Liu, M.-J. Tsai, N.-C. Chiu, Y. Kawaguchi, S.-K. Yip, M.-S. Chang, and Y.-J. Lin
    Phys. Rev. Lett. 121, 250401 : Rotating Atomic Quantum Gases with Light-Induced Azimuthal Gauge Potentials and the Observation of the Hess-Fairbank Effect

    We demonstrate synthetic azimuthal gauge potentials for Bose-Einstein condensates from engineering atom-light couplings. The gauge potential is created by adiabatically loading the condensate into the lowest energy Raman-dressed state, achieving a coreless vortex state. The azimuthal gauge potentials act as effective rotations and are tunable by the Raman coupling and detuning. We characterize the spin textures of the dressed states, in agreements with the theory. The lowest energy dressed state is stable with a 4.5-s half-atom-number-fraction lifetime. In addition, we exploit the azimuthal gauge potential to demonstrate the Hess-Fairbank effect, the analogue of Meissner effect in superconductors. The atoms in the absolute ground state has a zero quasiangular momentum and transits into a polar-core vortex when the synthetic magnetic flux is tuned to exceed a critical value. Our demonstration serves as a paradigm to create topological excitations by tailoring atom-light interactions where both types of SO(3) vortices in the |⟨→F⟩|=1 manifold, coreless vortices and polar-core vortices, are created in our experiment. The gauge field in the stationary Hamiltonian opens a path to investigating rotation properties of atomic superfluids under thermal equilibrium.

13 December 2018: Density Waves and Jet Emission Asymmetry in Bose Fireworks

For Thursday 13 December 2018 we will discuss:

  • Han Fu, Lei Feng, Brandon M. Anderson, Logan W. Clark, Jiazhong Hu, Jeffery W. Andrade, Cheng Chin, K. Levin: Density Waves and Jet Emission Asymmetry in Bose Fireworks

    A Bose condensate subject to a periodic modulation of the two-body interactions was recently observed to emit matter-wave jets resembling “fireworks” [Nature 551, 356(2017)]. In this paper, combining experiment with numerical simulation, we demonstrate that these “Bose fireworks” represent a late stage in a complex time evolution of the driven condensate. We identify a “density wave” stage which precedes jet emission and results from interference of matterwaves. The density waves self-organize and self-amplify without the breaking of long range translational symmetry. Importantly, this density wave structure deterministically establishes the template for the subsequent patterns of the emitted jets. Our simulations, in good agreement with experiment, also address the apparent asymmetry in the jet pattern and show it is fully consistent with momentum conservation.

29 November 2018: Rotating sonic black hole from Spin-orbit coupled Bose-Einstein condensate

Continuing from last week, for Thursday 29 November 2018 we will discuss:

  • Inderpreet Kaur and Sankalpa Ghosh: Rotating sonic black hole from Spin-orbit coupled Bose-Einstein condensate

    We show that a sonic analogue of rotating BTZ type of black hole can be realised in a quasi-two-dimensional spin-orbit coupled BEC without any external rotation. The corresponding equation for phase fluctuations in total density mode that describes phonon field in hydrodynamic approximation, is described by a scalar field equation in 2+1 dimension whose space-time metric can be identified with the space-time metric of rotating black hole of BTZ type. By time evolving the condensate in a suitably created laser induced potential, we show that the the moving condensate forms such rotating black hole in an annular region bounded by inner and outer event horizon as well as elliptical ergo surfaces. We discuss the self amplifying density modulations as well as the distribution of supersonic and subsonic zones in such rotating black hole that strongly depends on the spin-orbit coupled anisotropy that can be tested in experiments. We also calculate the density-density correlation in such analogue rotating black hole and the distribution of the analogue Hawking temperature on the event horizon.

Related to last week’s discussion is the following paper where they discuss some of the subtitles of measuring entanglement in the photons emitted by the dumb hole:

15 November 2018: Observation of quantum Hawking radiation and its entanglement in an analogue black hole

Inspired by Bill Unruh’s talk last week, for Thursday 15 November 2018 we will discuss:

9 May 2018: Experimental demonstration of shaken lattice interferometry

For Thursday 9 May 2018 we will discuss:

  • C.A. Weidner, Dana Z. Anderson: Experimental demonstration of shaken lattice interferometry [arXiv:1801.09277]

    We experimentally demonstrate a shaken lattice interferometer. Atoms are trapped in the ground Bloch state of a red-detuned optical lattice. Using a closed-loop optimization protocol based on the dCRAB algorithm, we phase-modulate (shake) the lattice to transform the atom momentum state. In this way, we implement an atom beamsplitter and build five interferometers of varying interrogation times TI. The sensitivity of shaken lattice interferometry is shown to scale as T2I, consistent with simulation [1]. Finally, we show that we can measure the sign of an applied signal and optimize the interferometer in the presence of a bias signal.

    [1] C. A. Weidner, H. Yu, R. Kosloff, and D. Z. Anderson, Phys. Rev. A 95, 043624 (2017).