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 … » More …

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 … » More …

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 … » More …

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. … » More …

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 … » More …

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

Jeff Steinhauer: Observation of quantum Hawking radiation and its entanglement in an analogue black hole

We observe spontaneous Hawking radiation, stimulated by quantum vacuum fluctuations, emanating from an analogue black hole in an atomic Bose–Einstein condensate. Correlations are observed between the Hawking particles outside the black hole and the partner particles inside. These correlations indicate an approximately thermal distribution of Hawking radiation. We find that the high-energy pairs are entangled, while the low-energy pairs are not, within the reasonable assumption that excitations with different frequencies are not correlated. … » More …

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 … » More …

For Thursday 26 April 2018 we will discuss:

X. Cui: Spin-orbit coupling induced quantum droplet in ultracold Bose-Fermi mixtures [arXiv:1804.04552]

Quantum droplets have intrigued much attention recently in view of their successful observations in the ultracold homonuclear atoms. In this work, we demonstrate a new mechanism for the formation of quantum droplet in heteronuclear atomic systems, i.e., by applying the synthetic spin-orbit coupling(SOC). Take the Bose-Fermi mixture for example, we show that by imposing a Rashba SOC between the spin states of fermions, the greatly suppressed Fermi pressure can enable the formation of Bose-Fermi droplets even for very weak boson-fermion attractions, which are … » More …

For Thursday 19 April 2018 we will discuss:

M. Wenzel et al: Anisotropic Critical Velocity of a Dipolar Superfluid [arXiv:1804.04552]

We present transport measurements on a dipolar superfluid using a Bose-Einstein condensate of 162^Dy with strong magnetic dipole-dipole interactions. By moving an attractive laser beam through the condensate we observe an anisotropic critical velocity for the breakdown of dissipationless flow, which, in the spirit of the Landau criterion, can directly be connected to the anisotropy of the underlying dipolar excitation spectrum. In addition, the heating rate above this critical velocity reflects the same anisotropy. Our observations are in excellent agreement with simulations based on … » More …

For Thursday 5 April 2018 we will discuss the following article:

Senne Van Loon, Wout Van Alphen, Jacques Tempere, and Hadrien Kurkjian: Transition from supersonic to subsonic dispersive shock waves in superfluid Fermi gases

We study the propagation of shock waves in superfluid Fermi gases in the BEC-BCS crossover. Unlike in other superfluid systems, where shock waves have already been studied and observed, Fermi gases can exhibit a subsonic dispersion relation for which the shock wave pattern appears at the tail of the wavefront. We show that this property can be used to distinguish between a subsonic and a supersonic dispersion relation at … » More …