Sep 2016

Aug 29-Sep 2 Max, Sep 5-Sep 9 Biao Huang, Sep 12-Sep 16 Haiyuan Zou, Sep 19-Sep 23 Ahmet Kel, Sep 26-Sep 30 Zehan Li

Sep 16
 arXiv:1609.04800 [pdf, other]
Synthetic dimensions and spin-orbit coupling with an optical clock transition
L. F. Livi, G. Cappellini, M. Diem, L. Franchi, C. Clivati, M. Frittelli, F. Levi, D. Calonico, J. Catani, M. Inguscio, L. Fallani
Subjects: Quantum Gases (cond-mat.quant-gas); Atomic Physics (physics.atom-ph); Quantum Physics (quant-ph)

We demonstrate a novel way of synthesizing spin-orbit interactions in ultracold quantum gases, based on a single-photon optical clock transition coupling two long-lived electronic states of two-electron 173Yb atoms. By mapping the electronic states onto effective sites along a synthetic "electronic" dimension, we have engineered synthetic fermionic ladders with tunable magnetic fluxes. We have detected the spin-orbit coupling with fiber-link-enhanced clock spectroscopy and directly measured the emergence of chiral edge currents, probing them as a function of the magnetic field flux. These results open new directions for the investigation of topological states of matter with ultracold atomic gases.
Sep 15
 arXiv:1609.04046 [pdf, other]
Quantum heat waves in a one-dimensional condensate
Kartiek Agarwal, Emanuele G. Dalla Torre, Jörg Schmiedmayer, Eugene Demler
Comments: 12+epsilon pages + Refs., 8 figures
Subjects: Quantum Gases (cond-mat.quant-gas)
We study the dynamics of phase relaxation between a pair of one-dimensional condensates created by a bi-directional, supersonic `unzipping' of a finite single condensate. We find that the system fractures into different \emph{extensive} chunks of space-time, within which correlations appear thermal but correspond to different effective temperatures. Coherences between different eigen-modes are crucial for understanding the development of such thermal correlations; at no point in time can our system be described by a generalized Gibbs' ensemble despite nearly always appearing locally thermal. We rationalize a picture of propagating fronts of hot and cold sound waves, populated at effective, relativistically red- and blue-shifted temperatures to intuitively explain our findings. The disparity between these hot and cold temperatures vanishes for the case of instantaneous splitting but diverges in the limit where the splitting velocity approaches the speed of sound; in this limit, a sonic boom occurs wherein the system is excited only along an infinitely narrow, and infinitely hot beam. We expect our findings to apply generally to the study of superluminal perturbations in systems with emergent Lorentz symmetry.

Sep 14
arXiv:1609.03563 [pdf, other]
Topological Magnon Insulator in the Frustrated Kagomé-Lattice Antiferromagnets
S. A. Owerre
Comments: 7 pages, 7 figures

Subjects: Strongly Correlated Electrons (cond-mat.str-el)
Insulating antiferromagnets on the Kagom\'e lattice are frustrated systems in which highly-correlated spins keep fluctuating down to very low temperatures. In these systems the Dzyaloshinskii-Moriya (DM) interaction does not provide spin-orbit (SO) coupling as opposed to ferromagnets. Hence, frustrated Kagom\'e antiferromagnets can be deemed topologically trivial. Many frustrated magnets, however, show evidence of magnetic ordering in the presence of a magnetic field applied perpendicular to the Kagom\'e plane. In most cases the magnetic field induces a non-coplanar spin texture with nonzero spin scalar chirality. This type of magnetic ordering has been verified experimentally in the ideal frustrated Kagom\'e antiferromagnet, iron jarosite KFe3(OH)6(SO4)2. Nevertheless, the topological nature of this non-coplanar spin texture has not been scrutinized both theoretically and experimentally. It is shown that frustrated Kagom\'e antiferromagnetic materials with field-induced non-collinear spin configurations are candidates for topological magnon insulators.


Sep 13

arXiv:1609.03113 [pdf, other]
Ultrafast coherent control of spinor Bose-Einstein condensates using stimulated Raman adiabatic passage
Andreas Thomasen, Tetsuya Mukai, Tim Byrnes
Comments: 15 pages, 5 figures
Subjects: Quantum Gases (cond-mat.quant-gas); Quantum Physics (quant-ph)

We propose the use of stimulated Raman adiabatic passage (STIRAP) to offer a fast high fidelity method of performing SU(2) rotations on spinor Bose Einstein condensates (BEC). Past demonstrations of BEC optical control suffer from difficulties arising from collective enhancement of spontaneous emission and inefficient two-photon transitions originating from selection rules. We present here a novel scheme which allows for arbitrary coherent rotations of two-component BECs while overcoming these issues. Numerical tests of the method show that for BECs of \ce{^{87}Rb} with up to 104 atoms and gate times of $\SI{1}{\micro\second}$, decoherence due to spontaneous emission can be suppressed to negligible values.

Sep 12

arXiv:1609.02807 [pdf, other]
Cosine Edge Mode in a Periodically Driven Quantum System
Indubala I. Satija, Erhai Zhao
Subjects: Quantum Gases (cond-mat.quant-gas)

Time-periodic (Floquet) topological phases of matter exhibit bulk-edge relationships that are more complex than static topological insulators and superconductors. Finding the edge modes unique to driven systems usually requires numerics. Here we present a minimal two-band model of Floquet topological insulators and semimetals in two dimensions where all the bulk and edge properties can be obtained analytically. It is based on the extended Harper model of quantum Hall effect at flux one half. We show that periodical driving gives rise to a series of phases characterized by a pair of integers. The model has a most striking feature: the spectrum of the edge modes is always given by a single cosine function, ω(ky)∝cosky where ky is the wave number along the edge, as if it is freely dispersing and completely decoupled from the bulk. The cosine mode is robust against the change in driving parameters and persists even to semi-metallic phases with Dirac points. The localization length of the cosine mode is found to contain an integer and in this sense quantized.



Sep 08

Dynamical Gauge Effects and Holographic Scaling of Non-Equilibrium Motion in a Disordered and Dissipative Atomic Gas
Jianshi Zhao, Craig Price, Qi Liu, Louis Jacome, Nathan Gemelke
(Submitted on 7 Sep 2016)

We present a table-top realization of a non-equilibrium quantum system described by a dynamical gauge field propagating on an effectively curved space and time manifold. The system is formed by neutral atoms interacting with both a conservative disordered optical field and a dissipative pumping field. In the presence of a sufficiently dark state, we demonstrate non-equilibrium behavior reminiscent of the information paradox in black hole physics. At a well-defined transition point, the analog of gauge-boson mass is seen to vanish, inducing scale-invariant behavior as a Higgs-like mechanism is removed. The subsequent scaling behavior can be understood using the holographic principle with a tunable analog of the Planck length derived from the scaling of disorder. These effects suggest a range of new phenomena in weakly dissipative quantum systems, including the presence of analog forms of emergent gravitation.


Sep 06
arXiv:1609.01271
Emergence of a Turbulent Cascade in a Quantum Gas
Nir Navon, Alexander L. Gaunt, Robert P. Smith, Zoran Hadzibabic
(Submitted on 5 Sep 2016)

In the modern understanding of turbulence, a central concept is the existence of cascades of excitations from large to small lengthscales, or vice-versa. This concept was introduced in 1941 by Kolmogorov and Obukhov, and the phenomenon has since been observed in a variety of systems, including interplanetary plasmas, supernovae, ocean waves, and financial markets. Despite a lot of progress, quantitative understanding of turbulence remains a challenge due to the interplay of many lengthscales that usually thwarts theoretical simulations of realistic experimental conditions. Here we observe the emergence of a turbulent cascade in a weakly interacting homogeneous Bose gas, a quantum fluid that is amenable to a theoretical description on all relevant lengthscales. We prepare a Bose-Einstein condensate (BEC) in an optical box, drive it out of equilibrium with an oscillating force that pumps energy into the system at the largest lengthscale, study the BEC's nonlinear response to the periodic drive, and observe a gradual development of a cascade characterised by an isotropic power-law distribution in momentum space. We numerically model our experiments using the Gross-Pitaevskii equation (GPE) and find excellent agreement with the measurements. Our experiments establish the uniform Bose gas as a promising new platform for investigating many aspects of turbulence, including the interplay of vortex and wave turbulence and the relative importance of quantum and classical effects.