Dec 2016

Nov 28-Dec 2 Max, Dec 5-Dec 9 Biao Huang, Dec 12-Dec 16 Haiyuan Zou, Dec 19-Dec 23 Ahmet Kel

Dec 16
arXiv:1612.05169 [pdf, ps, other]
Testing universality of Efimov physics across broad and narrow Feshbach resonances
Jacob Johansen, B. J. DeSalvo, Krutik Patel, Cheng Chin
Comments: 4 pages, 4 figures, 1 table main text; 2 pages, 1 figure methods; 1 page, 1 figure, 2 tables supplement
Subjects: Quantum Gases (cond-mat.quant-gas)
Efimov physics is a universal phenomenon arising in quantum three-body systems. For systems with resonant two-body interactions, Efimov predicted an infinite series of three-body bound states with geometric scaling symmetry. These Efimov states were first observed in cold Cs atoms and have since been reported in a variety of atomic systems. While theories predict non-universal behavior for narrow Feshbach resonances, experiments on Efimov resonances are so far consistent with predictions based on universal theories. Here we directly compare the Efimov spectra in a 6Li-133Cs mixture near two Feshbach resonances which are very different in their resonance strengths but otherwise almost identical. Our result shows a clear dependence of the Efimov resonance positions on Feshbach resonance strength and a clear departure from the universal prediction for the narrow Feshbach resonance.



Dec 15

arXiv:1612.04627 [pdf, other]
Measuring entropy and mutual information in the two-dimensional Hubbard model
E. Cocchi, L. A. Miller, J. H. Drewes, C. F. Chan, D. Pertot, F. Brennecke, M. Köhl
Subjects: Quantum Gases (cond-mat.quant-gas)
We measure pressure and entropy of ultracold fermionic atoms in an optical lattice for a range of interaction strengths, temperatures and fillings. Our measurements demonstrate that, for low enough temperatures, entropy-rich regions form locally in the metallic phase which are in contact with a Mott-insulating phase featuring lower entropy. In addition, we also measure the reduced density matrix of a single lattice site, and from the comparison between the local and thermodynamic entropies we determine the mutual information between a single lattice site and the rest of the system. For low lattice fillings, we find the mutual information to be independent of interaction strength, however, for half filling we find that strong interactions suppress the correlations between a single site and the rest of the system.



Dec 13
arXiv:1612.03264 [pdf, other]
Vortex-bright solitons in a spin-orbit coupled spin-1 condensate
Sandeep Gautam, S. K. Adhikari
Subjects: Quantum Gases (cond-mat.quant-gas)
We study the vortex-bright solitons in a quasi-two-dimensional spin-orbit-coupled (SO-coupled) hyperfine spin-1 three-component Bose-Einstein condensate (BEC) using variational method and numerical solution of a mean-field model. The ground state of these vortex-bright solitons is radially symmetric for weak ferromagnetic and polar interactions. For a sufficiently strong ferromagnetic interaction, we observe the emergence of an asymmetric vortex-bright soliton as the ground state. We also numerically investigate stable moving solitons and binary collision between them. The present mean-field model is not Galilean invariant, and we use a Galilean-transformed model for generating the moving solitons. At low velocities, the head-on collision between two {\em in-phase} solitons results either in collapse or fusion of the soliton pair. On the other hand, in head-on collision, the two {\em out-of-phase} solitons strongly repel each other and trace back their trajectories before the actual collision. At low velocities, in a collision with an impact parameter, the {\em out-of-phase} solitons get deflected from their original trajectory like two rigid classical disks. These {\em out-of-phase solitons} behave like classical disks, and their collision dynamics is governed by classical laws of motion. However, at large velocities two SO-coupled spinor solitons, irrespective of phase difference, can pass through each other in a head-on collision like two quantum solitons.



Dec 12
arXiv:1612.03038 [pdf, other]
Universal scaling of unequal-time correlation functions in ultracold Bose gases far from equilibrium
A. Schachner, A. Piñeiro Orioli, J. Berges
Comments: 11 pages, 8 figures
Subjects: Quantum Gases (cond-mat.quant-gas); Statistical Mechanics (cond-mat.stat-mech); High Energy Physics - Phenomenology (hep-ph)


We explore the far-from-equilibrium dynamics of Bose gases in a universal regime associated to nonthermal fixed points. While previous investigations concentrated on scaling functions and exponents describing equal-time correlations, we compute the additional scaling functions and dynamic exponent z characterizing the frequency dependence or dispersion from unequal-time correlations. This allows us to compare the characteristic condensation and correlation times from a finite-size scaling analysis depending on the system's volume.


Dec 08 Thursday
arXiv:1612.02434 [pdf, other]
Scrambling and thermalization in a diffusive quantum many-body system
A. Bohrdt, C. B. Mendl, M. Endres, M. Knap
Comments: 8+3 pages, 8+3 figures
Subjects: Quantum Gases (cond-mat.quant-gas); Statistical Mechanics (cond-mat.stat-mech); High Energy Physics - Theory (hep-th); Quantum Physics (quant-ph)

Out-of-time-ordered (OTO) correlation functions have been proposed to describe the distribution or "scrambling" of information across a quantum state. In this work, we investigate both time-ordered and OTO correlation functions in the non-integrable, one-dimensional Bose-Hubbard model at high temperatures where well-defined quasiparticles cease to exist. Performing numerical simulations based on matrix product operators, we observe a linear light-cone spreading of quantum information in the OTO correlators. From our numerical data, we extract the speed of information propagation and the Lyapunov exponent, which we compare with predictions from holography. In contrast with the fast spreading of information, the thermalization of the system takes parametrically longer due to the slow diffusion of conserved quantities. Our numerical simulations demonstrate such slow hydrodynamic power-laws in the late time dynamics of the density correlation function. We furthermore propose two different interferometric schemes to approach the challenge of measuring time-ordered as well as OTO correlation functions in real space and time. Our protocols do not require an ancillary qubit and are respectively based on the local and global interference of two copies of the many-body state.