Arxiv Selection Dec 2018
Dec 1-Dec 7 Zehan Li, Dec 8-Dec 14 Jiansong Pan, Dec 15-Dec 21 Ahmet Keles, Dec 22- Dec 28 Haiping Hu
Contents
Dec. 14
arXiv:1812.05278 [pdf, ps, other]
Theoretical Reproduction of Fractional Quantum Hall Resistivity and Quasiparticle Energy Gaps
Jongbae Hong
Comments: 4 pages, 4 figures, 1 table
Subjects: Strongly Correlated Electrons (cond-mat.str-el)
Experimental fractional quantum Hall resistivity and quasiparticle energy gaps are reproduced theoretically by considering correlated many-electron dynamics in incompressible strips under nonequilibrium transport. Plateau width and chemical potential are determined as well as plateau positions. Electrostatic confining potential of the incompressible strip causes deformed cycloidal electron motion. The confining potential is replaced by an image electron with the same spin, which gives rise to a composite boson of spin unity as a quasiparticle in describing current ow. Zeeman effect for the total spin of correlated quasiparticles further splits the Landau level, and forms the energy gaps and plateaus in Hall resistivity.
Dec. 13
arXiv:1812.04630 (cross-list from quant-ph) [pdf, other]
Exploring the unification of quantum theory and general relativity with a Bose-Einstein condensate
Richard Howl, Roger Penrose, Ivette Fuentes
Comments: 49 pages, 10 figures
Subjects: Quantum Physics (quant-ph); Quantum Gases (cond-mat.quant-gas); General Relativity and Quantum Cosmology (gr-qc)
Despite almost a century worth of study, it is still unclear how general relativity (GR) and quantum theory (QT) should be unified into a consistent theory. The conventional approach is to retain the foundational principles of QT, such as the superposition principle, and modify GR. This is referred to as 'quantizing gravity', resulting in a theory of 'quantum gravity'. The opposite approach is 'gravitizing QT' where we attempt to keep the principles of GR, such as the equivalence principle, and consider how this leads to modifications of QT. What we are most lacking in understanding which route to take, if either, is experimental guidance. Here we consider using a Bose-Einstein condensate (BEC) to search for clues. In particular, we study how a single BEC in a superposition of two locations could test a gravitizing QT proposal where wavefunction collapse emerges from a unified theory as an objective process, resolving the measurement problem of QT. Such a modification to QT due to general relativistic principles is testable at the Planck mass scale, which is much closer to experiments than the Planck length scale where quantum, general relativistic effects are traditionally anticipated in quantum gravity theories. Furthermore, experimental tests of this proposal should be simpler to perform than recently suggested experiments that would test the quantizing gravity approach in the Newtonian gravity limit by searching for entanglement between two massive systems that are both in a superposition of two locations.
Dec. 12
arXiv:1812.04001 (cross-list from quant-ph) [pdf, other]
A supersolid-based gravimeter in a ring cavity
Karol Gietka, Farokh Mivehvar, Helmut Ritsch
Comments: 9 pages, 6 figures, corrected line breaks
Subjects: Quantum Physics (quant-ph); Quantum Gases (cond-mat.quant-gas)
We propose a novel type of composite light-matter interferometer based on a supersolid-like phase of a driven Bose-Einstein condensate coupled to a pair of degenerate counterpropagating modes of an optical ring cavity. The supersolid-like condensate under the influence of the gravity drags the cavity optical potential with itself, thereby changing the relative phase of the two cavity modes. Monitoring the phase evolution of the cavity output fields thus allows for a nondestructive measurement of the gravitational acceleration. We show that the sensitivity of the proposed gravimeter exhibits Heisenberg-like scaling with respect to the atom number. As the relative phase of the cavity modes is insensitive to photon losses, the gravimeter is robust against these deleterious effects. For state-of-the-art experimental parameters, the sensitivity of such a gravimeter could be of the order of 10−10--10−8 for a condensate of a half a million atoms with long measurement times.
Dec. 11
arXiv:1812.03875 [pdf, ps, other]
Observation of atom-number fluctuations in optical lattices via quantum collapse and revival dynamics
Tianwei Zhou, Kaixiang Yang, Zijie Zhu, Xudong Yu, Shifeng Yang, Wei Xiong, Xiaoji Zhou, Xuzong Chen, Chen Li, Jörg Schmiedmayer, Xuguang Yue, Yueyang Zhai
Comments: 7 pages, 3 figures
Subjects: Quantum Gases (cond-mat.quant-gas); Atomic Physics (physics.atom-ph); Quantum Physics (quant-ph)
Using the quantum collapse and revival phenomenon of a Bose--Einstein condensate in three-dimensional optical lattices, the atom number statistics on each lattice site are experimentally investigated. We observe an interaction driven time evolution of on-site number fluctuations in a constant lattice potential with the collapse and revival time ratio as the figure of merit. Through a shortcut loading procedure, we prepare a three-dimensional array of coherent states with Poissonian number fluctuations. The following dynamics clearly show the interaction effect on the evolution of the number fluctuations from Poissonian to sub-Poissonian. Our method can be used to create squeezed states which are important in precision measurement.
arXiv:1812.03756 [pdf, other]
Topological Gapless Matters in Three-dimensional Ultracold Atomic Gases
Yong Xu
Comments: 22 pages, 13 figures. An invited review article for the special issue on recent advances in topological materials of Frontiers of Physics. Comments are welcome
Subjects: Quantum Gases (cond-mat.quant-gas); Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
Three-dimensional topological gapless matters with gapless degeneracies protected by a topological invariant defined over a closed manifold in momentum space have attracted considerable interest in various fields ranging from condensed matter materials to ultracold atomic gases. As a highly controllable and disorder free system, ultracold atomic gases provide a versatile platform to simulate topological gapless matters. Here, the current progress in studies of topological gapless phenomena in three-dimensional cold atom systems is summarized in the review. It is mainly focused on Weyl points, structured (type-II) Weyl points, Dirac points, nodal rings and Weyl exceptional rings in cold atoms. Since interactions in cold atoms can be controlled via Feshbach resonances, the progress in both superfluids for attractive interactions and non-interacting cold atom gases is reviewed.
Dec. 10
arXiv:1812.03064 [pdf, other]
Observation of Atom Number Fluctuations in a Bose-Einstein Condensate
M.A.Kristensen, M. B. Christensen, M.Gajdacz, M.Iglicki, K.Pawłowski, C.Klempt, J.F.Sherson, K.Rzążewski, A.J.Hilliard, J.J.Arlt
Comments: Main text: 5 pages, 4 figures. Supplemental Information: 3 figures, 1 pages
Subjects: Quantum Gases (cond-mat.quant-gas)
Fluctuations are a key property of both classical and quantum systems. While the fluctuations are well understood for many quantum systems at zero temperature, the case of an interacting quantum system at finite temperature still poses numerous challenges. Despite intense theoretical investigations of atom number fluctuations in Bose-Einstein condensates (BECs), their amplitude in experimentally relevant interacting systems is still poorly understood. Moreover, technical limitations have prevented their experimental observation to date. Here we report the first observation of these fluctuations. Our experiments are based on a stabilization technique, which allows for the preparation of ultracold thermal clouds at the shot noise level, thereby eliminating numerous technical noise sources. Furthermore, we make use of the correlations established by the evaporative cooling process to precisely determine the fluctuations and the sample temperature. This allows us to observe a telltale signature: the sudden increase in fluctuations of the condensate atom number close to the critical temperature.
Dec. 7
arXiv:1812.02701 (cross-list from cond-mat.stat-mech) [pdf, other]
Kinetic theory of spin superdiffusion in Heisenberg spin chains at high temperature
Sarang Gopalakrishnan, Romain Vasseur
Comments: 6 pages, 1 figure
Subjects: Statistical Mechanics (cond-mat.stat-mech); Quantum Gases (cond-mat.quant-gas); Strongly Correlated Electrons (cond-mat.str-el); Quantum Physics (quant-ph)
We address the nature of spin transport in the integrable XXZ spin chain, focusing on the isotropic Heisenberg limit. We calculate the diffusion constant using a kinetic picture based on generalized hydrodynamics: we find that it diverges, and show that a self-consistent treatment of this divergence gives superdiffusion, with an effective time-dependent diffusion constant that scales as D(t) ∼ t 1/3 . This exponent had previously been observed in large-scale numerical simulations, but had not been theoretically explained. Our results also make clear why the anomalous diffusion in the present case is a qualitatively different phenomenon from Levy flights and other phenomena in random systems. We briefly discuss XXZ models with easy-axis anisotropy ∆ > 1; for these our treatment predicts diffusion, with a diffusion constant D that saturates at large anisotropy, and diverges as the Heisenberg limit is approached, as D ∼ (∆ − 1)−1/2 .
Dec. 6
arXiv:1812.01976 [pdf, other]
Spin-charge separation in strongly interacting multicomponent few-body systems
Rafael Emilio Barfknecht, Angela Foerster, Nikolaj Thomas Zinner
Comments: 11 pages, 8 figures
Subjects: Quantum Gases (cond-mat.quant-gas); Quantum Physics (quant-ph)
The effect of spin-charge separation is known to happen in one-dimensional many-body systems in the presence of interactions between particles. In a few-body regime, however, little is known about this phenomenon. To address this problem, we describe the time-evolution of a small system of strongly interacting fermions with SU(N) symmetry after a sudden change in the trapping geometry. The presence of strong contact interactions allows for a mapping between a multicomponent repulsive gas and an effective spin chain, where the internal degrees of freedom of the atoms play the role of different spin projections. This model captures the dynamical behavior of the system by taking into account a set of time-dependent exchange coefficients, which are determined by the instantaneous spatial densities of the system. We show how changing the trapping potential influences the spatial distribution of each atomic species in the ground state of the spin chain. We then obtain the dynamics of the spin densities after a sudden change in the trap. Even at the few-body level, the excitation spectrum for this quantity presents clear separate signatures of both spin and charge dynamics. Moreover, as the number of internal components is increased, we show that the spin excitations vanish, and the dynamics can be predicted by the excitation frequencies expected for a gas of impenetrable bosons. Additionally, we include the description of the dynamics under the same quench protocol in a system where SU(N) symmetry is broken.
Dec. 5
arXiv:1812.00387 [pdf, other]
The four-body scale in universal few-boson systems
Betzalel Bazak, Johannes Kirscher, Sebastian König, Manuel Pavón Valderrama, Nir Barnea, Ubirajara van Kolck
Subjects: Quantum Gases (cond-mat.quant-gas); Nuclear Theory (nucl-th); Quantum Physics (quant-ph)
The role of an intrinsic four-body scale in universal few-boson systems is the subject of active debate. We study these systems within the framework of effective field theory. For systems of up to six bosons we establish that no four-body scale appears at leading order. However, we find that at next-to-leading order a four-body force is needed to obtain renormalized results for binding energies. With the associated parameter fixed to the binding energy of the four-boson system, this force is shown to renormalize the five- and six-body systems as well. As a specific example, calculations are presented for clusters of helium atoms. Our results apply however more generally to other few-body systems governed by a large scattering length, such as low-energy properties of light nuclei and halo states the character of which does not depend on the detailed structure of their cores.
Dec. 4
arXiv:1812.00473 [pdf, other]
Quantum vortex reconnections: crossover from interaction to driven regimes
Luca Galantucci, Andrew W. Baggaley, Nick G. Parker, Carlo F. Barenghi
Comments: 9 pages, 8 Figures main manuscript; 7 pages, 3 Figures Supporting Information
Subjects: Quantum Gases (cond-mat.quant-gas)
Reconnections of coherent filamentary structures play a key role in the dynamics of fluids, redistributing energy and helicity among the length scales, triggering dissipative effects and inducing fine-scale mixing. Unlike ordinary (classical) fluids where vorticity is a continuous field, in superfluid helium and in atomic Bose-Einstein condensates (BECs) vorticity takes the form of isolated quantised vortex lines, which are conceptually easier to study. New experimental techniques now allow visualisation of individual vortex reconnections in helium and condensates. It has long being suspected that reconnections obey universal laws, particularly a universal scaling with time of the minimum distance between vortices δ. Here we perform a comprehensive analysis of this scaling across a range of scenarios relevant to superfluid helium and trapped condensates, combining our own numerical simulations with the previous results in the literature. We reveal that the scaling exhibit two distinct regimes: a δ ∼ t 1/2 scaling arising from the mutual interaction of the reconnecting strands and a δ ∼ t scaling when extrinsic factors drive the individual vortices
Dec. 3
arXiv:1811.12743 [pdf, ps, other]
Superfluidity in dipolar binary Bose mixtures
Abdelaali Boudjemaa
Comments: 7 pages, 4 figures
Subjects: Quantum Gases (cond-mat.quant-gas)
We study the superfluidity and the coherence in dipolar binary Bose mixtures using the hydrodynamic approach. Useful analytical formula for the excitations spectrum, the correlation function and the superfluid fraction are derived. We find that in the case of highly imbalanced mixture, the superfluidity can occur in the dilute component only at extremely low temperatures. The behavior of the first-order correlation function for both dipolar and nondipolar Bose mixtures is deeply analyzed. Then we face the two-dimensional case which encodes a non-trivial physics due to the roton modes.
