Spin Gradient Demagnetization Cooling of Ultracold Atoms

Medley, Patrick; Weld, David; Miyake, Hirokazu; Pritchard, David E.; Ketterle, Wolfgang

doi:10.1103/physrevlett.106.195301

Cited by 137 publications

(143 citation statements)

References 34 publications

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“…Negative temperatures describe equilibrated systems with population inversion and are well defined for systems like the Hubbard model where the energy has an upper bound [35]. They have been observed in spin systems [33] and localized ultracold atoms [34]. Assuming local thermalization, the observed U ↔ −U symmetry directly implies negative temperatures for repulsive interactions at long expansion times.…”

Section: Interacting Casementioning

confidence: 97%

Fermionic transport and out-of-equilibrium dynamics in a homogeneous Hubbard model with ultracold atoms

et al. 2012

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Transport properties are among the defining characteristics of many important phases in condensed matter physics. In the presence of strong correlations they are difficult to predict even for model systems like the Hubbard model. In real materials they are in general obscured by additional complications including impurities, lattice defects or multi-band effects. Ultracold atoms in contrast offer the possibility to study transport and out-of-equilibrium phenomena in a clean and well-controlled environment and can therefore act as a quantum simulator for condensed matter systems. Here we studied the expansion of an initially confined fermionic quantum gas in the lowest band of a homogeneous optical lattice. While we observe ballistic transport for non-interacting atoms, even small interactions render the expansion almost bimodal with a dramatically reduced expansion velocity. The dynamics is independent of the sign of the interaction, revealing a novel, dynamic symmetry of the Hubbard model.In solid state physics, transport properties are among the key observables, the most prominent example being the electrical conductivity, which e.g. allows to distinguish normal conductors from insulators or superconductors. Furthermore, many of today's most intriguing solid state phenomena manifest themselves in transport properties, examples including high-temperature superconductivity, giant magnetoresistance, quantum hall physics, topological insulators and disorder phenomena. Especially in strongly correlated systems, where the interactions between the conductance electrons are important, transport properties are difficult to calculate beyond the linear response regime. In general, predicting out-of-equilibrium fermionic dynamics represents an even harder problem than the prediction of static properties like the nature of the ground state. In real solids further complications arise due to the effects of e.g. impurities, lattice defects and phonons. These complications render an experimental investigation in a clean and well controlled ultracold atom system highly desirable. While the last years have seen dramatic progress in the control of quantum gases in optical lattices [1-3], a thorough understanding of the dynamics in these systems is still lacking. Genuine dynamical experiments can not only uncover new dynamic phenomena but are also essential to gain insight into the timescales needed to achieve equilibrium in the lattice [4,5] or to adiabatically load into the lattice [6,7].Using both bosonic and fermionic [8-10] atoms, it has become possible to simulate models of strongly interacting quantum particles, for which the Hubbard model [11] * ulrich.schneider@lmu.de is probably the most important example. A major advantage of these systems compared to real solids is the possibility to change all relevant parameters in real-time by e.g. varying laser intensities or magnetic fields. While first studies of dynamical properties of both bosonic and fermionic quantum gases [12][13][14] have already been performed, a remaining...

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Section: Interacting Casementioning

confidence: 97%

Fermionic transport and out-of-equilibrium dynamics in a homogeneous Hubbard model with ultracold atoms

et al. 2012

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“…It remains experimentally challenging to reach such low temperatures [53]. However, in view of two recent advances of new cooling techniques [54,55] to reach 0.35nK, the obstacles maybe overcame in the near future. Before reaching such low temperatures, the specific heat measurement [38,39] at high temperatures to determine the whole sets of Wilson loops order by order in J/T along the dashed line in Fig.1b could be performed easily.…”

Section: Experimental Realizations Of the Rh Models In The U(1) mentioning

confidence: 99%

Quantum magnetism of spinor bosons in optical lattices with synthetic non-Abelian gauge fields

2015

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We study quantum magnetism of interacting spinor bosons at integer fillings hopping in a square lattice in the presence of of non-Abelian gauge fields. In the strong coupling limit, it leads to the Rotated ferromagnetic Heisenberg model (RFHM) which is a new class of quantum spin model. We introduce Wilson loops to characterize frustrations and gauge equivalent classes. For a special equivalent class, we identify a new spin-orbital entangled commensurate ground state. It supports not only commensurate magnons, but also a new gapped elementary excitation: in-commensurate magnons with two gap minima continuously tuned by the SOC strength. At low temperatures, these magnons lead to dramatic effects in many physical quantities such as density of states, specific heat, magnetization, uniform susceptibility, staggered susceptibility and various spin correlation functions. The commensurate magnons lead to a pinned central peak in the angle resolved light or atom Bragg spectroscopy. However, the in-commensurate magnons split it into two located at their two gap minima. At high temperatures, the transverse spin structure factors depend on the SOC strength explicitly. The whole set of Wilson loops can be mapped out by measuring the specific heat at the corresponding orders in the high temperature expansion. We argue that one gauge may be realized in current experiments and other gauges may also be realized in near future experiments. The results achieved along the exact solvable line sets up the stage to investigate dramatic effects when tuning away from it by various means. We sketch the crucial roles to be played by these magnons at other equivalent classes, with spin anisotropic interactions and in the presence of finite magnetic fields. Various experimental detections of these new phenomena are discussed. Rotated Anti-ferromagnetic Heisenberg model are also briefly mentioned.

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“…Quite complementary, recent progress in optical lattices are making a real chance out of several theoretical proposals for realizing spin chains with cold atoms [8][9][10][11][12], though with some restrictions on the structure of the effective spin Hamiltonians actually attainable [13]. Moreover, different initial states can be realized in an optical lattice [14][15][16], and new cooling techniques [17] also provide the possibility of reaching temperatures in which the magnetic phases are not disturbed by thermal fluctuations and so the real magnetic ground state of the system becomes reachable.…”

Section: Introductionmentioning

confidence: 99%

Initializing an unmodulated spin chain to operate as a high-quality quantum data bus

et al. 2011

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We study the quality of state and entanglement transmission through quantum channels described by spin chains varying both the system parameters and the initial state of the channel. We consider a vast class of one-dimensional many-body models which contains some of the most relevant experimental realizations of quantum data-buses. In particular, we consider spin-1/2 XY and XXZ model with open boundary conditions. Our results show a significant difference between free-fermionic (non-interacting) systems (XY) and interacting ones (XXZ), where in the former case initialization can be exploited for improving the entanglement distribution, while in the latter case it also determines the quality of state transmission. In fact, we find that in non interacting systems the exchange with fermions in the initial state of the chain always has a destructive effect, and we prove that it can be completely removed in the isotropic XX model by initializing the chain in a ferromagnetic state. On the other hand, in interacting systems constructive effects can arise by scattering between hopping fermions and a proper initialization procedure. Remarkably our results are the first example in which state and entanglement transmission show maxima at different points as the interactions and initializations of spin chain channels are varied.

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Spin Gradient Demagnetization Cooling of Ultracold Atoms

Cited by 137 publications

References 34 publications

Fermionic transport and out-of-equilibrium dynamics in a homogeneous Hubbard model with ultracold atoms

Fermionic transport and out-of-equilibrium dynamics in a homogeneous Hubbard model with ultracold atoms

Quantum magnetism of spinor bosons in optical lattices with synthetic non-Abelian gauge fields

Initializing an unmodulated spin chain to operate as a high-quality quantum data bus

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