Reaching Fermi Degeneracy via Universal Dipolar Scattering

Aikawa, K.; Frisch, Albert; Mark, Manfred J.; Baier, Simon; Grimm, Rudolf; Ferlaino, Francesca

doi:10.1103/physrevlett.112.010404

Cited by 199 publications

(234 citation statements)

References 42 publications

(73 reference statements)

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“…It is essential to note that although the relevant interaction in most experiments with cold atomic gases is contact, increasing interest has been focused on the atoms with * chuanwei.zhang@utdallas.edu large magnetic moments that possess dipole-dipole interactions [17,20,21]. In fact, the Bose-Einstein condensation of several dipolar atoms such as Chromium [22][23][24], Dysprosium [25], and Erbium [26], as well as the degeneracy of a dipolar Fermi gas [27,28] have been observed in experiments.…”

Section: Introductionmentioning

confidence: 99%

Bright solitons in a two-dimensional spin-orbit-coupled dipolar Bose-Einstein condensate

Zhang

2015

Phys. Rev. A

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We study a two-dimensional spin-orbit-coupled dipolar Bose-Einstein condensate with repulsive contact interactions by both the variational method and the imaginary time evolution of the GrossPitaevskii equation. The dipoles are completely polarized along one direction in the 2D plane to provide an effective attractive dipole-dipole interaction. We find two types of solitons as the ground states arising from such attractive dipole-dipole interactions: a plane wave soliton with a spatially varying phase and a stripe soliton with a spatially oscillating density for each component. Both types of solitons possess smaller size and higher anisotropy than the soliton without spin-orbit coupling. Finally, we discuss the properties of moving solitons, which are nontrivial because of the violation of Galilean invariance.

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Section: Introductionmentioning

confidence: 99%

Bright solitons in a two-dimensional spin-orbit-coupled dipolar Bose-Einstein condensate

Zhang

2015

Phys. Rev. A

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“…Such broken symmetries have profound implications for the interesting topological defects [1]. We shall describe this state in a 3D magnetic dipolar Fermi gas composed of one hyperfine sate, which has been realized in the experimental system of 167 Er [17] recently. The direction of dipole moments can be fixed by applying an external magnetic field.…”

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confidence: 99%

“…Recently, degenerate dipolar Fermi gases witnessed rapid developments in both magnetic dipolar atoms (such as 167 Er [17,18] and 161 Dy [19,20] atoms) and polar molecules [21,22], stimulating tremendous interests in dipolar effects in many-body phases. The effects of the anisotropic dipolar interaction on the fermion many-body physics have been extensively investigated [23].…”

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confidence: 99%

Weyl Superfluidity in a Three-Dimensional Dipolar Fermi Gas

Liu

Yin

et al. 2015

Phys. Rev. Lett.

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Weyl superconductivity or superfluidity, a fascinating topological state of matter, features novel phenomena such as emergent Weyl fermionic excitations and anomalies. Here we report that an anisotropic Weyl superfluid state can arise as a low temperature stable phase in a 3D dipolar Fermi gas. A crucial ingredient of our model is a direction-dependent two-body effective attraction generated by a rotating external field. Experimental signatures are predicted for cold gases in radio-frequency spectroscopy. The finite temperature phase diagram of this system is studied and the transition temperature of the Weyl superfluidity is found to be within the experimental scope for atomic dipolar Fermi gases.Weyl superfluids or semimetals represent recent developments in generalizing topological phases from gapped to gapless systems (e.g., from topological insulators to semimetals), in condensed matter physics [1,2]. These Weyl states are characterized by the presence of two (or more) gapless Weyl points, which are topologically protected against small perturbations. The Weyl nodes lead to a variety of fascinating phenomena such as unusual surface states [3,4], Hall effects [5,6], and other transport features [7,8]. Finding electronic materials supporting Weyl states has attracted considerable interests [9]. There are many proposed potential candidate materials, such as the pyrochlore iridates [3], topological insulator multilayer structures [7,[10][11][12], as well as certain quasicrystals [13]. However, there is still no compelling experimental evidence for the observation of one. In the field of ultracold atoms, this phase was predicted to appear in spinorbit coupled Fermi gases [14,15]. This line of active research awaits for the future experimental breakthrough of synthesizing higher dimensional artificial spin-orbit coupling with controlled heating [16]. After all, the search for Weyl superconductors remains an open problem for both electronic and ultracold atomic systems.In this letter, we report the emergence of Weyl superfluidity in a 3D single-component dipolar Fermi gas with an effective attraction engineered by a rotating external field. Recently, degenerate dipolar Fermi gases witnessed rapid developments in both magnetic dipolar atoms (such as 167 Er [17,18] and 161 Dy [19,20] atoms) and polar molecules [21,22], stimulating tremendous interests in dipolar effects in many-body phases. The effects of the anisotropic dipolar interaction on the fermion many-body physics have been extensively investigated [23]. In particular, this provides the possibility of superfluid pairing between dipolar Fermi atoms in spinless or multicomponent systems [24][25][26][27] at low temperatures. For dipoles aligned parallel to the z direction, a p-wave superfluid state with the dominant p z symmetry was studied in a three-dimensional dipolar Fermi gas [28] and the competition between this superfluidity and nematic charge-density-wave (CDW) was also discussed [29]. For a dipolar Fermi gas confined in a 2D plane, superfluid states o...

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“…Our experimental procedure to create a degenerate Fermi gas of 167 Er atoms follows the one described in Ref. [18,19]. In brief, it comprises laser cooling in a narrow-line magneto-optical trap (MOT) [21] and direct evaporative cooling of a spin-polarized sample in an optical dipole trap (ODT) [18].…”

mentioning

confidence: 99%

“…[18,19]. In brief, it comprises laser cooling in a narrow-line magneto-optical trap (MOT) [21] and direct evaporative cooling of a spin-polarized sample in an optical dipole trap (ODT) [18]. Evaporative cooling, which was successfully used to reach Bose-Einstein condensation [22,23], relies on efficient thermalization.…”

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confidence: 99%

Anisotropic Relaxation Dynamics in a Dipolar Fermi Gas Driven Out of Equilibrium

et al. 2014

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We report on the observation of a large anisotropy in the rethermalization dynamics of an ultracold dipolar Fermi gas driven out of equilibrium. Our system consists of an ultracold sample of strongly magnetic 167 Er fermions, spin-polarized in the lowest Zeeman sublevel. In this system, elastic collisions arise purely from universal dipolar scattering. Based on cross-dimensional rethermalization experiments, we observe a strong anisotropy of the scattering, which manifests itself in a large angular dependence of the thermal relaxation dynamics. Our result is in good agreement with recent theoretical predictions. Furthermore, we measure the rethermalization rate as a function of temperature for different angles and find that the suppression of collisions by Pauli blocking is not influenced by the dipole orientation.PACS numbers: 03.75. Ss, 37.10.De, 51.60.+a, 67.85.Lm The behavior of any many-body system follows from the interactions of its constituent particles. In some cases of physical interest, importantly at ultralow temperature, where the de Broglie wavelength is the dominant length scale, these interactions can be simplified by appealing to the Wigner threshold laws [1,2]. These laws, which have been extensively studied for particles interacting via van der Waals forces, both in experiment and theory [3], identify the interactions via simple isotropic parameters such as a scattering length. However, for dipolar particles, the fundamental interaction is anisotropic and the system properties can depend on the orientation of the gas with respect to a particular direction in space. [4,5].One of the major strengths of ultracold matter is its susceptibility to being controlled by various means. Striking examples include traversing the BEC-BES crossover [6,7], welding atoms together into molecules [8,9], and inducing bosons to behave like fermions in one spatial dimension [10,11]. Most often, such control exploits the quantum mechanical nature of a many-body gas at ultralow temperature, and arises from the manipulation of isotropic scattering between constituent particles. However, in the case of dipolar particles the scattering is intrinsically anisotropic, affording novel opportunities to control the behavior of the gas. For example, the anisotropic d-wave collapse of a Bose-Einstein condensate of magnetic atoms [12,13] and the deformation of the Fermi sphere in a dipolar Fermi gas [14] have been observed. These phenomena rely on the collective behavior of all the particles, occurring according to their mean field energy.Distinct from such many-body effects, dipoles can also influence the properties of the gas via two-body scattering. Since scattering of dipoles is highly anisotropic, properties that require the collisional exchange of energy and momentum between the atoms, such as sound propagation, viscosity, and virial coefficients [15], will be influenced by the presence of dipoles. In particular, differential cross sections of dipolar particles are highly anisotropic, depending on both the initial, as ...

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Reaching Fermi Degeneracy via Universal Dipolar Scattering

Cited by 199 publications

References 42 publications

Bright solitons in a two-dimensional spin-orbit-coupled dipolar Bose-Einstein condensate

Bright solitons in a two-dimensional spin-orbit-coupled dipolar Bose-Einstein condensate

Weyl Superfluidity in a Three-Dimensional Dipolar Fermi Gas

Anisotropic Relaxation Dynamics in a Dipolar Fermi Gas Driven Out of Equilibrium

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