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Families of dark solitons exist in superfluid Fermi gases. The energy-velocity dispersion and number of depleted particles completely determine the dynamics of dark solitons on a slowly varying background density. For the unitary ...
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Families of dark solitons exist in superfluid Fermi gases. The energy-velocity dispersion and number of depleted particles completely determine the dynamics of dark solitons on a slowly varying background density. For the unitary Fermi gas, we determine these relations from general scaling arguments and conservation of local particle number. We find solitons to oscillate sinusoidally at the trap frequency reduced by a factor of 1/N/I Numerical integration of the time-dependent Bogoliubov–de Gennes equation determines spatial profiles and soliton-dispersion relations across the BEC-BCS crossover, and proves consistent with the scaling relations at unitarity.
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An experiment was performed to measure transverse sound resonances in a square slab of aerogel filled with liquid He-4. Resonances have been observed both in the superfluid and normal phase. The dynamics of the system was modelled...
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An experiment was performed to measure transverse sound resonances in a square slab of aerogel filled with liquid He-4. Resonances have been observed both in the superfluid and normal phase. The dynamics of the system was modelled by combining the equations of two-fluid hydrodynamics of helium with those of elasticity of aerogel. (C) 2003 Elsevier Science B.V. All rights reserved. [References: 3]
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We show that spinor Bose gases subject to a quadratic Zeeman effect exhibit coexisting superfluidity and spin superfluidity, and study the interplay between these two distinct types of superfluidity. To illustrate that the basic p...
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We show that spinor Bose gases subject to a quadratic Zeeman effect exhibit coexisting superfluidity and spin superfluidity, and study the interplay between these two distinct types of superfluidity. To illustrate that the basic principles governing these two types of superfluidity are the same, we describe the magnetization and particle-density dynamics in a single hydrodynamic framework. In this description spin and mass supercurrents are driven by their respective chemical potential gradients. As an application, we propose an experimentally accessible stationary state, where the two types of supercurrents counterflow and cancel each other, thus resulting in no mass transport. Furthermore, we propose a straightforward setup to probe spin superfluidity by measuring the in-plane magnetization angle of the whole cloud of atoms. We verify the robustness of these findings by evaluating the four-magnon collision time, and find that the time scale for coherent (superfluid) dynamics is separated from that of the slower incoherent dynamics by one order of magnitude. Comparing the atom and magnon kinetics reveals that while the former can be hydrodynamic, the latter is typically collisionless under most experimental conditions. This implies that, while our zero-temperature hydrodynamic equations are a valid description of spin transport in Bose gases, a hydrodynamic description that treats both mass and spin transport at finite temperatures may not be readily feasible.
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We compare recent experimental results [Science 375, 528 (2022)] of the superfluid unitary Fermi gas near the critical temperature with a thermodynamic model based on the elementary excitations of the system. We find good agreemen...
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We compare recent experimental results [Science 375, 528 (2022)] of the superfluid unitary Fermi gas near the critical temperature with a thermodynamic model based on the elementary excitations of the system. We find good agreement between experimental data and our theory for several quantities such as first sound, second sound, and superfluid fraction. We also show that mode mixing between first and second sound occurs. Finally, we characterize the response amplitude to a density perturbation: Close to the critical temperature both first and second sound can be excited through a density perturbation, whereas at lower temperatures only the first sound mode exhibits a significant response.
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We investigate the ground state properties of Fermi gases in a planar array of one-dimensional potential tubes with spin-orbit coupling where the motion of atoms is free in the (x) over cap -direction and the tunneling between nea...
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We investigate the ground state properties of Fermi gases in a planar array of one-dimensional potential tubes with spin-orbit coupling where the motion of atoms is free in the (x) over cap -direction and the tunneling between nearest tubes in the (y) over cap -direction is permitted. By using the mean-field method, the phase diagrams of the system at the dimensional crossover from quasi-one dimension to quasi-two dimensions is obtained. We find the existence of the topological state and Majorana mode in the weak tunneling case, and a rich phase diagram including two kinds of nodal superfluid phase and gapped superfluid phase, in the opposite case. The results show that topological pairing is favored in quasi-one dimension while nodal pairing state is favored in quasi-two dimensions.
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Ultracold gases composed of lanthanide atoms are characterized by long-range dipolar interactions. These have now been exploited to observe quantized vortices in a dipolar condensate through the manipulation of the atoms by rotati...
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Ultracold gases composed of lanthanide atoms are characterized by long-range dipolar interactions. These have now been exploited to observe quantized vortices in a dipolar condensate through the manipulation of the atoms by rotating external magnetic fields. Quantized vortices are a prototypical feature of superfluidity that have been observed in multiple quantum gas experiments. But the occurrence of vortices in dipolar quantum gases-a class of ultracold gases characterized by long-range anisotropic interactions-has not been reported yet. Here we exploit the anisotropic nature of the dipole-dipole interaction of a dysprosium Bose-Einstein condensate to induce angular symmetry breaking in an otherwise cylindrically symmetric pancake-shaped trap. Tilting the magnetic field towards the radial plane deforms the cloud into an ellipsoid, which is then set into rotation. At stirring frequencies approaching the radial trap frequency, we observe the generation of dynamically unstable surface excitations, which cause angular momentum to be pumped into the system through vortices. Under continuous rotation, the vortices arrange into a stripe configuration along the field, in close agreement with numerical simulations.
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Using epsilon expansion technique proposed by Nishida and Son [Phys. Rev. Lett. 97, 050403 (2006)] we derive an effective Lagrangian (Ginzburg-Landau-type functional) of the degenerate unitary Fermi gas to the next-to-leading orde...
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Using epsilon expansion technique proposed by Nishida and Son [Phys. Rev. Lett. 97, 050403 (2006)] we derive an effective Lagrangian (Ginzburg-Landau-type functional) of the degenerate unitary Fermi gas to the next-to-leading order in epsilon. It is demonstrated that for many realistic situations it is sufficient to retain leading order terms in the derivative expansion. The functional is used to study vortex structure in the symmetric gas, and interface between normal and superfluid phases in the polarized gas. Typical vortex size, r(0)k(F)=0.92, where k(F) is Fermi momentum, agrees well with results of previous work [A. Bulgac and Y. Yu, Phys. Rev. Lett. 91, 190404 (2003)]. Surface free energy is about 3 times larger than the value previously quoted in the literature.
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We describe recent progress in Quantum Monte Carlo calculations of nuclear structure and reactions. Significant advances have been made recently in understanding the nuclear Hamiltonian, including realistic two- and three-nucleon ...
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We describe recent progress in Quantum Monte Carlo calculations of nuclear structure and reactions. Significant advances have been made recently in understanding the nuclear Hamiltonian, including realistic two- and three-nucleon interactions. We describe recent progress in solving the nuclear Hamiltonian for two important long-standing problems in nuclear theory: (1) low-energy scattering in n-He-4 and the spin-orbit splitting obtained with microscopic Hamiltonians, and (2) the pairing gap in low-density neutron matter. Accurate calculations of both quantities are fundamental in understanding nuclei from the underlying microscopic Hamiltonian.
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We investigate pairing in a two-component degenerate gas of trapped fermionic Li-6 atoms at a broad Feshbach resonance by in-situ imaging of real-space density distributions. From even mixtures of the two spin components, we measu...
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We investigate pairing in a two-component degenerate gas of trapped fermionic Li-6 atoms at a broad Feshbach resonance by in-situ imaging of real-space density distributions. From even mixtures of the two spin components, we measured the beta factor, describing the universal energy of strongly interacting paired fermions. In uneven spin mixtures, pairing and corresponding phases show a temperature dependence that is consistent with a phase diagram having a tricritical point. At the lowest temperatures, an unpolarized core separates from the excess unpaired atoms by a sharp boundary, which is consistent with a phase separation driven by a first-order phase transition. Moreover, the unpolarized core deforms with increasing polarization, in violation of local density approximation (LDA). In contrast, at higher but still degenerate temperatures, an unpolarized central core remains up to a critical polarization, but does not deform. In this case, the boundaries are not sharp, indicating a partially-polarized shell between the core and the unpaired atoms, consistent with a second-order phase boundary.
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We carry out a systematic analytic investigation of stationary and cylindrically symmetric vortex configurations for simple models representing an incompressible nonrelativistic superconductor in a background, which is rigidly rot...
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We carry out a systematic analytic investigation of stationary and cylindrically symmetric vortex configurations for simple models representing an incompressible nonrelativistic superconductor in a background, which is rigidly rotating with the angular velocity Omega. It is shown that although the magnetic and kinetic contributions to the energy per unit length of such a Vortex are separately modified by the background angular velocity, its effect on the total energy per unit length cancels out. For a type II superconductor threaded by a parallel array of such vortices, this result implies that the conventionally defined local magnetic field strength H will not be equal to the local space average < B > of the magnetic induction B las has previously been suggested), but instead that H will simply be equal to the London field B-L= - (2m/q)Omega (where m and q are the mass and charge of the condensate particles). [References: 5]
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