Search results for "Fluidity"
showing 10 items of 226 documents
Exploiting Coherence in Nonlinear Spin-Superfluid Transport
2017
We show how the interference between superfluid spin currents can endow spin circuits with coherent logic functionality. While the hydrodynamic aspects of the linear-response collective spin transport obviate interference features, we focus on the nonlinear regime, where the critical supercurrent is sensitive to the phase accumulated by the condensate in a loop geometry. We propose to control this phase by electrical gating, tuning the spin-condensate coherence length. The nonlinear aspects of the spin superfluidity thus naturally lend themselves to the construction of logic gates, uniquely exploiting the coherence of collective spin currents. Vice versa, this functionality can be used to r…
Scissors modes of two-component degenerate gases: Bose-Bose and Bose-Fermi mixtures
2003
We investigate the scissors modes in binary mixtures of degenerate dilute quantum gases, for both Bose-Bose and Bose-Fermi mixtures. For the latter we consider both the superfluid and normal hydrodynamic and collisionless regimes. We analyze the dependence of the frequencies of the scissors modes and their character as a function of the Bose-Fermi coupling and the trap geometry. We show that the scissors mode can reveal a clear trace of the hydrodynamic behavior of the Fermi gas.
Signatures of superfluidity for Feshbach-resonant Fermi gases
2004
We consider atomic Fermi gases where Feshbach resonances can be used to continuously tune the system from weak to strong interaction regime, allowing to scan the whole BCS-BEC crossover. We show how a probing field transferring atoms out of the superfluid can be used to detect the onset of the superfluid transition in the high-$T_c$ and BCS regimes. The number of transferred atoms, as a function of the energy given by the probing field, peaks at the gap energy. The shape of the peak is asymmetric due to the single particle excitation gap. Since the excitation gap includes also a pseudogap contribution, the asymmetry alone is not a signature of superfluidity. Incoherent nature of the non-con…
Fermion pairing with spin-density imbalance in an optical lattice
2006
We consider pairing in a two-component atomic Fermi gas, in a three-dimensional optical lattice, when the components have unequal densities, i.e. the gas is polarized. We show that a superfluid where the translational symmetry is broken by a finite Cooper pair momentum, namely an FFLO-type state, minimizes the Helmholtz free energy of the system. We demonstrate that such a state is clearly visible in the observable momentum distribution of the atoms, and analyze the dependence of the order parameter and the momentum distribution on the filling fraction and the interaction strength.
Bloch oscillations in Fermi gases
2003
The possibility of Bloch oscillations for a degenerate and superfluid Fermi gas of atoms in an optical lattice is considered. For a one-component degenerate gas the oscillations are suppressed for high temperatures and band fillings. For a two-component gas the Landau criterion is used for specifying the regime where Bloch oscillations of the superfluid may be observed. We show how the amplitude of Bloch oscillations varies along the BCS-BEC crossover.
Sound velocity and dimensional crossover in a superfluid Fermi gas in an optical lattice
2005
We study the sound velocity in cubic and non-cubic three-dimensional optical lattices. We show how the van Hove singularity of the free Fermi gas is smoothened by interactions and eventually vanishes when interactions are strong enough. For non-cubic lattices, we show that the speed of sound (Bogoliubov-Anderson phonon) shows clear signatures of dimensional crossover both in the 1D and 2D limits.
Formation of spatial shell structures in the superfluid to Mott insulator transition
2006
International audience; We report on the direct observation of the transition from a compressible superfluid to an incompressible Mott insulator by recording the in-trap density distribution of a Bosonic quantum gas in an optical lattice. Using spatially selective microwave transitions and spin changing collisions, we are able to locally modify the spin state of the trapped quantum gas and record the spatial distribution of lattice sites with different filling factors. As the system evolves from a superfluid to a Mott insulator, we observe the formation of a distinct shell structure, in good agreement with theory.
Co-existence and shell structures of several superfluids in trapped three-component Fermi mixtures
2006
We study the properties of a trapped interacting three component Fermi gas. We assume that one of the components can have a different mass from the other two. We calculate the different phases of the three component mixture and find a rich variety of different phases corresponding to different pairing channels, and simple ways of tuning the system from one phase to another. In particular, we predict co-existence of several different superfluids in the trap, forming a shell structure, and phase transitions from this mixture of superfluids to a single superfluid when the system parameters or temperature is varied. Such shell structures realize superfluids with a non-trivial spatial topology a…
Quasiparticles, coherence and nonlinearity: exact simulations of RF-spectroscopy of strongly interacting one-dimensional Fermi gases
2008
We consider RF-spectroscopy of ultracold Fermi gases by exact simulations of the many-body state and the coherent dynamics in one dimension. Deviations from the linear response sum rule result are found to suppress the pairing contribution to the RF line shifts. We compare the coherent rotation and quasiparticle descriptions of RF-spectroscopy which are analogous to NMR experiments in superfluid $^3$He and tunneling in solids, respectively. We suggest that RF-spectroscopy in ultracold gases provides an interesting crossover between these descriptions that could be used for studying decoherence in quantum measurement, in the context of many-body quantum states.
The growth of atomically rough 4He crystals
1986
We have studied the growth of atomically rough bcc and hcp4He crystals from the superfluid phase for temperaturesT>0.9 K. The growth coefficient displays a temperature dependence which can be represented bym 4 K∝ $$e^{\Delta E/k_B T} $$ . The parameter ΔE is found to be in close agreement with the energy gap of rotons, suggesting that these thermal excitations dominate the growth kinetics. Besides, the absolute value of the growth coefficient depends on crystal orientation, with an anisotropy for the hcp phase of about a factor of 2.5 between the $$\left\{ {10\bar 10} \right\}$$ and {0001} planes.