High-temperature atomic superfluidity in lattice Bose-Fermi mixtures
International Nuclear Information System (INIS)
We consider atomic Bose-Fermi mixtures in optical lattices and study the superfluidity of fermionic atoms due to s-wave pairing induced by boson-fermion interactions. We prove that the induced fermion-fermion coupling is always attractive if the boson-boson on-site interaction is repulsive, and predict the existence of an enhanced BEC-BCS crossover as the strength of the lattice potential is varied. We show that for direct on-site fermion-fermion repulsion, the induced attraction can give rise to superfluidity via s-wave pairing at striking variance with the case of pure systems of fermionic atoms with direct repulsive interactions
High-temperature atomic superfluidity in lattice Bose-Fermi mixtures.
Illuminati, Fabrizio; Albus, Alexander
2004-08-27
We consider atomic Bose-Fermi mixtures in optical lattices and study the superfluidity of fermionic atoms due to s-wave pairing induced by boson-fermion interactions. We prove that the induced fermion-fermion coupling is always attractive if the boson-boson on-site interaction is repulsive, and predict the existence of an enhanced BEC-BCS crossover as the strength of the lattice potential is varied. We show that for direct on-site fermion-fermion repulsion, the induced attraction can give rise to superfluidity via s-wave pairing at striking variance with the case of pure systems of fermionic atoms with direct repulsive interactions. PMID:15447082
Işkın, Menderes; Subaşı, Ahmet Levent
2012-01-01
PHYSICAL REVIEW A 87, 063627 (2013) Topological superfluid phases of an atomic Fermi gas with in- and out-of-plane Zeeman fields and equal Rashba-Dresselhaus spin-orbit coupling M. Iskin1 and A. L. Subas¸ı2 1Department of Physics, Koc¸ University, Rumelifeneri Yolu, 34450 Sarıyer, Istanbul, Turkey 2Department of Physics, Faculty of Science and Letters, Istanbul Technical University, 34469 Maslak, Istanbul, Turkey (Received 16 November 2012; revised manuscript received 14 May...
Study of superfluid Bose-Fermi mixture
Laurent, Sebastien; Delehaye, Marion; Jin, Shuwei; Pierce, Matthieu; Yefsah, Tarik; Chevy, Frederic; Salomon, Christophe
2016-05-01
Using fermionic and bosonic isotopes of lithium we produce and study ultracold Bose-Fermi mixtures. First in a low temperature counterflow experiment, we measure the critical velocity of the system in the BEC-BCS crossover. Around unitarity, we observe a remarkably high superfluid critical velocity which reaches the sound velocity of the strongly interacting Fermi gas. Second, when we increase the temperature of the system slightly above the superfluid transitions we observe an unexpected phase locking of the oscillations of the clouds induced by dissipation. Finally, as suggested in, we explore the nature of the superfluid phase when we impose a spin polarization in the situation where the mean field potential created by the bosons on the fermions tends to cancel out the trapping potential of the latter.
Phase Separation in Bose-Fermi-Fermi Mixtures as a Probe of Fermi Superfluidity
Bhongale, S. G.; Pu, Han
2008-01-01
We study the phase diagram of a mixture of Bose-Einstein condensate and a two-component Fermi gas. In particular, we identify the regime where the homogeneous system becomes unstable against phase separation. We show that, under proper conditions, the phase separation phenomenon can be exploited as a robust probe of Fermi superfluid.
Towards Quantum Turbulence in Cold Atomic Fermionic Superfluids
Bulgac, Aurel; Wlazłowski, Gabriel
2016-01-01
Fermionic superfluids provide a new realization of quantum turbulence, accessible to both experiment and theory, yet relevant to both cold atoms and nuclear astrophysics. In particular, the strongly interacting Fermi gas realized in cold-atom experiments is closely related to dilute neutron matter in the neutron star crust. Unlike the liquid superfluids 4He (bosons) and 3He (fermions), where quantum turbulence has been studied in laboratory for decades, quantum gases, and in particular superfluid Fermi gases stand apart for a number of reasons. Fermi gases admit a rather reliable microscopic description based on density functional theory which describes both static and dynamical phenomena. Cold atom experiments demonstrate exquisite control over particle number, spin polarization, density, temperature, and interacting strength. Topological defects such as domain walls and quantized vortices, which lie at the heart of quantum turbulence, can be created and manipulated with time-dependent external potentials, a...
Theory of ultracold atomic Fermi gases
International Nuclear Information System (INIS)
The physics of quantum degenerate atomic Fermi gases in uniform as well as in harmonically trapped configurations is reviewed from a theoretical perspective. Emphasis is given to the effect of interactions that play a crucial role, bringing the gas into a superfluid phase at low temperature. In these dilute systems, interactions are characterized by a single parameter, the s-wave scattering length, whose value can be tuned using an external magnetic field near a broad Feshbach resonance. The BCS limit of ordinary Fermi superfluidity, the Bose-Einstein condensation (BEC) of dimers, and the unitary limit of large scattering length are important regimes exhibited by interacting Fermi gases. In particular, the BEC and the unitary regimes are characterized by a high value of the superfluid critical temperature, on the order of the Fermi temperature. Different physical properties are discussed, including the density profiles and the energy of the ground-state configurations, the momentum distribution, the fraction of condensed pairs, collective oscillations and pair-breaking effects, the expansion of the gas, the main thermodynamic properties, the behavior in the presence of optical lattices, and the signatures of superfluidity, such as the existence of quantized vortices, the quenching of the moment of inertia, and the consequences of spin polarization. Various theoretical approaches are considered, ranging from the mean-field description of the BCS-BEC crossover to nonperturbative methods based on quantum Monte Carlo techniques. A major goal of the review is to compare theoretical predictions with available experimental results.
Exciting Quantized Vortex Rings in a Superfluid Unitary Fermi Gas
Bulgac, Aurel
2014-03-01
In a recent article, Yefsah et al., Nature 499, 426 (2013) report the observation of an unusual quantum excitation mode in an elongated harmonically trapped unitary Fermi gas. After phase imprinting a domain wall, they observe collective oscillations of the superfluid atomic cloud with a period almost an order of magnitude larger than that predicted by any theory of domain walls, which they interpret as a possible new quantum phenomenon dubbed ``a heavy soliton'' with an inertial mass some 50 times larger than one expected for a domain wall. We present compelling evidence that this ``heavy soliton'' is instead a quantized vortex ring by showing that the main aspects of the experiment can be naturally explained within an extension of the time-dependent density functional theory (TDDFT) to superfluid systems. The numerical simulations required the solution of some 260,000 nonlinear coupled time-dependent 3-dimensional partial differential equations and was implemented on 2048 GPUs on the Cray XK7 supercomputer Titan of the Oak Ridge Leadership Computing Facility.
Superfluidity of heated Fermi systems in the static fluctuation approximation
Energy Technology Data Exchange (ETDEWEB)
Khamzin, A. A., E-mail: airat.khamzin@rambler.ru [Kazan (Volga Region) Federal University, Institute of Physics (Russian Federation); Nikitin, A. S.; Sitdikov, A. S. [Kazan State Power Engineering University (KSPEU) (Russian Federation)
2015-10-15
Superfluidity properties of heated finite Fermi systems are studied in the static fluctuation approximation, which is an original method. This method relies on a single and controlled approximation, which permits taking correctly into account quasiparticle correlations and thereby going beyond the independent-quasiparticle model. A closed self-consistent set of equations for calculating correlation functions at finite temperature is obtained for a finite Fermi system described by the Bardeen–Cooper–Schrieffer Hamiltonian. An equation for the energy gap is found with allowance for fluctuation effects. It is shown that the phase transition to the supefluid state is smeared upon the inclusion of fluctuations.
Vortex line in spin-orbit coupled atomic Fermi gases
Işkın, Menderes
2011-01-01
PHYSICAL REVIEW A 85, 013622 (2012) Vortex line in spin-orbit coupled atomic Fermi gases M. Iskin Department of Physics, Koc¸ University, Rumelifeneri Yolu, TR-34450 Sariyer, Istanbul, Turkey (Received 1 December 2011; published 17 January 2012) It has recently been shown that the spin-orbit coupling gives rise to topologically nontrivial and thermodynamically stable gapless superfluid phases when the pseudospin populations of an atomic Fermi gas are imbalanced, with the ...
Sound Modes of a Bose-Fermi Mixture Superfluid at Finite Temperatures
Ono, Yosuke; Sakamoto, Ryohei; Mori, Hiroyuki; Arahata, Emiko
2016-06-01
We study the sound modes of a Bose-Fermi mixture superfluid at finite temperatures in the collisional hydrodynamic regime. We extend Landau's hydrodynamic theory to deal with a Bose-Fermi mixture superfluid and show the existence of three sound modes. We calculate the hydrodynamic sound velocities numerically using the Nozières and Schmitt-Rink theory at unitarity. The three-sound-modes hybrid in Bose-Fermi mixture superfluids contrasts with the two sound modes exhibited by 3He and 4He superfluids.
Collective modes and superflow instabilities of strongly correlated Fermi superfluids
International Nuclear Information System (INIS)
We study the superfluid phase of the one-band attractive Hubbard model of fermions as a prototype of a strongly correlated s-wave fermion superfluid on a lattice. We show that the collective mode spectrum of this superfluid exhibits, in addition to the long wavelength sound mode, a sharp roton mode over a wide range of densities and interaction strengths. We compute the sound velocity and the roton gap within a generalized random phase approximation (GRPA) and show that the GRPA results are in good agreement, at strong coupling, with a spin-wave analysis of the appropriate strong-coupling pseudospin model. We also investigate, using this two-pronged approach, the breakdown of superfluidity in the presence of a supercurrent. We find that the superflow can break down at a critical flow momentum via several distinct mechanisms--depairing, Landau instabilities or dynamical instabilities--depending on the dimension, the interaction strength and the fermion density. The most interesting of these instabilities is a charge modulation dynamical instability which is distinct from previously studied dynamical instabilities of Bose superfluids. The charge order associated with this instability can be of two types: (i) a commensurate checkerboard modulation driven by softening of the roton mode at the Brillouin zone corner, or, (ii) an incommensurate density modulation arising from superflow-induced finite momentum pairing of Bogoliubov quasiparticles. We elucidate the dynamical phase diagram showing the critical flow momentum of the leading instability over a wide range of fermion densities and interaction strengths and point out implications of our results for experiments on cold atom fermion superfluids in an optical lattice.
A new superfluid phase in atomic nuclei
International Nuclear Information System (INIS)
The influence of pairing and the dynamical α-type correlations on the structure of nuclear states is studied within the enlarged superfluid model (ESM). A comparison between ESM and different modern nuclear structure models such as: the quasiparticle-phonon nuclear model, interaction boson model, Hartree-Fock-Bogoliubov, temperature dependent Hartree-Fock-Bogoliubov and Migdal's finite Fermi system model, is done for particular cases. New gap equations are obtained. The phase structure is enriched by a new superfluid phase - the so-called α-like superfluid phase-dominated by α-type correlations. New first and second order phase transitions are predicted. A first order phase transition between the α-like superfluid phase and the pairing superfluid phase seems to be observed in Sm region. New types of isomers, the so-called ''superfluid isomers'', with their bands of elementary excitations are predicted. One of them is observed in 152Sm. These isomers correspond to a second (local) minimum of the correlation energy versus pairing deformations, analogous to the fission or superdeformed (shape) isomers, which correspond to the second (local) minimum of the potential energy along the elongation degree of shape deformation. The superfluidities of neutron and proton systems in heavy nuclei region may be generated by one another. This fact leads to the explanation of the origin of the odd-even staggering of the charge radii of chains of isotopes of different nuclei. The fact that the magnitude of the α-decay reduced widths (γ2) of the neutron-defficient Pb isotopes is almost equal to the γ2 of the actinide α-decaying nuclei is due to the above mentioned induction of the neutron superfluidity into the proton system also. Such exotic data ESM can explain especially in the region of single magic nuclei. Within ESM we could find a natural microscopic description of the scissors mode that dominates the structure of the Kπ=1+ magnetic states. (author). 89 refs, 27 figs
Transport and magnetic resonance in normal and superfluid Fermi liquids
International Nuclear Information System (INIS)
This thesis provides a framework for a series of 19 papers published by the author in a study of transport and magnetic resonance in normal and superfluid Fermi liquids. The Boltzmann equation and methods for its solution are discussed. Electron-electron scattering in metals, with particular emphasis on alkali metals, is considered. Transport in a normal uncharged Fermi liquid such as pure 3He at temperatures well below its degeneracy temperature of approximately 1 K or mixtures of 3He in 4He with degeneracy temperatures ranging typically from 100 to 200 mk is discussed with emphasis on comparison with experiments with the aim of testing models of the particle-particle scattering amplitude. Transport and magnetic resonance in superfluid 3He is considered. The phenomenological treatment of relaxation is reviewed and the magnitude of the phenomenlogical relaxation time close to Tsub(c) is derived for the case of longitudinal resonance. Comments are made on non-linear magnetic resonance and textures and spin waves. (B.R.H.)
Ku, Mark J H; Mukherjee, Biswaroop; Yefsah, Tarik; Zwierlein, Martin W
2016-01-29
We follow the time evolution of a superfluid Fermi gas of resonantly interacting ^{6}Li atoms after a phase imprint. Via tomographic imaging, we observe the formation of a planar dark soliton, its subsequent snaking, and its decay into a vortex ring, which, in turn, breaks to finally leave behind a single solitonic vortex. In intermediate stages, we find evidence for an exotic structure resembling the Φ soliton, a combination of a vortex ring and a vortex line. Direct imaging of the nodal surface reveals its undulation dynamics and its decay via the puncture of the initial soliton plane. The observed evolution of the nodal surface represents dynamics beyond superfluid hydrodynamics, calling for a microscopic description of unitary fermionic superfluids out of equilibrium. PMID:26871342
Ku, Mark J. H.; Mukherjee, Biswaroop; Yefsah, Tarik; Zwierlein, Martin W.
2016-01-01
We follow the time evolution of a superfluid Fermi gas of resonantly interacting 6 atoms after a phase imprint. Via tomographic imaging, we observe the formation of a planar dark soliton, its subsequent snaking, and its decay into a vortex ring, which, in turn, breaks to finally leave behind a single solitonic vortex. In intermediate stages, we find evidence for an exotic structure resembling the Φ soliton, a combination of a vortex ring and a vortex line. Direct imaging of the nodal surface reveals its undulation dynamics and its decay via the puncture of the initial soliton plane. The observed evolution of the nodal surface represents dynamics beyond superfluid hydrodynamics, calling for a microscopic description of unitary fermionic superfluids out of equilibrium.
Faraday instability and Faraday patterns in a superfluid Fermi gas
Tang, Rong-An; Li, Hao-Cai; Xue, Ju-Kui
2011-06-01
With the consideration of the coupling between the transverse width and the longitudinal density, the parametric excitations related to Faraday waves in a cigar-shaped superfluid Fermi gas are studied. A Mathieu equation is obtained, and it is demonstrated firstly that the excited actual 3D Faraday pattern is the combination of the longitudinal Faraday density wave and the corresponding transverse width fluctuation in the longitudinal direction. The Faraday instability growth index and the kinematic equations of the Faraday density wave and the width fluctuation along the Bose-Einstein condensate (BEC)-Bardeen-Cooper-Schrieffer (BCS) crossover are also given for the first time. It is found that the 3D Faraday pattern presents quite different behaviours (such as the excitations and the motions) when the system crosses from the BEC side to the BCS side. The coupling not only plays an important role in the parametric excitation, but also determines the dominant wavelength of the spatial structure. Along the crossover, the coupling effects are more significant in the BCS side. The final numerical investigation verifies these results and gives a detailed study of the parametric excitations (i.e. Faraday instability) and the 3D pattern formation.
Faraday instability and Faraday patterns in a superfluid Fermi gas
Energy Technology Data Exchange (ETDEWEB)
Tang Rongan; Xue Jukui [Key Laboratory of Atomic Molecular Physics and Functional Materials of Gansu Province, College of Physics and Electronic Engineering, Northwest Normal University, Lanzhou, 730070 (China); Li Haocai, E-mail: tangra79@163.com, E-mail: xuejk@nwnu.edu.cn [High School Attached to Northwest Normal University, Lanzhou 730070 (China)
2011-06-14
With the consideration of the coupling between the transverse width and the longitudinal density, the parametric excitations related to Faraday waves in a cigar-shaped superfluid Fermi gas are studied. A Mathieu equation is obtained, and it is demonstrated firstly that the excited actual 3D Faraday pattern is the combination of the longitudinal Faraday density wave and the corresponding transverse width fluctuation in the longitudinal direction. The Faraday instability growth index and the kinematic equations of the Faraday density wave and the width fluctuation along the Bose-Einstein condensate (BEC)-Bardeen-Cooper-Schrieffer (BCS) crossover are also given for the first time. It is found that the 3D Faraday pattern presents quite different behaviours (such as the excitations and the motions) when the system crosses from the BEC side to the BCS side. The coupling not only plays an important role in the parametric excitation, but also determines the dominant wavelength of the spatial structure. Along the crossover, the coupling effects are more significant in the BCS side. The final numerical investigation verifies these results and gives a detailed study of the parametric excitations (i.e. Faraday instability) and the 3D pattern formation.
Dynamics of shock waves in a superfluid unitary Fermi gas
Wen, Wen; Shui, Tiankun; Shan, Yafei; Zhu, Changping
2015-09-01
We study the formation and dynamics of shock waves initiated by a repulsive potential in a superfluid unitary Fermi gas by using the order-parameter equation. In the theoretical framework, the regularization process of shock waves mediated by the quantum pressure term is purely dispersive. Our results show good agreement with the experiment of Joseph et al (2011 Phys. Rev. Lett. 106 150401). We reveal that the boxlike-shaped density peak observed in the experiment consists of many vortex rings due to the transverse instability of the dispersive shock wave. In addition, we study the transition from a sound wave to subsonic shock waves as the strength of the repulsive potential increases and show a strong qualitative change in the propagation speed of the wavefronts. For a relatively small strength of the repulsive potential, the propagation speed decreases below the sound speed with the increase of the strength as a scaling behavior. For a large strength where the shock waves are formed by colliding two spatially separated clouds, the speed is still smaller than the sound speed, but remains almost unchanged as the strength increases, which can be interpreted as the same expansion speed of the proliferation of the vortex rings originated from the transverse instability.
Transport equations and linear response of superfluid Fermi mixtures in neutron stars
Gusakov, M E
2010-01-01
We study transport properties of a strongly interacting superfluid mixture of two Fermi-liquids. A typical example of such matter is the neutron-proton liquid in the cores of neutron stars. To describe the mixture, we employ the Landau theory of Fermi-liquids, generalized to allow for the effects of superfluidity. We formulate the kinetic equation and analyze linear response of the system to vector (e.g., electromagnetic) perturbation. In particular, we calculate the transverse and longitudinal polarization functions for both liquid components. We demonstrate, that they can be expressed through the Landau parameters of the mixture and polarization functions of noninteracting matter (when the Landau quasiparticle interaction is neglected). Our results can be used, e.g., for studies of the kinetic coefficients and low-frequency long-wavelength collective modes in superfluid Fermi-mixtures.
Two-Element Mixture of Bose and Fermi Superfluids
Roy, Richard; Bowler, Ryan; Gupta, Subhadeep
2016-01-01
We report on the production of a mixture of bosonic and fermionic superfluids composed of the elements $^{174}$Yb and $^6$Li which feature strong mismatch in mass and distinct electronic properties. Simultaneous superfluidity and prolonged co-existence are confirmed through observation of the condensed fraction of bosonic and fermionic components. We demonstrate elastic coupling between the superfluids by observing the shift in dipole oscillation frequency of the bosonic component due to the presence of the fermions. The measured magnitude of the shift is consistent with a mean-field model and its direction determines the previously unknown sign of the interspecies scattering length to be positive. We also observe the exchange of angular momentum between the superfluids from the excitation of a scissors mode in the bosonic component through interspecies interactions.
Nonzero orbital angular momentum superfluidity in ultracold Fermi gases
Iskin, M.; de Melo, C. A. R. Sá
2006-01-01
We analyze the evolution of superfluidity for nonzero orbital angular momentum channels from the Bardeen-Cooper-Schrieffer (BCS) to the Bose-Einstein condensation (BEC) limit in three dimensions. First, we analyze the low energy scattering properties of finite range interactions for all possible angular momentum channels. Second, we discuss ground state ($T = 0$) superfluid properties including the order parameter, chemical potential, quasiparticle excitation spectrum, momentum distribution, ...
Coordinate-Space Hartree-Fock-Bogoliubov Solvers for Superfluid Fermi Systems in Large Boxes
Pei, J C; Harrison, R J; Nazarewicz, W; Hill, J; Galindo, D; Jia, J
2012-01-01
The self-consistent Hartree-Fock-Bogoliubov problem in large boxes can be solved accurately in the coordinate space with the recently developed solvers HFB-AX (2D) and MADNESS-HFB (3D). This is essential for the description of superfluid Fermi systems with complicated topologies and significant spatial extend, such as fissioning nuclei, weakly-bound nuclei, nuclear matter in the neutron star rust, and ultracold Fermi atoms in elongated traps. The HFB-AX solver based on B-spline techniques uses a hybrid MPI and OpenMP programming model for parallel computation for distributed parallel computation, within a node multi-threaded LAPACK and BLAS libraries are used to further enable parallel calculations of large eigensystems. The MADNESS-HFB solver uses a novel multi-resolution analysis based adaptive pseudo-spectral techniques to enable fully parallel 3D calculations of very large systems. In this work we present benchmark results for HFB-AX and MADNESS-HFB on ultracold trapped fermions.
Faraday waves in quasi-one-dimensional superfluid Fermi-Bose mixtures
DEFF Research Database (Denmark)
Abdullaev, F. Kh.; Ögren, Magnus; Sørensen, Mads Peter
2013-01-01
The generation of Faraday waves in superfluid Fermi-Bose mixtures in elongated traps is investigated. The generation of waves is achieved by periodically changing a parameter of the system in time. Two types of modulations of parameters are considered: a variation of the fermion-boson scattering...
High-Temperature Atomic Superfluidity in Lattice Boson-Fermion Mixtures
Illuminati, F.; Albus, A
2003-01-01
We consider atomic Bose-Fermi mixtures in optical lattices and study the superfluidity of fermionic atoms due to s-wave pairing induced by boson-fermion interactions. We prove that the induced fermion-fermion coupling is always {\\it attractive} if the boson-boson on site interaction is repulsive, and predict the existence of an enhanced BEC--BCS crossover as the strength of the lattice potential is varied. We show that for direct on-site fermion-fermion {\\it repulsion}, the induced attraction...
Critical temperature of the superfluid transition in Fermi-system at an arbitrary pair potential
Poluektov, Yu. M.; Soroka, A. A.
2014-01-01
A method for calculation of the critical temperature of transition of a many-particle Fermi system into a superfluid or a superconducting state at an arbitrary pair potential of the interparticle interaction is proposed. An original homogeneous integral equation, that determines the critical temperature, is transformed into a homogeneous integral equation with a symmetric kernel that enables application of a general theory of integral equations for calculation. Examples are given of calculati...
Vortex line of spin-orbit coupled Fermi superfluid through BCS to BEC Crossover
Yao, Juan; Zhang, Shizhong
Superfluid Fermi gases with spin-orbit interaction provides a unique opportunity to investigate possible effects of strong interaction in a topological superfluid. It has been suggested that with addition of Rashba-type spin-orbit coupling, a two-component Fermi gas with strong s-wave interaction can become a topological superfluid with zero-energy bound state at the core of the vortex. In this talk, I discuss the evolution of vortex structure in a spin-orbit coupled Fermi gas through the BCS-BEC crossover within Bogoliubov-de Genne formalism. We find that the largest critical current occurs in the BEC side of the resonance, in contradiction to the usual crossover without spin-orbit coupling where it occurs at unitarity. Furthermore, we discuss the core structure of the vortex by calculating the spin and density distribution around the vortex. Department of Physics and Centre of Theoretical and Computational Physics, The University of Hong Kong, Hong Kong, China.
International Nuclear Information System (INIS)
The paper reviews the understanding of superfluid helium with regard to its use as coolant for superconducting devices. The topics to be addressed include heat transfer properties of the stagnant fluid, cooling by forced flow superfluid helium, design principles for superfluid helium cryogenic systems and, finally, an illustration of these principles by a few practical examples. 18 refs
Metastable Superfluidity of Repulsive Fermionic Atoms in Optical Lattices
International Nuclear Information System (INIS)
In the fermionic Hubbard model, doubly occupied states have an exponentially large lifetime for strong repulsive interactions U. We show that this property can be used to prepare a metastable s-wave superfluid state for fermionic atoms in optical lattices described by a large-U Hubbard model. When an initial band-insulating state is expanded, the doubly occupied sites Bose condense. A mapping to the ferromagnetic Heisenberg model in an external field allows for a reliable solution of the problem. Nearest-neighbor repulsion and pair hopping are important in stabilizing superfluidity
Propagation of sound and supersonic bright solitons in superfluid Fermi gases in BCS-BEC crossover
Wen, Wen; Shen, Shun-Qing; Huang, Guoxiang
2010-01-01
We investigate the linear and nonlinear sound propagations in a cigar-shaped superfluid Fermi gas with a large particle number. We first solve analytically the eigenvalue problem of linear collective excitations and provide explicit expressions of all eigenvalues and eigenfunctions, which are valid for all superfluid regimes in the Bardeen-Cooper-Schrieffer-Bose-Einstein condensation (BCS-BEC) crossover. The linear sound speed obtained agrees well with that of a recent experimental measurement. We then consider a weak nonlinear excitation and show that the time evolution of the excitation obeys a Korteweg de Vries equation. Different from the result obtained in quasi-one-dimensional case studied previously, where subsonic dark solitons are obtained via the balance between quantum pressure and nonlinear effect, we demonstrate that bright solitons with supersonic propagating velocity can be generated in the present three-dimensional system through the balance between a waveguidelike dispersion and the interparticle interaction. The supersonic bright solitons obtained display different physical properties in different superfluid regimes and hence can be used to characterize superfluid features of the BCS-BEC crossover.
Finite-temperature quantum fluctuations in two-dimensional Fermi superfluids
Bighin, G.; Salasnich, L.
2016-01-01
In two-dimensional systems with a continuous symmetry, the Mermin-Wagner-Hohenberg theorem precludes spontaneous symmetry breaking and condensation at finite temperature. The Berezinskii-Kosterlitz-Thouless critical temperature marks the transition from a superfluid phase characterized by quasicondensation and algebraic long-range order, to a normal phase in which vortex proliferation completely destroys superfluidity. As opposed to conventional off-diagonal long-range order typical of three-dimensional superfluid systems, algebraic long-range order is driven by quantum and thermal fluctuations strongly enhanced in reduced dimensionality. Motivated by this unique scenario and by the very recent experimental realization of trapped quasi-two-dimensional fermionic clouds, we include one-loop Gaussian fluctuations in the theoretical description of resonant Fermi superfluids in two dimensions demonstrating that first sound, second sound, and also critical temperature are strongly renormalized, away from their mean-field values. In particular, we prove that in the intermediate- and strong-coupling regimes, these quantities are radically different when Gaussian fluctuations are taken into account. Our one-loop theory shows good agreement with very recent experimental data on the Berezinskii-Kosterlitz-Thouless critical temperature [Phys. Rev. Lett. 115, 010401 (2015)], 10.1103/PhysRevLett.115.010401 and on the first sound velocity, giving predictions for the second sound as a function of interaction strength and temperature that are open for experimental verification.
Induced p-wave Superfluidity in Imbalanced Fermi Gases in a Synthetic Gauge Field
Caldas, Heron; Continentino, Mucio
2015-03-01
We study pairing formation and the appearance of induced spin-triplet p-wave superfluidity in dilute three-dimensional imbalanced Fermi gases in the presence of a uniform non-Abelian gauge field. This gauge field generates a synthetic Rashba-type spin-orbit interaction which has remarkable consequences in the induced p-wave pairing gaps. Without the synthetic gauge field, the p-wave pairing occurs in one of the components due to the induced (second-order) interaction via an exchange of density fluctuations in the other component. We show that this p-wave superfluid gap induced by density fluctuations is greatly enhanced due to the Rashba-type spin-orbit coupling. This work was partially supported by CAPES, CNPq, FAPERJ, and FAPEMIG (Brazilian Agencies).
Action for anomaly in Fermi superfluids: Quantized vortices and gap nodes
International Nuclear Information System (INIS)
A general expression for the topological Novikov-Wess-Zumino (NWZ) term in the hydrodynamic action of Fermi superfluids is derived. It can be applied both to systems with gap nodes in momentum space, such as superfluid 3He-A, and to conventional superconductors with quantized vortices. The action is expressed in terms of the volume of the 6-dimensional phase space bar k, bar r enclosed by the multidimensional vortex sheet swept by Green's function singularities. While in superfluid 3He-A this action describes the chiral anomaly in 3+1 dimensions, which results from the gap nodes, in the case of vortices the NWZ term results from the spectral flow along the anomalous branches of the fermions, localized in the vortex core. At low temperatures the flow of states through E=0 determines the parameter D' characterizing the reactive force between the vortex and the system of normal fermions (heat bath). This reversible momentum exchange between the coherent condensate motion in three dimensions and the 1-dimensional motion of localized fermions is equivalent to the Callan-Harvey process of anomaly cancellation. The number of the anomalous branches of fermionic zero modes on vortices is related to the vortex winding number. 30 refs
Directory of Open Access Journals (Sweden)
S Nasirimoghadam
2011-09-01
Full Text Available The ultracold atoms fermion gas such as 6Li undergo superfluidity state. The transport quantities of these fluids have a direct dependence on the transition probabilities. Here, by obtaining possible processes in p-wave superfluid, we have shown that only binary processes are dominate at low temperatures.
Bogoliubov approach to superfluidity of atoms in an optical lattice
International Nuclear Information System (INIS)
We use the Bogoliubov theory of atoms in an optical lattice to study the approach to the Mott-insulator transition. We derive an explicit expression for the superfluid density based on the rigidity of the system under phase variations. This enables us to explore the connection between the quantum depletion of the condensate and the quasi-momentum distribution on the one hand and the superfluid fraction on the other. The approach to the insulator phase may be characterized through the filling of the band by quantum depletion, which should be directly observable via the matter-wave interference patterns. We complement these findings by self-consistent Hartree-Fock-Bogoliubov-Popov calculations for one-dimensional lattices, including the effects of a parabolic trapping potential
Inelastic scattering of xenon atoms by quantized vortices in superfluids
Pshenichnyuk, I A
2016-01-01
We study inelastic interactions of particles with quantized vortices in superfluids by using a semi-classical matter wave theory that is analogous to the Landau two-fluid equations, but allows for the vortex dynamics. The research is motivated by recent experiments on xenon doped helium nanodroplets that show clustering of the impurities along the vortex cores. We numerically simulate the dynamics of trapping and interactions of xenon atoms by quantized vortices in superfluid helium and the obtained results can be extended to scattering of other impurities by quantized vortices. Different energies and impact parameters of incident particles are considered. We show that inelastic scattering is closely linked to the generation of Kelvin waves along a quantized vortex during the interaction even if there is no capture. The capture criterion of an impurity is formulated in terms of the binding energy.
Dynamics of atom-atom correlations in the Fermi problem
Borrelli, Massimo; Sabín, Carlos; Adesso, Gerardo; Plastina, Francesco; Maniscalco, Sabrina
2012-01-01
We present a detailed perturbative study of the dynamics of several types of atom-atom correlations in the famous Fermi problem. This is an archetypal model to study micro-causality in the quantum domain, where two atoms, one initially excited and the other prepared in its ground state, interact with the vacuum electromagnetic field. The excitation can be transferred to the second atom via a flying photon, and various kinds of quantum correlations between the two are generated during this pro...
Tajima, Hiroyuki; Hanai, Ryo; Ohashi, Yoji
2016-01-01
We theoretically investigate the uniform spin susceptibility χ in the superfluid phase of an ultracold Fermi gas in the region of the Bardeen-Cooper-Schrieffer-Bose-Einstein-condensate (BCS-BEC) crossover. In our previous paper [H. Tajima et al., Phys. Rev. A 89, 033617 (2014), 10.1103/PhysRevA.89.033617], including pairing fluctuations within an extended T -matrix approximation (ETMA), we showed that strong pairing fluctuations cause the so-called spin-gap phenomenon, where χ is anomalously suppressed even in the normal state near the superfluid phase transition temperature Tc. In this paper, we extend this work to the superfluid phase below Tc, to clarify how this many-body phenomenon is affected by the superfluid order. From the comparison of the ETMA χ with the Yosida function describing the spin susceptibility in a weak-coupling BCS superfluid, we identify the region where pairing fluctuations crucially affect this magnetic quantity below Tc in the phase diagram with respect to the strength of a pairing interaction and the temperature. This spin-gap regime is found to be consistent with the previous pseudogap regime determined from the pseudogapped density of states. We also compare our results with a recent experiment on a 6Li Fermi gas. Since the spin susceptibility is sensitive to the formation of spin-singlet preformed pairs, our results would be useful for the study of pseudogap physics in an ultracold Fermi gas on the viewpoint of the spin degrees of freedom.
Adhikari, S. K.; Lu, Hong; Pu, Han
2009-12-01
We derive a generalized Gross-Pitaevskii density-functional equation appropriate to study the Bose-Einstein condensate (BEC) of dimers formed of singlet spin-half Fermi pairs in the BEC-unitarity crossover while the dimer-dimer scattering length a changes from 0 to ∞ . Using an effective one-dimensional form of this equation, we study the phenomenon of dynamical self-trapping of a cigar-shaped Fermi superfluid in the entire BEC-unitarity crossover in a double-well potential. A simple two-mode model is constructed to provide analytical insights. We also discuss the consequence of our study on the self-trapping of an atomic BEC in a double-well potential.
Quantized vortices in superfluid helium and atomic Bose-Einstein condensates
Tsubota, Makoto; Kasamatsu, Kenichi; Kobayashi, Michikazu
2010-01-01
This article reviews recent developments in the physics of quantized vortices in superfluid helium and atomic Bose-Einstein condensates. Quantized vortices appear in low-temperature quantum condensed systems as the direct product of Bose-Einstein condensation. Quantized vortices were first discovered in superfluid 4He in the 1950s, and have since been studied with a primary focus on the quantum hydrodynamics of this system. Since the discovery of superfluid 3He in 1972, quantized vortices cha...
Institute of Scientific and Technical Information of China (English)
Dong Hang; Ma Yong-Li
2009-01-01
Using quantum hydrodynamic approaches, we study the quantum pressure correction to the collective excitation spectrum of the interacting trapped superfluid Fermi gases in the BEC-BCS crossover. Based on a phenomenological equation of state, we derive hydrodynamic equations of the system in the whole BEC-BCS crossover regime. Beyond the Thomas-Fermi approximation, expressions of the frequency corrections of collective modes for both spherical and axial symmetric traps excited in the BEC-BCS crossover are given explicitly. The corrections of the eigenfrequencies due to the quantum pressure and their dependence on the inverse interaction strength. Anisotropic parameter and particle numbers of the condensate are discussed in detail.
Probing superfluid properties in strongly correlated Fermi gases with high spatial resolution
Energy Technology Data Exchange (ETDEWEB)
Weimer, Wolf
2014-07-01
In this thesis an apparatus to study ultracold fermionic {sup 6}Li with tunable interaction strength and dimensionality is presented. The apparatus is applied to investigate the speed of sound v{sub s} and the superfluid critical velocity v{sub c} across the transition from Bose-Einstein condensation (BEC) to Bardeen-Cooper-Schrieffer (BCS) superfluidity. The results set benchmarks for theories describing strongly correlated systems. To measure v{sub c}, an obstacle, that is formed by a tightly focused laser beam, is moved through a superfluid sample with a constant velocity along a line of constant density. For velocities larger than v{sub c} heating of the gas is observed. The critical velocity is mapped out for various different interaction strengths covering the BEC-BCS crossover. According to the Landau criterion and Bogolyubov theory, v{sub c} should be closely related to v{sub s} in a Bose-Einstein condensate. The measurement of v{sub s} is conducted by creating a density modulation in the centre of the cloud and tracking the excited modulation. The velocities v{sub s} and v{sub c} are measured in a similar range of interaction strengths and in similar samples to ensure comparability. The apparatus which provides the ultracold samples is a two chamber design with a magneto-optical trap that is loaded via a Zeeman slower. The subsequent cooling steps are all-optical and finally create an ultracold oblate atom cloud inside a flat vacuum cell. This cell provides optimal optical access and is placed between two high numerical aperture microscope objectives. These objectives are used to probe the samples in-situ on length scales which are comparable to the intrinsic length scales of the gases. Similarly, optical dipole potentials are employed to manipulate the clouds on the same small length scales. The oblate samples are sufficiently flat such that there spatial extent along the microscope axes is smaller than the depth of field of the objectives. With an
Expansion dynamics of Fermi atoms in optical lattice
International Nuclear Information System (INIS)
We study the non-equilibrium quantum dynamics of attractive Fermi gases in one- and two-dimensional optical lattice. We use the dynamic Bogoliubov–de Gennes (DBdG) method and time-evolving block decimation (TEBD) to investigate the expansion dynamics, which can be implemented by suddenly removing the harmonic trap. The evolutions of density and superfluid order parameters have been calculated. We find that for the noninteracting case, the expansion rate is linear with hopping amplitude, which is a ballistic expansion result. And the interaction damps the expansion rate exponentially both in one and two dimensions and makes it deviate from the ballistic expansion. - Highlights: • We use DBdG method and TEBD to investigate the expansion dynamics in optical lattice. • We calculate the evolution of density and superfluid order parameters. • We find a ballistic expansion result for non-interacting case. • We find interaction damps the expansion rate exponentially
Atom scattering off superfluid 4He clusters and films
International Nuclear Information System (INIS)
In this work, the HNC-Euler-Lagrange theory is applied to the many-body scattering problem. We use time-dependent variational correlated wave functions in excitation calculations in order to describe atom scattering off nanoclusters and microscopically thin films of superfluid helium-4. Apart from elastic processes, the level of implementation of the method includes dissipation, i.e. processes in which the atom imparts energy to the cluster/film, such as direct inelastic scattering and sticking. From the cross sections/probabilities for elastic and dissipative processes, information about the energetic structure (excitation energies, dispersion relations) of the helium-4 system can be gleaned, and, for scattering off a helium-4 film, about the strength of Van der Waal forces between atom and the substrate, on which the film is adsorbed. For the determination of inelastic scattering cross sections, we develop a method based on the expansion of the expectation value of the probability current to second order in correlation fluctuations which leads to a formulation which allows to identify the decay probability into open scattering channels. Various differential cross sections are calculated such as the probability for energy- and momentum-transfer to the helium cluster which is the analogon to the dynamic structure function measured by inelastic neutron scattering and which allows the determination of the surface wave (ripplons) dispersion relation. The effect of particle statistics on identical particle scattering is studied by comparing helium-4 scattering to impurity (helium-3) scattering off helium-4 clusters; e.g. we show how the elastic conversion process from helium-4 atom to roton and back can be understood as a resonance phenomenon at the excitation energy of the roton in helium clusters. The connection between resonances in the elastic scattering channel to their counterpart in inelastic channels is highlighted in the example of our results for quantum
Atom scattering off superfluid4He clusters and films
International Nuclear Information System (INIS)
In this work, the HNC-Euler-Lagrange theory is applied to the many-body scattering problem. We use time-dependent variational correlated wave functions in excitation calculations in order to describe atom scattering off nanoclusters and microscopically thin films of superfluid helium-4. Apart from elastic processes, the level of implementation of the method includes dissipation, i.e. processes in which the atom imparts energy to the cluster/film, such as direct inelastic scattering and sticking. From the cross sections/probabilities for elastic and dissipative processes, information about the energetic structure (excitation energies, dispersion relations) of the helium-4 system can be gleaned, and, for scattering off a helium-4 film, about the strength of Van der Waal forces between atom and the substrate, on which the film is adsorbed. For the determination of inelastic scattering cross sections, we develop a method based on the expansion of the expectation value of the probability current to second order in correlation fluctuations which leads to a formulation which allows to identify the decay probability into open scattering channels. Various differential cross sections are calculated such as the probability for energy- and momentum-transfer to the helium cluster which is the analogon to the dynamic structure function measured by inelastic neutron scattering and which allows the determination of the surface wave (ripplons) dispersion relation. The effect of particle statistics on identical particle scattering is studied by comparing helium-4 scattering to impurity (helium-3) scattering off helium-4 clusters; e.g. we show how the elastic conversion process from helium-4 atom to roton and back can be understood as a resonance phenomenon at the excitation energy of the roton in helium clusters. The connection between resonances in the elastic scattering channel to their counterpart in inelastic channels is highlighted in the example of our results for quantum
Pal, Arijeet; Huse, David
2012-02-01
Phase separation between paired superfluid and partially polarized normal phases has been observed by various experimental groups around the world using resonantly-interacting spin-imbalanced, hyperfine states of fermionic atoms. In this work we phenomenologically study the effect of the evaporation of atoms and explore the possibility of realizing a non-equilibrium steady state with chemical potential and temperature gradients in some of these experiments.
Mean field dynamics of superfluid-insulator phase transition in a gas of ultra cold atoms
Zakrzewski, Jakub
2004-01-01
A large scale dynamical simulation of the superfluid to Mott insulator transition in the gas of ultra cold atoms placed in an optical lattice is performed using the time dependent Gutzwiller mean field approach. This approximate treatment allows us to take into account most of the details of the recent experiment [Nature 415, 39 (2002)] where by changing the depth of the lattice potential an adiabatic transition from a superfluid to a Mott insulator state has been reported. Our simulations re...
Lattice simulation of ultracold atomic Bose-Fermi mixtures
Yamamoto, Arata
2012-01-01
Bose-Fermi mixtures have been recently realized and invesitigated in ultracold atomic experiments. We formulate quantum Monte Carlo simulation of Bose-Fermi mixtures on the (3+1)-dimensional lattice. As its first application, we analyze the boson-fermion pair correlation and the phase diagram of the Bose-Einstein condensation.
Degenerate atom-molecule mixture in a cold Fermi gas
International Nuclear Information System (INIS)
We show that the atom-molecule mixture formed in a degenerate atomic Fermi gas with interspecies repulsion near a Feshbach resonance constitutes a peculiar system where the atomic component is almost nondegenerate but quantum degeneracy of molecules is important. We develop a thermodynamic approach for studying this mixture, explain experimental observations, and predict optimal conditions for achieving molecular Bose-Einstein condensation
Degenerate Atom-Molecule Mixture in a Cold Fermi Gas
Kokkelmans, S.J.J.M.F.; Shlyapnikov, G. V.; Salomon, R.
2004-01-01
We show that the atom-molecule mixture formed in a degenerate atomic Fermi gas with interspecies repulsion near a Feshbach resonance, constitutes a peculiar system where the atomic component is almost non-degenerate but quantum degeneracy of molecules is important. We develop a thermodynamic approach for studying this mixture, explain experimental observations and predict optimal conditions for achieving molecular BEC.
Theory of dark matter superfluidity
Berezhiani, Lasha; Khoury, Justin
2015-11-01
We propose a novel theory of dark matter (DM) superfluidity that matches the successes of the Λ cold dark matter (Λ CDM ) model on cosmological scales while simultaneously reproducing the modified Newtonian dynamics (MOND) phenomenology on galactic scales. The DM and MOND components have a common origin, representing different phases of a single underlying substance. DM consists of axionlike particles with mass of order eV and strong self-interactions. The condensate has a polytropic equation of state P ˜ρ3 giving rise to a superfluid core within galaxies. Instead of behaving as individual collisionless particles, the DM superfluid is more aptly described as collective excitations. Superfluid phonons, in particular, are assumed to be governed by a MOND-like effective action and mediate a MONDian acceleration between baryonic matter particles. Our framework naturally distinguishes between galaxies (where MOND is successful) and galaxy clusters (where MOND is not); due to the higher velocity dispersion in clusters, and correspondingly higher temperature, the DM in clusters is either in a mixture of superfluid and the normal phase or fully in the normal phase. The rich and well-studied physics of superfluidity leads to a number of observational signatures: an array of low-density vortices in galaxies; merger dynamics that depend on the infall velocity vs phonon sound speed; distinct mass peaks in bulletlike cluster mergers, corresponding to superfluid and normal components; and interference patters in supercritical mergers. Remarkably, the superfluid phonon effective theory is strikingly similar to that of the unitary Fermi gas, which has attracted much excitement in the cold atom community in recent years. The critical temperature for DM superfluidity is of order mK, comparable to known cold atom Bose-Einstein condensates. Identifying a precise cold atom analog would give important insights on the microphysical interactions underlying DM superfluidity
Maria Goeppert Mayer Prize Talk: Superfluid Atom Circuits
Campbell, Gretchen
2016-05-01
We have performed a series of experiments with ring-shaped Bose-Einstein Condensates, with and without the addition of a ``weak link'' barrier. Weak connections between superconductors or superfluids can differ from classical links due to quantum coherence, which allows for flow without resistance. The properties of a weak link are characterized by a single function, the current-phase relationship. In recent experiments, we have developed a technique to directly measure the current-phase relationship of the weak link. The weak link is created using a laser beam that acts as a barrier across one side of the ring condensate. By rotating the barrier, we can control the current around the ring. When the weak link is rotated at at low rotation rates, we observe phase slips between well-defined, quantized current states, and have demonstrated that the system exhibits hysteresis. At higher rotation rates we have directly measured the onset of resistive flow across the weak link. Such measurements may open new avenues of research in quantum transport. More recently, we have studied the behavior of the ring BEC when the radius is expanded at supersonic rates. Because information can propagate only at the speed of sound, the supersonic expansion creates causally disconnected regions, whose phases evolve at different rates. Such experiments may allow us to study cosmic inflation at laboratory scales.
Pseudospin pairing and transport in atomic Fermi gases and bilayer systems
Mink, M.P.
2012-01-01
In this Thesis we consider the behavior of the drag conductivity close to exciton condensation in bilayer systems and close to the superfluid transition in cold Fermi gases. In chapter 2 we calculate the transition temperature for exciton condensation in double-layer graphene, showing that the remot
Sanpera, A.; Kantian, A.; Sanchez-Palencia, L.; Zakrzewski, J.; Lewenstein, M.
2004-07-01
We investigate strongly interacting atomic Fermi-Bose mixtures in inhomogeneous and random optical lattices. We derive an effective Hamiltonian for the system and discuss its low temperature physics. We demonstrate the possibility of controlling the interactions at local level in inhomogeneous but regular lattices. Such a control leads to the achievement of Fermi glass, quantum Fermi spin-glass, and quantum percolation regimes involving bare and/or composite fermions in random lattices.
Inhomogeneous atomic Bose-Fermi mixtures in cubic lattices
International Nuclear Information System (INIS)
We determine the ground state properties of inhomogeneous mixtures of bosons and fermions in cubic lattices and parabolic confining potentials. For finite hopping we determine the domain boundaries between Mott-insulator plateaux and hopping-dominated regions for lattices of arbitrary dimension within mean-field and perturbation theory. The results are compared with a new numerical method that is based on a Gutzwiller variational approach for the bosons and an exact treatment for the fermions. The findings can be applied as a guideline for future experiments with trapped atomic Bose-Fermi mixtures in optical lattices
Inhomogeneous atomic Bose-Fermi mixtures in cubic lattices.
Cramer, M; Eisert, J; Illuminati, F
2004-11-01
We determine the ground state properties of inhomogeneous mixtures of bosons and fermions in cubic lattices and parabolic confining potentials. For finite hopping we determine the domain boundaries between Mott-insulator plateaux and hopping-dominated regions for lattices of arbitrary dimension within mean-field and perturbation theory. The results are compared with a new numerical method that is based on a Gutzwiller variational approach for the bosons and an exact treatment for the fermions. The findings can be applied as a guideline for future experiments with trapped atomic Bose-Fermi mixtures in optical lattices. PMID:15600816
Measurement of the hyperfine splitting of {sup 133}Cs atoms in superfluid helium
Energy Technology Data Exchange (ETDEWEB)
Imamura, K., E-mail: kimamura@riken.jp [RIKEN Nishina Center (Japan); Furukawa, T. [Tokyo Metropolitan University, Department of Physics (Japan); Yang, X. F. [Peking University, School of Physics (China); Mitsuya, Y. [Meiji University, Department of Physics (Japan); Fujita, T. [Osaka University, Department of Physics (Japan); Hayasaka, M. [Tokyo Gakugei University, Department of Physics (Japan); Kobayashi, T. [RIKEN Center for Advanced Photonics (Japan); Hatakeyama, A. [Tokyo University of Agriculture and Technology, Department of Applied Physics (Japan); Ueno, H. [RIKEN Nishina Center (Japan); Odashima, H. [Meiji University, Department of Physics (Japan); Matsuo, Y. [Hosei University, Department of Advanced Sciences (Japan)
2015-04-15
We have been developing a new nuclear laser spectroscopy method named “OROCHI” (Optical RI-atom Observation in Condensed Helium as Ion-catcher). OROCHI utilizes superfluid helium (He II) not only as an efficient stopping medium of highly energetic ions but also as a host matrix of in-situ atomic laser spectroscopy. Using these characteristic of He II, we produce atomic spin polarization and measure Zeeman and hyperfine structure (HFS) splitting using laser-RF (radio frequency) / MW (microwave) double resonance method. From the measured energy splittings, we can deduce nuclear spins and moments. So far, we have conducted a series of experiments using both stable ({sup 85,87}Rb, {sup 133}Cs, {sup 197}Au, {sup 107,109}Ag) and unstable isotopes ({sup 84,86}Rb) to confirm the feasibility of OROCHI method, especially observing Zeeman resonance and determining nuclear spins. The measurement of HFS splitting of atoms introduced into He II is indispensable to clarify the nuclear properties by deducing nuclear moments as well as the study of nuclear spins. For this purpose, we perform a precision measurement of HFS of {sup 133}Cs atoms immersed in He II using laser ablation technique. In this paper, we describe the result of the experiment.
Measurement of the hyperfine splitting of 133Cs atoms in superfluid helium
International Nuclear Information System (INIS)
We have been developing a new nuclear laser spectroscopy method named “OROCHI” (Optical RI-atom Observation in Condensed Helium as Ion-catcher). OROCHI utilizes superfluid helium (He II) not only as an efficient stopping medium of highly energetic ions but also as a host matrix of in-situ atomic laser spectroscopy. Using these characteristic of He II, we produce atomic spin polarization and measure Zeeman and hyperfine structure (HFS) splitting using laser-RF (radio frequency) / MW (microwave) double resonance method. From the measured energy splittings, we can deduce nuclear spins and moments. So far, we have conducted a series of experiments using both stable (85,87Rb, 133Cs, 197Au, 107,109Ag) and unstable isotopes (84,86Rb) to confirm the feasibility of OROCHI method, especially observing Zeeman resonance and determining nuclear spins. The measurement of HFS splitting of atoms introduced into He II is indispensable to clarify the nuclear properties by deducing nuclear moments as well as the study of nuclear spins. For this purpose, we perform a precision measurement of HFS of 133Cs atoms immersed in He II using laser ablation technique. In this paper, we describe the result of the experiment
Effective mass of 4He atom in superfluid and normal phases
International Nuclear Information System (INIS)
The formula for the temperature dependence of the effective mass of a 4He atom in the superfluid and normal phases is obtained. This expression for the effective mass allows one to eliminate infra-red divergences, being applicable at all temperatures, except for a narrow fluctuation region 0.97<< approx T/Tc<=1. In the high and low temperature limits, as well as in the interactionless limit, the obtained expression reproduces the well known results. The temperature dependence of the heat capacity and the phase transition temperature Tc∼2.18 K are calculated, by using the formula obtained for the effective mass. In the framework of the approach proposed in this work, the small critical index η is determined in the random phase approximation. The obtained value corresponds to the well known result
Atom loss maximum in ultra-cold Fermi gases
International Nuclear Information System (INIS)
Recent experiments on atom loss in ultra-cold Fermi gases all show a maximum at a magnetic field below Feshbach resonance, where the s-wave scattering length is large (comparable to inter-particle distance) and positive. These experiments have been performed over a wide range of conditions, with temperatures and trap depths spanning three decades. Different groups have come up with different explanations, including the emergence of Stoner ferromagnetism. Here, we show that this maximum is a consequence of two major steps. The first is the establishment of a population of shallow dimers, which is the combined effect of dimer formation through three-body recombination, and the dissociation of shallow dimers back to atoms through collisions. The dissociation process will be temperature dependent and is affected by Pauli blocking at low temperatures. The second is the relaxation of shallow dimers into tightly bound dimers through atom-dimer and dimer-dimer collisions. In these collisions, a significant amount of energy is released. The reaction products leave the trap, leading to trap loss. We have constructed a simple set of rate equations describing these processes. Remarkably, even with only a few parameters, these equations reproduce the loss rate observed in all recent experiments, despite their widely different experimental conditions. Our studies show that the location of the maximum loss rate depends crucially on experimental parameters such as trap depth and temperature. These extrinsic characters show that this maximum is not a reliable probe of the nature of the underlying quantum states. The physics of our equations also explains some general trends found in current experiments.
Chen, Qijin
2016-01-01
BCS–Bose-Einstein condensation (BEC) crossover is effected by increasing pairing strength between fermions from weak to strong in the particle-particle channel, and has attracted a lot of attention since the experimental realization of quantum degenerate atomic Fermi gases. Here we study the effect of the (often dropped) particle-hole channel on the zero T gap Δ(0), superfluid transition temperature Tc, the pseudogap at Tc, and the mean-field ratio 2Δ(0)/, from BCS through BEC regimes, using a pairing fluctuation theory which includes self-consistently the contributions of finite-momentum pairs and features a pseudogap in single particle excitation spectrum. Summing over the infinite particle-hole ladder diagrams, we find a complex dynamical structure for the particle-hole susceptibility χph, and conclude that neglecting the self-energy feedback causes a serious over-estimate of χph. While our result in the BCS limit agrees with Gor’kov et al., the particle-hole channel effect becomes more complex and pronounced in the crossover regime, where χph is reduced by both a smaller Fermi surface and a big (pseudo)gap. Deep in the BEC regime, the particle-hole channel contributions drop to zero. We predict a density dependence of the magnetic field at the Feshbach resonance, which can be used to quantify χph and test different theories. PMID:27183875
Chen, Qijin
2016-05-01
BCS–Bose-Einstein condensation (BEC) crossover is effected by increasing pairing strength between fermions from weak to strong in the particle-particle channel, and has attracted a lot of attention since the experimental realization of quantum degenerate atomic Fermi gases. Here we study the effect of the (often dropped) particle-hole channel on the zero T gap Δ(0), superfluid transition temperature Tc, the pseudogap at Tc, and the mean-field ratio 2Δ(0)/, from BCS through BEC regimes, using a pairing fluctuation theory which includes self-consistently the contributions of finite-momentum pairs and features a pseudogap in single particle excitation spectrum. Summing over the infinite particle-hole ladder diagrams, we find a complex dynamical structure for the particle-hole susceptibility χph, and conclude that neglecting the self-energy feedback causes a serious over-estimate of χph. While our result in the BCS limit agrees with Gor’kov et al., the particle-hole channel effect becomes more complex and pronounced in the crossover regime, where χph is reduced by both a smaller Fermi surface and a big (pseudo)gap. Deep in the BEC regime, the particle-hole channel contributions drop to zero. We predict a density dependence of the magnetic field at the Feshbach resonance, which can be used to quantify χph and test different theories.
Capponi, S.; Lecheminant, P.; Totsuka, K.
2016-04-01
Alkaline-earth and ytterbium cold atomic gases make it possible to simulate SU(N)-symmetric fermionic systems in a very controlled fashion. Such a high symmetry is expected to give rise to a variety of novel phenomena ranging from molecular Luttinger liquids to (symmetry-protected) topological phases. We review some of the phases that can be stabilized in a one dimensional lattice. The physics of this multi-component Fermi gas turns out to be much richer and more exotic than in the standard SU(2) case. For N > 2, the phase diagram is quite rich already in the case of the single-band model, including a molecular Luttinger liquid (with dominant superfluid instability in the N-particle channel) for incommensurate fillings, as well as various Mott-insulating phases occurring at commensurate fillings. Particular attention will be paid to the cases with additional orbital degree of freedom (which is accessible experimentally either by taking into account two atomic states or by putting atoms in the p-band levels). We introduce two microscopic models which are relevant for these cases and discuss their symmetries and strong coupling limits. More intriguing phase diagrams are then presented including, for instance, symmetry protected topological phases characterized by non-trivial edge states.
International Nuclear Information System (INIS)
For systems of interacting, ultracold spin-zero neutral bosonic atoms, harmonically trapped and subject to an optical lattice potential, we derive an Extended Bose Hubbard (EBH) model by developing a systematic expansion for the Hamiltonian of the system in powers of the lattice parameters and of a scale parameter, the lattice attenuation factor. We identify the dominant terms that need to be retained in realistic experimental conditions, up to nearest-neighbor interactions and nearest-neighbor hoppings conditioned by the on-site occupation numbers. In the mean field approximation, we determine the free energy of the system and study the phase diagram both at zero and at finite temperature. At variance with the standard on site Bose Hubbard model, the zero-temperature phase diagram of the EBH model possesses a dual structure in the Mott insulating regime. Namely, for specific ranges of the lattice parameters, a density wave phase characterizes the system at integer fillings, with domains of alternating mean occupation numbers that are the atomic counterparts of the domains of staggered magnetizations in an antiferromagnetic phase. We show as well that in the EBH model, a zero-temperature quantum phase transition to pair superfluidity is, in principle, possible, but completely suppressed at the lowest order in the lattice attenuation factor. Finally, we determine the possible occurrence of the different phases as a function of the experimentally controllable lattice parameters
National Aeronautics and Space Administration — Fermi is a powerful space observatory that will open a wide window on the universe. Gamma rays are the highest-energy form of light, and the gamma-ray sky is...
Ferromagnetism in a repulsive atomic Fermi gas with correlated disorder
Pilati, S.; Fratini, E.
2016-05-01
We investigate the zero-temperature ferromagnetic behavior of a two-component repulsive Fermi gas in the presence of a correlated random field that represents an optical speckle pattern. The density is tuned so that the (noninteracting) Fermi energy is close to the mobility edge of the Anderson localization transition. We employ quantum Monte Carlo simulations to determine various ground-state properties, including the equation of state, the magnetic susceptibility, and the energy of an impurity immersed in a polarized Fermi gas (repulsive polaron). In the weakly interacting limit, the magnetic susceptibility is found to be suppressed by disorder. However, it rapidly increases with the interaction strength, and it diverges at a much weaker interaction strength compared to the clean gas. Both the transition from the paramagnetic phase to the partially ferromagnetic phase, and the one from the partially to the fully ferromagnetic phase, are strongly favored by disorder, indicating a case of order induced by disorder.
Probing ultracold Fermi gases with light-induced gauge potentials
International Nuclear Information System (INIS)
We theoretically investigate the response of a two-component Fermi gas to vector potentials that couple separately to the two spin components. Such vector potentials may be implemented in ultracold atomic gases using optically dressed states. Our study indicates that light-induced gauge potentials may be used to probe the properties of the interacting ultracold Fermi gas, providing, among other things, ways to measure the superfluid density and the strength of pairing.
Inhomogeneous atomic Bose-Fermi mixtures in cubic lattices
Cramer, M.; Eisert, J.; Illuminati, F.
2003-01-01
We determine the ground state properties of inhomogeneous mixtures of bosons and fermions in cubic lattices by studying the Bose-Fermi Hubbard model including parabolic confining potentials. We present the exact solution in the limit of vanishing hopping (ultradeep lattices) and study the resulting domain structure of composite particles. For finite hopping we determine the domain boundaries between Mott-insulator plateaux and hopping-dominated regions for lattices of arbitrary dimensionality...
Velocity-dependent quantum phase slips in 1D atomic superfluids
Tanzi, Luca; Scaffidi Abbate, Simona; Cataldini, Federica; Gori, Lorenzo; Lucioni, Eleonora; Inguscio, Massimo; Modugno, Giovanni; D’Errico, Chiara
2016-01-01
Quantum phase slips are the primary excitations in one-dimensional superfluids and superconductors at low temperatures but their existence in ultracold quantum gases has not been demonstrated yet. We now study experimentally the nucleation rate of phase slips in one-dimensional superfluids realized with ultracold quantum gases, flowing along a periodic potential. We observe a crossover between a regime of temperature-dependent dissipation at small velocity and interaction and a second regime of velocity-dependent dissipation at larger velocity and interaction. This behavior is consistent with the predicted crossover from thermally-assisted quantum phase slips to purely quantum phase slips. PMID:27188334
Theory of open Fermi systems for atomic nuclei
International Nuclear Information System (INIS)
Formulae for amplitudes of direct elastic and inelastic nuclear reactions with participation of nucleons and compound particles are constructed on the basis of the quantum theory of open Fermi systems by means of the projection operators method and the delay time technique. It is shown that real parts of nucleon-nuclear and nucleus-nuclear optical potentials and transfer operators for inelastic channels are determined by vacuum nucleon-nucleon potentials for the case of the global averaging scheme. It is found that real parts of global optical potentials are deep and attracting
Bose-Einstein condensation and superfluidity
Pitaevskii, Lev
2016-01-01
This volume introduces the basic concepts of Bose–Einstein condensation and superfluidity. It makes special reference to the physics of ultracold atomic gases; an area in which enormous experimental and theoretical progress has been achieved in the last twenty years. Various theoretical approaches to describing the physics of interacting bosons and of interacting Fermi gases, giving rise to bosonic pairs and hence to condensation, are discussed in detail, both in uniform and harmonically trapped configurations. Special focus is given to the comparison between theory and experiment, concerning various equilibrium, dynamic, thermodynamic, and superfluid properties of these novel systems. The volume also includes discussions of ultracold gases in dimensions, quantum mixtures, and long-range dipolar interactions.
Iskin, M.
2016-07-01
We first show that the many-body Hamiltonian governing the physical properties of an alkaline-earth 173Yb Fermi gas across the recently realized orbital Feshbach resonance is exactly analogous to that of two-band s -wave superconductors with contact interactions; i.e., even though the free-particle bands have a tunable energy offset in between and are coupled by a Josephson-type attractive interband pair scattering, the intraband interactions have exactly the same strength. We then introduce two intraband order parameters within the BCS mean-field approximation and investigate the competition between their in-phase and out-of-phase (i.e., the so-called π -phase) solutions in the entire BCS-BEC evolution at zero temperature.
Strongly interacting Fermi systems in 1/N expansion: From cold atoms to color superconductivity
Czech Academy of Sciences Publication Activity Database
Abuki, H.; Brauner, Tomáš
2008-01-01
Roč. 78, č. 12 (2008), 125010/1-125010/13. ISSN 1550-7998 R&D Projects: GA ČR GA202/06/0734 Institutional research plan: CEZ:AV0Z10480505 Keywords : BCS-BEC crossover * Unitary Fermi gas * Quark matter Subject RIV: BG - Nuclear, Atomic and Molecular Physics, Colliders Impact factor: 5.050, year: 2008
Recoil-limited laser cooling of 87Sr atoms near the Fermi temperature.
Mukaiyama, Takashi; Katori, Hidetoshi; Ido, Tetsuya; Li, Ying; Kuwata-Gonokami, Makoto
2003-03-21
A dynamic magneto-optical trap, which relies on the rapid randomization of population in Zeeman substates, has been demonstrated for fermionic strontium atoms on the 1S0-3P1 intercombination transition. The obtained sample, 1x10(6) atoms at a temperature of 2 microK in the trap, was further Doppler cooled and polarized in a far-off resonant optical lattice to achieve 2 times the Fermi temperature. PMID:12688925
A unified microscopic theory of superfluidity and superconductivity
International Nuclear Information System (INIS)
A consistent and unified microscopic theory of a novel two-stage Fermi-Bose liquid (FBL) scenarios of superfluidity and superconductivity is developed as a combined theory of Fermi- and superfluid (SF) Bose-liquid. Modified and generalized BCS like pairing theory of fermions is presented. In analogy to that a detail boson pairing theory is developed. The single particle (SPC) and pair condensation (PC) features of an attracting 3d- and 2d-Bose gas as a function of the interboson coupling constant in the complete range 0 ≤ T ≤ Tc is studied in detail. It is shown that such SPC and PC of an attracting composite bosons (Cooper pairs, bipolarons, holons, 4He atoms, deuterons, alpha particles) lies on the basis of superfluidity both in Fermi and Bose systems. It is argued that the coexistence of the order parameters of attracting fermions ΔF and bosons ΔB leads to the superfluidity and superconductivity by two FBL scenarios. One of these scenarios is realized in so-called fermion superconductors (FSC) and other -in boson one (BSC) in which the gapless superconductivity is caused by absence of the gap ΔSF in the excitation spectrum of bosons and not by presence of point or line nodes of the BCS-like gap ΔF. The new adequate determination for basic superconducting parameters of FSC and BSC are given. The necessary and sufficient microscopic criterions for a superfluidity is formulated. The theory proposed is consistent with the different experimental data available in 4He, 3He, superconductors, nucleis, neutron stars and others. (author). 133 refs, 14 figs
Fermi-Dirac gas of atoms in a box with low adiabatic invariant
International Nuclear Information System (INIS)
Quantum degenerate Fermi-Dirac gas of atoms, confined in a cubic box, shows an energy spectrum, which is discrete and strongly dependent on the atomic mass number, Aat, box geometry and temperature, for low product of Aat and the adiabatic invariant, TV1/3, i.e. on γ = AatTV1/3. The present study compares the total number of particles and the total energy obtained by summing up the contributions of a finite number of states, defined by the values of γ, to the widespread approximations of the corresponding integrals. The sums show simple calculation algorithms and more precise results for a large interval of values of γ. A new accurate analytic formula for the chemical potential of the Fermi-Dirac quantum gas is also given. (author)
Vortex properties of a resonant superfluid
International Nuclear Information System (INIS)
The properties of a vortex in a rotating superfluid Fermi gas are studied in the unitary limit. A phenomenological approach based on Ginzburg-Landau theory is developed for this purpose. The density profiles, including those of the normal fluid and superfluid, are obtained at various temperatures and rotation frequencies. The superfluid and normal fluid densities can be identified from the angular momentum density. The total free energy and angular momentum of the vortex are also obtained
Mapping the Two-Component Atomic Fermi Gas to the Nuclear Shell-Model
DEFF Research Database (Denmark)
Özen, C.; Zinner, Nikolaj Thomas
2014-01-01
the external potential becomes important. A system of two-species fermionic cold atoms with an attractive zero-range interaction is analogous to a simple model of nucleus in which neutrons and protons interact only through a residual pairing interaction. In this article, we discuss how the problem of...... a two-component atomic fermi gas in a tight external trap can be mapped to the nuclear shell model so that readily available many-body techniques in nuclear physics, such as the Shell Model Monte Carlo (SMMC) method, can be directly applied to the study of these systems. We demonstrate an...
Energy Technology Data Exchange (ETDEWEB)
Roberts, David C [Los Alamos National Laboratory
2008-01-01
The article considers the dramatic phenomenon of seemingly frictionless flow of slow-moving superfluids. Specifically the question of whether an object in a superfluid flow experiences any drag force is addressed. A brief account is given of the history of this problem and it is argued that recent advances in ultracold atomic physics can shed much new light on this problem. The article presents the commonly held notion that sufficiently slow-moving superfluids can flow without drag and also discusses research suggesting that scattering quantum fluctuations might cause drag in a superfluid moving at any speed.
Decay of a superfluid current of ultracold atoms in a toroidal trap
Mathey, Amy C.; Clark, Charles W.; Mathey, L.
2014-08-01
Using a numerical implementation of the truncated Wigner approximation, we simulate the experiment reported by Ramanathan et al. in Phys. Rev. Lett. 106, 130401 (2011), 10.1103/PhysRevLett.106.130401, in which a Bose-Einstein condensate is created in a toroidal trap and set into rotation via a phase imprinting technique. A potential barrier is then placed in the trap to study the decay of the superflow. We find that the current decays via thermally activated phase slips, which can also be visualized as vortices crossing the barrier region in the radial direction. Adopting the notion of critical velocity used in the experiment, we determine it to be lower than the local speed of sound at the barrier, in contradiction to the predictions of the zero-temperature Gross-Pitaevskii equation. We map out the superfluid decay rate and critical velocity as a function of temperature and observe a strong dependence. Thermal fluctuations offer a partial explanation of the experimentally observed reduction of the critical velocity from the phonon velocity.
Institute of Scientific and Technical Information of China (English)
XIONG De-Zhi; CHEN Hai-Xia; WANG Peng-Jun; YU Xu-Dong; GAO Feng; ZHANG Jing
2008-01-01
@@ We report on the attainment of quantum degeneracy of 40K by means of efficient thermal collisions with the evaporatively cooled 87Rb atoms.In a quadrupole-Ioffe configuration trap,potassium atoms are cooled to 0.5 times the Fermi temperature.We obtain up to 7.59 × 105 degenerate fermions 40K.
Energy Technology Data Exchange (ETDEWEB)
Fujita, T., E-mail: tomomi.fujita@riken.jp [Osaka University, Department of Physics (Japan); Furukawa, T. [Tokyo Metropolitan University, Department of Physics (Japan); Imamura, K.; Yang, X. F. [RIKEN Nishina Center (Japan); Hatakeyama, A. [Tokyo University of Agriculture and Technology, Department of Applied Physics (Japan); Kobayashi, T. [RIKEN Center for Advanced Photonics (Japan); Ueno, H. [RIKEN Nishina Center (Japan); Asahi, K. [Tokyo Institute of Technology, Department of Physics (Japan); Shimoda, T. [Osaka University, Department of Physics (Japan); Matsuo, Y. [Hosei University, Department of Advanced Sciences (Japan); Collaboration: OROCHI Collaboration
2015-11-15
A new laser spectroscopic method named “OROCHI (Optical RI-atom Observation in Condensed Helium as Ion catcher)” has been developed for deriving the nuclear spins and electromagnetic moments of low-yield exotic nuclei. In this method, we observe atomic Zeeman and hyperfine structures using laser-radio-frequency/microwave double-resonance spectroscopy. In our previous works, double-resonance spectroscopy was performed successfully with laser-sputtered stable atoms including non-alkali Au atoms as well as alkali Rb and Cs atoms. Following these works, measurements with {sup 84−87}Rb energetic ion beams were carried out in the RIKEN projectile fragment separator (RIPS). In this paper, we report the present status of OROCHI and discuss its feasibility, especially for low-yield nuclei such as unstable Au isotopes.
International Nuclear Information System (INIS)
A new laser spectroscopic method named “OROCHI (Optical RI-atom Observation in Condensed Helium as Ion catcher)” has been developed for deriving the nuclear spins and electromagnetic moments of low-yield exotic nuclei. In this method, we observe atomic Zeeman and hyperfine structures using laser-radio-frequency/microwave double-resonance spectroscopy. In our previous works, double-resonance spectroscopy was performed successfully with laser-sputtered stable atoms including non-alkali Au atoms as well as alkali Rb and Cs atoms. Following these works, measurements with 84−87Rb energetic ion beams were carried out in the RIKEN projectile fragment separator (RIPS). In this paper, we report the present status of OROCHI and discuss its feasibility, especially for low-yield nuclei such as unstable Au isotopes
Phase transitions and pairing signature in strongly attractive Fermi atomic gases
International Nuclear Information System (INIS)
We investigate pairing and quantum phase transitions in the one-dimensional two-component Fermi atomic gas in an external field. The phase diagram, critical fields, magnetization, and local pairing correlation are obtained analytically via the exact thermodynamic Bethe ansatz solution. At zero temperature, bound pairs of fermions with opposite spin states form a singlet ground state when the external field Hc1. A completely ferromagnetic phase without pairing occurs when the external field H>Hc2. In the region Hc1c2, we observe a mixed phase of matter in which paired and unpaired atoms coexist. The phase diagram is reminiscent of that of type II superconductors. For temperatures below the degenerate temperature and in the absence of an external field, the bound pairs of fermions form hard-core bosons obeying generalized exclusion statistics
Pederson, Mark R
2015-02-14
A recent modification of the Perdew-Zunger self-interaction-correction to the density-functional formalism has provided a framework for explicitly restoring unitary invariance to the expression for the total energy. The formalism depends upon construction of Löwdin orthonormalized Fermi-orbitals which parametrically depend on variational quasi-classical electronic positions. Derivatives of these quasi-classical electronic positions, required for efficient minimization of the self-interaction corrected energy, are derived and tested, here, on atoms. Total energies and ionization energies in closed-shell singlet atoms, where correlation is less important, using the Perdew-Wang 1992 Local Density Approximation (PW92) functional, are in good agreement with experiment and non-relativistic quantum-Monte-Carlo results albeit slightly too low. PMID:25681892
Pederson, Mark R
2014-01-01
A recent modification of the Perdew-Zunger self-interaction-correction (SIC) to the density-functional formalism (Pederson, Ruzsinszky, Perdew) has provided a framework for explicitly restoring unitary invariance to the expression for the total energy. The formalism depends upon construction of Lowdin orthonormalized Fermi-orbitals (Luken et al) which parametrically depend on variational quasi-classical electronic positions. Derivatives of these quasi-classical electronic positions, required for efficient minimization of the self-interaction corrected energy, are derived and tested here on atoms. Total energies and ionization energies in closed-shell atoms, where correlation is less important, using the PW92 LDA functional are in very good to excellent agreement with experiment and non-relativistic Quantum-Monte-Carlo (QMC) results.
Fermi-Bose mixtures of 40K and 87Rb atoms
International Nuclear Information System (INIS)
After the recent realization of the BCS-BEC crossover in dilute atomic Fermi gases, quantum degenerate mixtures of bosonic and fermionic atoms are expected to provide a complementary approach to fermionic super fluidity where the attractive interaction between Fermions is mediated by the inter species interaction, a situation which is in many ways analogous to phonon-mediated Cooper pairing in superconductors. Moreover, these mixtures are expected to show a rich phase diagram when loaded into an optical lattice, with various pairing phases involving one or several fermionic and bosonic atoms. Already in a harmonic trap, these mixtures show a rich class of phenomena. The behaviour of the mixture is influenced by a lot of properties: mean ld interaction both between Fermions and Bosons as well as the mean field interaction in the condensate. Depending on the sign of the Fermi-Bose interaction, phase separation or mean ld trapping and collapse of the mixture are expected. The mass ratio between Fermions and Bosons will also influence the ratio of trapping frequencies between the two species. Three-body loss processes can have a dramatic impact on lifetime and dynamical behaviour of the mixture. The condensate overlapping only with a small part of the Fermi sea will introduce localized trapping and loss processes. We report on the production of a quantum degenerate Fermi-Bose mixture of 40K and 87Rb in a regime of large particle numbers. In the experiment, we can span a wide range of phenomena starting at small particle numbers, where the expansion of the bosonic and the fermionic component are well described by the respective single-component Thomas-Fermi profiles. As particle numbers and densities in the mixture increase, the mean field attraction will create a strong localized mean field trapping potential in the centre of the trap where the BEC is localized. We observe this in-trap effect as a bimodal distribution of the fermionic component in the axial direction
Spin-orbit coupled two-electron Fermi gases of ytterbium atoms
Song, Bo; Zhang, Shanchao; Zou, Yueyang; Haciyev, Elnur; Huang, Wei; Liu, Xiong-Jun; Jo, Gyu-Boong
2016-01-01
We demonstrate the spin-orbit coupling (SOC) in a two-electron Fermi gas of $^{173}$Yb atoms by coupling two hyperfine ground states via the two-photon Raman transition. Due to the SU($N$) symmetry of the $^1$S$_0$ ground-state manifold which is insensitive to external magnetic field, an optical AC Stark effect is applied to split the ground spin states and separate an effective spin-1/2 subspace out from other hyperfine levels for the realization of SOC. With a momentum-dependent spin-orbit gap being suddenly opened by switching on the Raman transition, the dephasing of spin dynamics is observed, as a consequence of the momentum-dependent Rabi oscillations. Moreover, the momentum asymmetry of the spin-orbit coupled Fermi gas is also examined after projection onto the bare spin state and the corresponding momentum distribution is measured for different two-photon detuning. The realization of SOC for Yb fermions may open a new avenue to the study of novel spin-orbit physics with alkaline-earth-like atoms.
Evidence for ferromagnetic instability in a repulsive Fermi gas of ultracold atoms
Valtolina, G; Amico, A; Burchianti, A; Recati, A; Enss, T; Inguscio, M; Zaccanti, M; Roati, G
2016-01-01
Ferromagnetism is among the most spectacular manifestations of interactions within many-body fermion systems. In contrast to weak-coupling phenomena, it requires strong repulsion to develop, making a quantitative description of ferromagnetic materials notoriously difficult. This is especially true for itinerant ferromagnets, where magnetic moments are not localized into a crystal lattice. In particular, it is still debated whether the simplest case envisioned by Stoner of a homogeneous Fermi gas with short-range repulsive interactions can exhibit ferromagnetism at all. In this work, we positively answer this question by studying a clean model system consisting of a binary spin-mixture of ultracold 6Li atoms, whose repulsive interaction is tuned via a Feshbach resonance. We drastically limit detrimental pairing effects that affected previous studies by preparing the gas in a magnetic domain-wall configuration. We reveal the ferromagnetic instability by observing the softening of the spin-dipole collective mode...
Goodisman's correction of the Thomas-Fermi-von Weizsaecker theory of atoms
International Nuclear Information System (INIS)
Following a suggestion of J. Goodisman, we substitute the therm 3/5 γ0ρ5/3 by 3/5 γ0fzρ5/3 in the Thomas-Fermi-von Weizsaecker energy functional for atoms. fz: R3 → [0, 1] is a function depending on the nuclear charge z. We establish conditions for the functions fz such that the ratio of this modified TFW-energy EkzTFWG(z) (kz is the total number of electrons) and the exact quantum mechanical energy converges to 1 as z → ∞. Moreover, we prove that EkzTFWG(z) = EkzTFW(z) + Dz2 + o(z2) (z → ∞) and determine D. Here, EkzTFW(z) is the unmodified TFW energy. (orig.)
Page, Dany; Prakash, Madappa; Seiner, Andrew W
2013-01-01
Neutron stars provide a fertile environment for exploring superfluidity under extreme conditions. It is not surprising that Cooper pairing occurs in dense matter since nucleon pairing is observed in nuclei as energy differences between even-even and odd-even nuclei. Since superfluids and superconductors in neutron stars profoundly affect neutrino emissivities and specific heats, their presence can be observed in the thermal evolution of neutron stars. An ever-growing number of cooling neutron stars, now amounting to 13 thermal sources, and several additional objects from which upper limits to temperatures can be ascertained, can now be used to discriminate among theoretical scenarios and even to dramatically restrict properties of nucleon pairing at high densities. In addition, observations of pulsars, including their spin-downs and glitch histories, additionally support the conjecture that superfluidity and superconductivity are ubiquitous within, and important to our understanding of, neutron stars.
75 FR 20867 - DTE Energy; Enrico Fermi Atomic Power Plant, Unit 1
2010-04-21
..., Deputy Director, Decommissioning and Uranium Recovery Licensing Directorate, Division of Waste Management... Action DTE is in the process of decommissioning Fermi-1. During the decommissioning process,...
Fermi and Coulomb correlation effects upon the interacting quantum atoms energy partition
Ruiz, Isela; Holguín-Gallego, Fernando José; Francisco, Evelio; Pendás, Ángel Martín; Rocha-Rinza, Tomás
2016-01-01
The Interacting Quantum Atoms (IQA) electronic energy partition is an important method in the field of quantum chemical topology which has given important insights of different systems and processes in physical chemistry. There have been several attempts to include Electron Correlation (EC) in the IQA approach, for example, through DFT and Hartree-Fock/Coupled-Cluster (HF/CC) transition densities. This work addresses the separation of EC in Fermi and Coulomb correlation and its effect upon the IQA analysis by taking into account spin-dependent one- and two-electron matrices $D^{\\mathrm{HF/CC}}_{p\\sigma q \\sigma}$ and $d^{\\mathrm{HF/CC}}_{p\\sigma q\\sigma r\\tau s\\tau}$ wherein $\\sigma$ and $\\tau$ represent either of the $\\alpha$ and $\\beta$ spin projections. We illustrate this approach by considering BeH$_2$,BH, CN$^-$, HF, LiF, NO$^+$, LiH, H$_2$O$\\cdots$H$_2$O and C$_2$H$_2$, which comprise non-polar covalent, polar covalent, ionic and hydrogen bonded systems. The same and different spin contributions to ($i$...
Thermodynamics of interacting cold atomic Fermi gases with spin-orbit coupling
Jensen, Scott; Alhassid, Yoram; Gilbreth, Christopher
New physics is suggested with the prediction of novel phases in cold atom systems when a synthetic spin-orbit coupling is introduced. In particular, recent studies show that a new type of Bose-Einstein condensate, termed Rashbon-BEC, is formed when a generalized Rashba spin-orbit term is present. The Rashbon-BEC phase can be obtained by tuning the spin-orbit coupling strength even in the case of finite negative scattering length. This stands in contrast to the BCS-BEC crossover in the absence of spin-orbit coupling where a negative scattering length is associated with BCS physics, and its divergence signals the crossover. In our work we apply finite-temperature quantum Monte Carlo methods to a spherical Rashba spin-orbit coupled two-species Fermi gas with contact s-wave interaction in three dimensions. We will discuss the phase diagram for this system, and its crossover behavior from BCS to Rashbon-BEC. This work was supported in part by the Department of Energy Grant No. DE-FG-0291-ER-40608.
Structure of a quantized vortex near the BCS-BEC crossover in an atomic Fermi gas
International Nuclear Information System (INIS)
In order to clarify the structure of a singly quantized vortex in a superfluid fermion gas near the Feshbach resonance, we numerically solve the generalized Bogoliubov-de Gennes equation in the boson-fermion model. The superfluid gap, which contains contributions from both condensed fermion pairs and condensed bosons, is self-consistently determined, and the quasiparticle excitation levels bound in the vortex core are explicitly shown. We find that the boson condensate contributes to enhance the matter density depletion and the discreteness of localized quasiparticle spectrum inside the core. It is predicted that the matter density depletion and the discrete core levels are detectable in the vicinity of the BCS-Bose-Einstein condensation crossover point
Critical temperature of Bose-Einstein condensation in trapped atomic Bose-Fermi mixtures
International Nuclear Information System (INIS)
We calculate the shift in the critical temperature of Bose-Einstein condensation for a dilute Bose-Fermi mixture confined by a harmonic potential, to lowest order in both the Bose-Bose and Bose-Fermi coupling constants. The relative importance of the effect on the critical temperature of the boson-boson and boson-fermion interactions is investigated as a function of the parameters of the mixture. The possible relevance of the shift of the transition temperature in current experiments on trapped Bose-Fermi mixtures is discussed. (letter to the editor)
Critical temperature of Bose-Einstein condensation in trapped atomic Bose-Fermi mixtures
Energy Technology Data Exchange (ETDEWEB)
Albus, A P [Institut fuer Physik, Universitaet Potsdam, D-14469 Potsdam (Germany); Giorgini, S [Dipartimento di Fisica, Universita di Trento, and Istituto Nazionale per la Fisica della Materia, I-38050 Povo (Italy); Illuminati, F [Dipartimento di Fisica, Universita di Salerno, and Istituto Nazionale per la Fisica della Materia, I-84081 Baronissi (Italy); Viverit, L [Dipartimento di Fisica, Universita di Trento, and Istituto Nazionale per la Fisica della Materia, I-38050 Povo (Italy)
2002-12-14
We calculate the shift in the critical temperature of Bose-Einstein condensation for a dilute Bose-Fermi mixture confined by a harmonic potential, to lowest order in both the Bose-Bose and Bose-Fermi coupling constants. The relative importance of the effect on the critical temperature of the boson-boson and boson-fermion interactions is investigated as a function of the parameters of the mixture. The possible relevance of the shift of the transition temperature in current experiments on trapped Bose-Fermi mixtures is discussed. (letter to the editor)
Ultracold Fermi-Fermi Mixtures of Lithium and Potassium
International Nuclear Information System (INIS)
Ultracold atomic Fermi gases are a unique experimental tool for simulating and studying many-body systems. Since they are very well controllable and clean systems with tunable interactions, they can serve as quantum simulators for effects that occur in solid states and usually arise from the quantum nature of the Fermi gas of electrons. Different phenomena such as high-temperature superconductivity, Josephson junctions and ferromagnetism can be explored using degenerate Fermi gases. Even in the context of particle physics, Fermi gases can be used to simulate the behavior of quarks inside a nucleus. In the past decade, experiments with a single fermionic (either 6Li or 40K) species have led to ground breaking results. In the past five years, several experiments have been set up that combine the two fermionic alkali species. Additionally to the capabilities offered by a single-species experiment (such as tuning of interaction strength, spin polarization, trap parameters), the two-species mixtures open up control of new parameters - the most obvious being the mass ratio. Due to the mass-imbalance, the Fermi-spheres would no longer overlap, and thus exotic quantum phases emerge. So far experimentally unobserved effects include superfluidity, phase separation, crystalline phases, exotic pairing mechanisms and long-lived trimers. More practically, a mixture would allow to species-selectively apply optical trapping potentials. This thesis presents the experimental efforts from creating an ultracold Fermi- Fermi mixture of 6Li and 40K to the creation of heteronuclear molecules. Three published articles are contained in this thesis. In the first article we report on the observation of Feshbach resonances in an ultracold mixture of two fermionic species, 6Li and 40K. The experimental data are interpreted using a simple asymptotic bound state model and full coupled channels calculations. This unambiguously assigns the observed resonances in terms of various s- and p
Low temperatures shear viscosity of a two-component dipolar Fermi gas with unequal population
Darsheshdar, E.; Yavari, H.; Zangeneh, Z.
2016-07-01
By using the Green's functions method and linear response theory we calculate the shear viscosity of a two-component dipolar Fermi gas with population imbalance (spin polarized) in the low temperatures limit. In the strong-coupling Bose-Einstein condensation (BEC) region where a Feshbach resonance gives rise to tightly bound dimer molecules, a spin-polarized Fermi superfluid reduces to a simple Bose-Fermi mixture of Bose-condensed dimers and the leftover unpaired fermions (atoms). The interactions between dimer-atom, dimer-dimer, and atom-atom take into account to the viscous relaxation time (τη) . By evaluating the self-energies in the ladder approximation we determine the relaxation times due to dimer-atom (τDA) , dimer-dimer (τcDD ,τdDD) , and atom-atom (τAA) interactions. We will show that relaxation rates due to these interactions τDA-1 ,τcDD-1, τdDD-1, and τAA-1 have T2, T4, e - E /kB T (E is the spectrum of the dimer atoms), and T 3 / 2 behavior respectively in the low temperature limit (T → 0) and consequently, the atom-atom interaction plays the dominant role in the shear viscosity in this rang of temperatures. For small polarization (τDA ,τAA ≫τcDD ,τdDD), the low temperatures shear viscosity is determined by contact interaction between dimers and the shear viscosity varies as T-5 which has the same behavior as the viscosity of other superfluid systems such as superfluid neutron stars, and liquid helium.
International Nuclear Information System (INIS)
This report describes simulation study results on the research for superconducting (superfluid) neutron detector device and related fundamental issues on nano-structured superconductors in the fiscal year 2008. At first, in order to examine a performance of a neutron detector using superfluid He3, we make large-scale numerical simulations on non-equilibrium superfluid dynamics after a neutron capture below the superfluid transition temperature by solving the Gross-Pitaevskii equation. The simulations whose largest grid size is 2O483 on the Earth Simulator successfully reproduce the vortex nucleation and reveal the non-equilibrium dynamics of decay superfluid turbulence. On the other hand, as a fundamental research issue of this project, we numerically investigate the ground state of a two-band Hubbard model by using the exact-diagonalization method developed with this project to examine a superconducting mechanism for iron-based high-Tc superconductors discovered by Hosono's group in February 2008. By employing the exact-diagonalization as a large-scale numerical tool, we reveal that a robust and novel type of superconductivity widely emerges when the inter-band repulsion becomes stronger than the intra-band one. Although such a situation is un-usual in solid state matters, the atomic Fermi gases may easily create the situation. (author)
Dynamics of quantised vortices in superfluids
Sonin, Edouard B
2016-01-01
A comprehensive overview of the basic principles of vortex dynamics in superfluids, this book addresses the problems of vortex dynamics in all three superfluids available in laboratories (4He, 3He, and BEC of cold atoms) alongside discussions of the elasticity of vortices, forces on vortices, and vortex mass. Beginning with a summary of classical hydrodynamics, the book guides the reader through examinations of vortex dynamics from large scales to the microscopic scale. Topics such as vortex arrays in rotating superfluids, bound states in vortex cores and interaction of vortices with quasiparticles are discussed. The final chapter of the book considers implications of vortex dynamics to superfluid turbulence using simple scaling and symmetry arguments. Written from a unified point of view that avoids complicated mathematical approaches, this text is ideal for students and researchers working with vortex dynamics in superfluids, superconductors, magnetically ordered materials, neutron stars and cosmological mo...
Critical temperature of Bose-Einstein condensation in trapped atomic Bose-Fermi mixtures
Albus, Alexander P.; Giorgini, Stefano; Illuminati, Fabrizio; Viverit, Luciano
2002-01-01
We calculate the shift in the critical temperature of Bose-Einstein condensation for a dilute Bose-Fermi mixture confined by a harmonic potential to lowest order in both the Bose-Bose and Bose-Fermi coupling constants. The relative importance of the effect on the critical temperature of the boson-boson and boson-fermion interactions is investigated as a function of the parameters of the mixture. The possible relevance of the shift of the transition temperature in current experiments on trappe...
Quantum-Shell Corrections to the Finite-Temperature Thomas-Fermi-Dirac Statistical Model of the Atom
Energy Technology Data Exchange (ETDEWEB)
Ritchie, A B
2003-07-22
Quantum-shell corrections are made directly to the finite-temperature Thomas-Fermi-Dirac statistical model of the atom by a partition of the electronic density into bound and free components. The bound component is calculated using analytic basis functions whose parameters are chosen to minimize the energy. Poisson's equation is solved for the modified density, thereby avoiding the need to solve Schroedinger's equation for a self-consistent field. The shock Hugoniot is calculated for aluminum: shell effects characteristic of quantum self-consistent field models are fully captures by the present model.
On the role of the uncertainty principle in superconductivity and superfluidity
Institute of Scientific and Technical Information of China (English)
Roberto Onofrio
2012-01-01
We discuss the general interplay between the uncertainty principle and the onset of dissipationless transport phenomena such as superconductivity and superfluidity.We argue that these phenomena are possible because of the robustness of many-body quantum states with respect to the external environment,which is directly related to the uncertainty principle as applied to coordinates and momenta of the carriers.In the case of superconductors,this implies relationships between macroscopic quantities such as critical temperature and critical magnetic field,and microscopic quantities such as the amount of spatial squeezing of a Cooper pair and its correlation time.In the case of ultracold atomic Fermi gases,this should be paralleled by a connection between the critical temperature for the onset of superfluidity and the corresponding critical velocity.Tests of this conjecture are finally sketched with particular regard to the understanding of the behaviour of superconductors under external pressures or mesoscopic superconductors,and the possibility to mimic these effects in ultracold atomic Fermi gases using Feshbach resonances and atomic squeezed states.
Strongly interacting Fermi gases
Directory of Open Access Journals (Sweden)
Bakr W.
2013-08-01
Full Text Available Strongly interacting gases of ultracold fermions have become an amazingly rich test-bed for many-body theories of fermionic matter. Here we present our recent experiments on these systems. Firstly, we discuss high-precision measurements on the thermodynamics of a strongly interacting Fermi gas across the superfluid transition. The onset of superfluidity is directly observed in the compressibility, the chemical potential, the entropy, and the heat capacity. Our measurements provide benchmarks for current many-body theories on strongly interacting fermions. Secondly, we have studied the evolution of fermion pairing from three to two dimensions in these gases, relating to the physics of layered superconductors. In the presence of p-wave interactions, Fermi gases are predicted to display toplogical superfluidity carrying Majorana edge states. Two possible avenues in this direction are discussed, our creation and direct observation of spin-orbit coupling in Fermi gases and the creation of fermionic molecules of 23Na 40K that will feature strong dipolar interactions in their absolute ground state.
International Nuclear Information System (INIS)
The Thomas-Fermi (TF) and Thomas-Fermi-von Weizsacker (TFW) theories of atoms and molecules with electron-electron repulsion are reviewed briefly. The main difference between the energies, E/sup TFW/ - E/sup TF/ (for large z), is a term D/sup TFW/z2. (It is also believed that E/sup Q/ - E/sup TF/ approx. D/sup Q/z2, where E/sup Q/ is the true quantum ground state energy). To calculate D/sup TFW/, it is necessary to find the positive solution to the differential equation: ]- Δ + vertical bar psi(x) vertical bar/sup 4/3/ - vertical bar x vertical bar-1] psi(x) = 0 in three dimensions. While this equation arises from TFW theory with electron-electron repulsion, it also has a second interpretation - namely as the TFW equation for an atom without electron-electron repulsion. The main content of this report is the numerical solution of this equation and the evaluation of D/sup TFW/
Pair Correlations in Superfluid Helium 3
Vollhardt, D.
1997-01-01
In 1996 Lee, Osheroff and Richardson received the Nobel Prize for their 1971 discovery of superfluid helium 3 -- a discovery which opened the door to the most fascinating system known in condensed matter physics. The superfluid phases of helium 3, originating from pair condensation of helium 3 atoms, turned out to be the ideal test-system for many fundamental concepts of modern physics, such as macroscopic quantum phenomena, (gauge-)symmetries and their spontaneous breakdown, topological defe...
Faraday waves in elongated superfluid fermionic clouds
Capuzzi, P.; Vignolo, P.
2008-01-01
We use hydrodynamic equations to study the formation of Faraday waves in a superfluid Fermi gas at zero temperature confined in a strongly elongated cigar-shaped trap. First, we treat the role of the radial density profile in the limit of an infinite cylindrical geometry and analytically evaluate the wavelength of the Faraday pattern. The effect of the axial confinement is fully taken into account in the numerical solution of hydrodynamic equations and shows that the infinite cylinder geometr...
Theory of open Fermi systems for description of atomic nuclei and nuclear reactions
International Nuclear Information System (INIS)
The Leman expansion for exact single-particle Green function, taking into account the continuous spectrum states of an open Fermi system, is built. The analytical properties of the elastic scattering S-matrix and Green function are investigated, taking into account ground state correlations. On the base of the projection operator method the Leman expansion of mass operators and equations of the unified theory of nuclear reactions are found. The conclusion is drawn on the coincidence of the mean field, real part of optical potential for global average scheme and generalized Hartree-Fock potential is done. The character of fluctuations of the optical potential parameters for the transition from the global set to individual sets and their connection with the dispersion relation are described
Mixtures of Bosonic and Fermionic Atoms in Optical Lattices
Albus, Alexander; Illuminati, Fabrizio; Eisert, Jens
2003-01-01
We discuss the theory of mixtures of Bosonic and Fermionic atoms in periodic potentials at zero temperature. We derive a general Bose--Fermi Hubbard Hamiltonian in a one--dimensional optical lattice with a superimposed harmonic trapping potential. We study the conditions for linear stability of the mixture and derive a mean field criterion for the onset of a Bosonic superfluid transition. We investigate the ground state properties of the mixture in the Gutzwiller formulation of mean field the...
International Nuclear Information System (INIS)
Supplement No. 4 to the Safety Evaluation Report related to the operation of the Enrico Fermi Atomic Power Plant, Unit 2, provides the staff's evaluation of additional information submitted by the applicant regarding outstanding review issues identified in Supplement No. 3 to the Safety Evaluation Report, dated January 1983
International Nuclear Information System (INIS)
Supplement No. 3 to the Safety Evaluation Report related to the operation of the Enrico Fermi Atomic Power Plant, Unit 2, provides the staff's evaluation of additional information submitted by the applicant regarding outstanding review issues identified in Supplement No. 2 to the Safety Evaluation Report, dated January 1982
Strong Coupling Effects on the Specific Heat of an Ultracold Fermi Gas in the Unitarity Limit
van Wyk, P.; Tajima, H.; Hanai, R.; Ohashi, Y.
2016-05-01
We investigate strong-coupling corrections to the specific heat C_V in the normal state of an ultracold Fermi gas in the BCS-BEC crossover region. A recent experiment on a ^6Li unitary Fermi gas (Ku et. al. in Science 335:563 2012) shows that C_V is remarkably amplified near the superfluid phase transition temperature T_c, being similar to the well-known λ -structure observed in liquid ^4He. Including pairing fluctuations within the framework of the strong-coupling theory developed by Nozières and Schmitt-Rink, we show that strong pairing fluctuations are sufficient to explain the anomalous behavior of C_V observed in a ^6Li unitary Fermi gas near T_c. We also show that there is no contribution from stable preformed Cooper pairs to C_V at the unitarity. This indicates that the origin of the observed anomaly is fundamentally different from the case of liquid 4He, where stable ^4He Bose atoms induce the λ -structure in C_V near the superfluid instability. Instead, the origin is the suppression of the entropy S, near T_c, due to the increase of metastable preformed Cooper pairs. Our results indicate that the specific heat is a useful quantity to study the effects of pairing fluctuations on the thermodynamic properties of an ultracold Fermi gas in the BCS-BEC crossover region.
Chiral Magnetic "Superfluidity"
Sadofyev, Andrey V
2015-01-01
We study a heavy impurity moving longitudinal with the direction of an external magnetic field in an anomalous chiral medium. Such system would carry a non-dissipative current of chiral magnetic effect associated with the anomaly. We show, by generalizing Landau's criterion for superfluidity, that the "anomalous component" which gives rise to the anomalous transport will {\\it not} contribute to the drag experienced by an impurity. We argue on very general basis that those systems with a strong magnetic field would exhibit the behavior of 'superfluidity" -- the motion of the heavy impurity is frictionless, in analog to the case of a superfluid. However, this "superfluidity" exists even for chiral media at finite temperature and only in the directional longitudinal with the magnetic field, in contrast to the ordinary superfluid. We will call this novel phenomenon as the Chiral Magnetic "Superfluidity". We demonstrate and confirm our general results with two complementary examples: weakly coupled chiral fermion ...
Khoury, Justin
2016-01-01
In this talk I summarize a novel framework that unifies the stunning success of MOND on galactic scales with the triumph of the $\\Lambda$CDM model on cosmological scales. This is achieved through the rich and well-studied physics of superfluidity. The dark matter and MOND components have a common origin, representing different phases of a single underlying substance. In galaxies, dark matter thermalizes and condenses to form a superfluid phase. The superfluid phonons couple to baryonic matter...
A molecular Bose-Einstein condensate emerges from a Fermi sea
Greiner, Markus; Regal, Cindy A.; Jin, Deborah S.
2003-01-01
The realization of fermionic superfluidity in a dilute gas of atoms, analogous to superconductivity in metals, is a long-standing goal of ultracold gas research. Beyond being a new example of this fascinating quantum phenomenon, fermionic superfluidity in an atomic gas holds the promise of adjustable interactions and the ability to tune continuously from BCS-type superfluidity to Bose-Einstein condensation (BEC). This crossover between BCS superfluidity of correlated atom pairs in momentum sp...
Josephson gyroscope using superfluids
International Nuclear Information System (INIS)
The Sagnac effect using matter (de Broglie) waves is considered for gyroscopic applications. Superfluid helium in a torus with a Josephson junction interrupting it would be an embodiment of this idea. An optical analog of the Josephson junction is discussed. An experimental search for the Sagnac effect in superfluid helium (isotope 4) is presented. 5 references
Langlois, David
2001-01-01
Neutron stars are believed to contain (neutron and proton) superfluids. I will give a summary of a macroscopic description of the interior of neutron stars, in a formulation which is general relativistic. I will also present recent results on the oscillations of neutron stars, with superfluidity explicitly taken into account, which leads in particular to the existence of a new class of modes.
2010-10-18
.... Nuclear Regulatory Commission (NRC or the Commission) now or hereafter in effect. Fermi 1 was a fast breeder reactor power plant cooled by sodium and operated at essentially atmospheric pressure. In November... in Monroe County, Michigan. Fermi 1 is a permanently shutdown nuclear reactor facility. The...
International Nuclear Information System (INIS)
The Moliere approximation to the Thomas-Fermi screening function was used in a screened Coulomb potential to calculate tables of differential scattering cross sections for laboratory scattering angles of 90 and 1380. Data are provided for incident ions of 3He+ and 20Ne+ as a function of energy (0.05 to 5.0 keV) and target atom. 3 references
International Nuclear Information System (INIS)
The Fermi-Segre normalization expression is rederived for arbitrary orbital angular momentum l within the context of a generalized WKB method. Results from the approximation are compared with calculations employing Hartree-Slater atomic potentials
Strong Correlations in Ultracold Fermi Gases
Schneider, William
Ultracold atomic gases provide an ideal system with which to study fundamental manybody physics. Exhibiting universal interactions in clean and controllable environments, long-used simple models as well as more exotic models can now be realized. The interplay between theory and experiment is therefore very active, and, in this thesis, I will detail several works, both exact analytic results and numerical calculations, which have impacts on current experiments. I begin with an introduction to the field including a brief discussion of experiments, the microscopic model of two species of interacting fermions, the BCS-BEC crossover and an overview of the various phases of atomic Fermi gases. I then describe the various results of my theoretical investigations, which are divided into five chapters. First, I describe radio frequency (RF) spectroscopy experiments and how they probe the single-particle spectral function. This leads to my results on an exact feature of the spectral lineshape, a universal large-momentum structure which exists for all states of interacting Fermi systems and has been verified in recent angle-resolved RF experiments. Second, I focus on gases which have a normal Fermi liquid ground state and show that their lineshape exhibits a characteristic jump discontinuity. I illustrate this Fermi surface singularity and the previously mentioned universal large momentum tail with explicit calculations. Third, I turn to the low energy structure of the single-particle spectral function in the superfluid state. I argue that sharp low energy quasiparticle excitations exist across the BCS-BEC crossover using a general argument that includes the interaction of fermions with the low-energy collective mode. This is illustrated with an explicit calculation within an approximation scheme. Fourth, I address the trap-induced inhomogeneity and use a Bogoliubov-deGennes analysis to test if a simple local density approximation (LDA) can provide an adequate description of
$^3P_2$ Superfluids Are Topological
Mizushima, Takeshi
2016-01-01
We clarify the topology of the $^3P_2$ superfluidity which is expected to be realized in the cores of neutron stars and cubic odd-parity superconductors. The phase diagram includes the unitary uniaxial/biaxial nematic phases and nonunitary ferromagnetic and cyclic phases. We here show that the low-energy structures of all the phases are governed by different types of topologically protected gapless fermionic excitations: Surface Majorana fermions in nematic phases, single itinerant Majorana fermion in the ferromagnetic phase, and a quartet of itinerant Majorana fermions in the cyclic phase. Using the superfluid Fermi liquid theory, we also demonstrate that dihedral-two and -four biaxial nematic phases are thermodynamically favored in the weak coupling limit under a magnetic field. The mass acquisition of surface Majorana fermions in nematic phases is subject to symmetry.
Energy Technology Data Exchange (ETDEWEB)
Erika Bailey
2011-07-07
The Enrico Fermi Atomic Power Plant, Unit 1 (Fermi 1) was a fast breeder reactor design that was cooled by sodium and operated at essentially atmospheric pressure. On May 10, 1963, the Atomic Energy Commission (AEC) granted an operating license, DPR-9, to the Power Reactor Development Company (PRDC), a consortium specifically formed to own and operate a nuclear reactor at the Fermi 1 site. The reactor was designed for a maximum capability of 430 megawatts (MW); however, the maximum reactor power with the first core loading (Core A) was 200 MW. The primary system was filled with sodium in December 1960 and criticality was achieved in August 1963.
Superfluid Brillouin Optomechanics
Kashkanova, A D; Brown, C D; Flowers-Jacobs, N E; Childress, L; Hoch, S W; Hohmann, L; Ott, K; Reichel, J; Harris, J G E
2016-01-01
Optomechanical systems couple an electromagnetic cavity to a mechanical resonator which is typically formed from a solid object. The range of phenomena accessible to these systems depends on the properties of the mechanical resonator and on the manner in which it couples to the cavity fields. In both respects, a mechanical resonator formed from superfluid liquid helium offers several appealing features: low electromagnetic absorption, high thermal conductivity, vanishing viscosity, well-understood mechanical loss, and in situ alignment with cryogenic cavities. In addition, it offers degrees of freedom that differ qualitatively from those of a solid. Here, we describe an optomechanical system consisting of a miniature optical cavity filled with superfluid helium. The cavity mirrors define optical and mechanical modes with near-perfect overlap, resulting in an optomechanical coupling rate ~3 kHz. This coupling is used to drive the superfluid; it is also used to observe the superfluid's thermal motion, resolving...
Faraday waves in elongated superfluid fermionic clouds
Capuzzi, P.; Vignolo, P.
2008-10-01
We use hydrodynamic equations to study the formation of Faraday waves in a superfluid Fermi gas at zero temperature confined in a strongly elongated cigar-shaped trap. First, we treat the role of the radial density profile in the limit of an infinite cylindrical geometry and analytically evaluate the wavelength of the Faraday pattern. The effect of the axial confinement is fully taken into account in the numerical solution of hydrodynamic equations, and shows that the infinite cylinder geometry provides a very good description of the phenomena.
Neutrino emissivity of anisotropic neutron superfluids
Leinson, L. B.
2013-01-01
We examine the influence of the anisotropy of the superfluid energy gap and residual Fermi-liquid interactions in the triplet-correlated neutron liquid onto neutrino energy losses through neutral weak currents. The neutrino-pair emission caused by the pair breaking and formation processes and by the spin-wave decays is considered for the case of the $^{3}P_{2}$ pairing in the state with $m_{j}=0$. The simple analytical formulae are obtained. A comparison with the previous results of the avera...
Flowing holographic anyonic superfluid
Jokela, Niko; Lifschytz, Gilad; Lippert, Matthew
2014-01-01
We investigate the flow of a strongly coupled anyonic superfluid based on the holographic D3-D7' probe brane model. By analyzing the spectrum of fluctuations, we find the critical superfluid velocity, as a function of the temperature, at which the flow stops being dissipationless when flowing past a barrier. We find that at a larger velocity the flow becomes unstable even in the absence of a barrier.
Anomalous Chiral Superfluidity
Lublinsky, Michael(Physics Department, Ben-Gurion University of the Negev, Beer Sheva 84105, Israel); Zahed, Ismail
2009-01-01
We discuss both the anomalous Cartan currents and the energy-momentum tensor in a left chiral theory with flavour anomalies as an effective theory for flavored chiral phonons in a chiral superfluid with the gauged Wess-Zumino-Witten term. In the mean-field (leading tadpole) approximation the anomalous Cartan currents and the energy momentum tensor take the form of constitutive currents in the chiral superfluid state. The pertinence of higher order corrections and the Adler-Bardeen theorem is ...
Khoury, Justin
2016-01-01
In this talk I summarize a novel framework that unifies the stunning success of MOND on galactic scales with the triumph of the $\\Lambda$CDM model on cosmological scales. This is achieved through the rich and well-studied physics of superfluidity. The dark matter and MOND components have a common origin, representing different phases of a single underlying substance. In galaxies, dark matter thermalizes and condenses to form a superfluid phase. The superfluid phonons couple to baryonic matter particles and mediate a MOND-like force. This framework naturally distinguishes between galaxies (where MOND is successful) and galaxy clusters (where MOND is not): dark matter has a higher temperature in clusters, and hence is in a mixture of superfluid and normal phase. The rich and well-studied physics of superfluidity leads to a number of striking observational signatures, which we briefly discuss. Remarkably the critical temperature and equation of state of the dark matter superfluid are similar to those of known co...
Khoury, Justin
2015-01-01
In this talk we present a novel framework that unifies the stunning success of MOND on galactic scales with the triumph of the LambdaCDM model on cosmological scales. This is achieved through the rich and well-studied physics of superfluidity. The dark matter and MOND components have a common origin, representing different phases of a single underlying substance. In galaxies, dark matter thermalizes and condenses to form a superfluid phase. The superfluid phonons couple to baryonic matter particles and mediate a MOND-like force. Our framework naturally distinguishes between galaxies (where MOND is successful) and galaxy clusters (where MOND is not): dark matter has a higher temperature in clusters, and hence is in a mixture of superfluid and normal phase. The rich and well-studied physics of superfluidity leads to a number of striking observational signatures, which we briefly discuss. Remarkably the critical temperature and equation of state of the dark matter superfluid are similar to those of known cold at...
Spontaneous quantum Hall effect in an atomic spinor Bose-Fer mi mixture
Xu, Zhi-Fang; Li, Xiaopeng; Zoller, Peter; Liu, W. Vincent
2015-03-01
We study a mixture of spin-1 bosonic and spin-1/2 fermionic cold atoms, e.g., Rb-87 and Li-6,confined in a triangular optical lattice. With fermions at 3/4 filling, Fermi surface nesting leads to spontaneous formation of various spin textures of bosons in the ground state, such as collinear, coplanar and even non-coplanar spin orders. The phase diagram is mapped out with varying boson tunneling and Bose-Fermi interactions. Most significantly, in one non-coplanar state the mixture is found to exhibit spontaneous quantum Hall effect in fermions and crystalline superfluidity in bosons, both driven by interaction.
Okazaki, K; Ito, Y.; Ota, Y; Kotani, Y.; Shimojima, T.; Kiss, T.; Watanabe, S; C.-T. Chen; S. Niitaka; Hanaguri, T; Takagi, H.; Chainani, A.; Shin, S.
2014-01-01
Conventional superconductivity follows Bardeen-Cooper-Schrieffer(BCS) theory of electrons-pairing in momentum-space, while superfluidity is the Bose-Einstein condensation(BEC) of atoms paired in real-space. These properties of solid metals and ultra-cold gases, respectively, are connected by the BCS-BEC crossover. Here we investigate the band dispersions in FeTe$_{0.6}$Se$_{0.4}$($T_c$ = 14.5 K $\\sim$ 1.2 meV) in an accessible range below and above the Fermi level($E_F$) using ultra-high reso...
Mott states under the influence of fermion-boson conversion: invasion of superfluidity
Zhou, Fei
2005-01-01
I study the influence of fermion-boson conversion near Feshbach resonances on Mott states of Cooper pairs and demonstrate possible invasion of superfluidity. The quantum dynamics of Fermi-Bose gases is studied using both an effective coupled $U(1)\\otimes U(1)$ quantum rotor Hamiltonian and a coupled XXZ $\\otimes$ XXZ spin Hamiltonian. I also point out two distinct branches of collective modes in superfluid states, one of which involves anti-symmetric phase oscillations in fermionic and bosoni...
Byers, N
2002-01-01
This talk is about Enrico Fermi and Leo Szilard, their collaboration and involvement in nuclear energy development and decisions to construct and use the atomic bomb in World War II. Fermi and Szilard worked closely together at Columbia in 1939-40 to explore feasibility of a nuclear chain reaction, and then on the physics for construction of the first pile (nuclear reactor). "On matters scientific or technical there was rarely any disagreement between Fermi and myself" Szilard said. But there were sharp differences on other matters.
Cruz, Salvador A.
An assessment of the use of statistical atomic models for the study of many-electron atom confinement is presented. The Thomas-Fermi-Dirac-[lambda]-Weizsäcker TFD[lambda]W functional formalism based on known properties of the orbital electron density is shown to be an appropriate tool for the description of the ground-state energy evolution of many-electron atoms spatially limited by closed and open boundaries. A brief review of the strategy followed in the TFD[lambda]W method for the study of atoms enclosed in hard and soft spherical cavities is presented along with more refined quantitative calculations as compared with previous results. Also, detailed quantitative results are shown-for the first time-in the case of confinement by a hard prolate spheroidal box for nuclear positions located at one of the foci and for an atom located at a distance D from a hard plane. A discussion is presented on the physical consequences of different confinement geometries and the adequacy of the TFD[lambda]W formalism to explore many-electron atom confinement by open and closed boundaries.
Exploring the thermodynamics of a universal Fermi gas
Nascimbène, S.; Navon, N.; Jiang, K. J.; Chevy, F.; Salomon, C.
2010-02-01
One of the greatest challenges in modern physics is to understand the behaviour of an ensemble of strongly interacting particles. A class of quantum many-body systems (such as neutron star matter and cold Fermi gases) share the same universal thermodynamic properties when interactions reach the maximum effective value allowed by quantum mechanics, the so-called unitary limit. This makes it possible in principle to simulate some astrophysical phenomena inside the highly controlled environment of an atomic physics laboratory. Previous work on the thermodynamics of a two-component Fermi gas led to thermodynamic quantities averaged over the trap, making comparisons with many-body theories developed for uniform gases difficult. Here we develop a general experimental method that yields the equation of state of a uniform gas, as well as enabling a detailed comparison with existing theories. The precision of our equation of state leads to new physical insights into the unitary gas. For the unpolarized gas, we show that the low-temperature thermodynamics of the strongly interacting normal phase is well described by Fermi liquid theory, and we localize the superfluid transition. For a spin-polarized system, our equation of state at zero temperature has a 2 per cent accuracy and extends work on the phase diagram to a new regime of precision. We show in particular that, despite strong interactions, the normal phase behaves as a mixture of two ideal gases: a Fermi gas of bare majority atoms and a non-interacting gas of dressed quasi-particles, the fermionic polarons.
Superfluid Helium 3: Link between Condensed Matter Physics and Particle Physics
Vollhardt, D.; Woelfle, P.
2000-01-01
The discovery of the superfluid phases of Helium 3 in 1971 opened the door to one of the most fascinating systems known in condensed matter physics. Superfluidity of Helium 3, originating from pair condensation of Helium 3 atoms, turned out to be the ideal testground for many fundamental concepts of modern physics, such as macroscopic quantum phenomena, (gauge-)symmetries and their spontaneous breakdown, topological defects, etc. Thereby the superfluid phases of Helium 3 enriched condensed ma...
Kalaydzhyan, Tigran
2014-01-01
We argue that the strongly coupled quark-gluon plasma formed at LHC and RHIC can be considered as a chiral superfluid. The "normal" component of the fluid is the thermalized matter in common sense, while the "superfluid" part consists of long wavelength (chiral) fermionic states moving independently. We use the bosonization procedure with a finite cut-off and obtain a dynamical axion-like field out of the chiral fermionic modes. Then we use relativistic hydrodynamics for macroscopic description of the effective theory obtained after the bosonization. Finally, solving the hydrodynamic equations in gradient expansion, we find that in the presence of external electromagnetic fields or rotation the motion of the "superfluid" component gives rise to the chiral magnetic, chiral vortical, chiral electric and dipole wave effects. Latter two effects are specific for a two-component fluid, which provides us with crucial experimental tests of the model.
Directory of Open Access Journals (Sweden)
Tőkési K.
2014-01-01
Full Text Available The ionization of Ar by 15 keV N+ ion is studied theoretically. The energy distributions of the ejected electrons as a function of the scattering angle were calculated using the classical trajectory Monte Carlo method. We identify the signature of the Fermi-shuttle type ionization in the double differential cross sections which should be a possible source of the high energy electrons in the plasma. Our classical calculation also describes the previously measured data with high accuracy.
Frustration and time-reversal symmetry breaking for Fermi and Bose-Fermi systems
Sacha, Krzysztof; Targońska, Katarzyna; Zakrzewski, Jakub
2012-05-01
The modulation of an optical lattice potential that breaks time-reversal symmetry enables the realization of complex tunneling amplitudes in the corresponding tight-binding model. For a superfluid Fermi gas in a triangular lattice potential with complex tunnelings, the pairing function acquires a complex phase, so the frustrated magnetism of fermions can be realized. Bose-Fermi mixtures of bosonic molecules and unbound fermions in the lattice also show interesting behavior. Due to boson-fermion coupling, the fermions become enslaved by the bosons and the corresponding pairing function takes the complex phase determined by the bosons. In the presence of bosons the Fermi system can reveal both gapped and gapless superfluidity.
Chang, Soon Yong
2008-04-01
In the recent years, dilute Fermi gases have played the center stage role in the many-body physics. The gas of neutral alkali atoms such as Lithium-6 and Potassium-40 can be trapped at temperatures below the Fermi degeneracy. The most relevant feature of these gases is that the interaction is tunable and strongly interacting superfluid can be artificially created. I will discuss the recent progress in understanding the ground state properties of the dilute Fermi gases at different interaction regimes. First, I will present the case of the spin symmetric systems where the Fermi gas can smoothly crossover from the BCS regime to the BEC regime. Then, I will discuss the case of the spin polarized systems, where different quantum phases can occur as a function of the polarization. In the laboratory, the trapped Fermi gas shows spatial dependence of the different quantum phases. This can be understood in the context of the local variation of the chemical potential. I will present the most accurate quantum ab initio results and the relevant experiments.
Sound modes in holographic superfluids
Herzog, Christopher P.; Yarom, Amos
2009-01-01
Superfluids support many different types of sound waves. We investigate the relation between the sound waves in a relativistic and a non-relativistic superfluid by using hydrodynamics to calculate the various sound speeds. Then, using a particular holographic scalar gravity realization of a strongly interacting superfluid, we compute first, second and fourth sound speeds as a function of the temperature. The relativistic low temperature results for second sound differ from Landau's well known...
Superfluid thermodynamic cycle refrigerator
Swift, Gregory W.; Kotsubo, Vincent Y.
1992-01-01
A cryogenic refrigerator cools a heat source by cyclically concentrating and diluting the amount of .sup.3 He in a single phase .sup.3 He-.sup.4 He solution. The .sup.3 He in superfluid .sup.4 He acts in a manner of an ideal gas in a vacuum. Thus, refrigeration is obtained using any conventional thermal cycle, but preferably a Stirling or Carnot cycle. A single phase solution of liquid .sup.3 He at an initial concentration in superfluid .sup.4 He is contained in a first variable volume connected to a second variable volume through a superleak device that enables free passage of .sup.4 He while restricting passage of .sup.3 He. The .sup.3 He is compressed (concentrated) and expanded (diluted) in a phased manner to carry out the selected thermal cycle to remove heat from the heat load for cooling below 1 K.
Superfluid thermodynamic cycle refrigerator
International Nuclear Information System (INIS)
A cryogenic refrigerator cools a heat source by cyclically concentrating and diluting the amount of 3He in a single phase 3He-4He solution. The 3He in superfluid 4He acts in a manner of an ideal gas in a vacuum. Thus, refrigeration is obtained using any conventional thermal cycle, but preferably a Stirling or Carnot cycle. A single phase solution of liquid 3He at an initial concentration in superfluid 4He is contained in a first variable volume connected to a second variable volume through a superleak device that enables free passage of 4He while restricting passage of 3He. The 3He is compressed (concentrated) and expanded (diluted) in a phased manner to carry out the selected thermal cycle to remove heat from the heat load for cooling below 1 K. 12 figs
Topological Superconductivity and Superfluidity
Qi, Xiao-Liang; Hughes, Taylor L.; Raghu, Srinivas; Zhang, Shou-Cheng
2008-01-01
We construct time reversal invariant topological superconductors and superfluids in two and three dimensions which are analogous to the recently discovered quantum spin Hall and three-d $Z_2$ topological insulators respectively. These states have a full pairing gap in the bulk, gapless counter-propagating Majorana states at the boundary, and a pair of Majorana zero modes associated with each vortex. We show that the time reversal symmetry naturally emerges as a supersymmetry, which changes th...
Holographic anyonic superfluidity
Jokela, Niko; Lifschytz, Gilad; Lippert, Matthew
2013-01-01
Starting with a holographic construction for a fractional quantum Hall state based on the D3-D7' system, we explore alternative quantization conditions for the bulk gauge fields. This gives a description of a quantum Hall state with various filling fractions. For a particular alternative quantization of the bulk gauge fields, we obtain a holographic anyon fluid in a vanishing background magnetic field. We show that this system is a superfluid, exhibiting the relevant gapless excitation.
Cooling with Superfluid Helium
Lebrun, P
2014-01-01
The technical properties of helium II (‘superfluid’ helium) are presented in view of its applications to the cooling of superconducting devices, particularly in particle accelerators. Cooling schemes are discussed in terms of heat transfer performance and limitations. Large-capacity refrigeration techniques below 2 K are reviewed, with regard to thermodynamic cycles as well as process machinery. Examples drawn from existing or planned projects illustrate the presentation. Keywords: superfluid helium, cryogenics
Thermodynamics of ultracold Fermi gases
International Nuclear Information System (INIS)
Complex Hamiltonians from condensed matter, such as the Fermi-Hubbard model, can be experimentally studied using ultracold gases. This thesis describes a new method for determining the equation of state of an ultracold gas, making the comparison with many-body theories straightforward. It is based on the measurement of the local pressure inside a trapped gas from the analysis of its in situ image. We first apply this method to the study of a Fermi gas with resonant interactions, a weakly-interacting 7Li gas acting as a thermometer. Surprisingly, none of the existing many-body theories of the unitary gas accounts for the equation of state deduced from our study over its full range. The virial expansion extracted from the high-temperature data agrees with the resolution of the three-body problem. At low temperature, we observe, contrary to some previous studies, that the normal phase behaves as a Fermi liquid. Finally we obtain the critical temperature for superfluidity from a clear signature on the equation of state. We also measure the pressure of the ground state as a function of spin imbalance and interaction strength - measure directly relevant to describe the crust of neutron stars. Our data validate Monte-Carlo simulations and quantify the Lee-Huang-Yang corrections to mean-field interactions in low-density fermionic or bosonic superfluids. We show that, in most cases, the partially polarized normal phase can be described as a Fermi liquid of polarons. The polaron effective mass extracted from the equation of state is in agreement with a study of collective modes. (author)
Low-lying excitations in a strongly interacting Fermi gas
Vale, Christopher; Hoinka, Sascha; Dyke, Paul; Lingham, Marcus
2016-05-01
We present measurements of the low-lying excitation spectrum of a strongly interacting Fermi gas across the Bardeen-Cooper-Schrieffer (BCS) to Bose-Einstein condensate (BEC) crossover using Bragg spectroscopy. By focussing the Bragg lasers onto the central volume of the cloud we can probe atoms at near-uniform density allowing measurement of the homogeneous density-density response function. The Bragg wavevector is set to be approximately half of the Fermi wavevector to probe the collective response. Below the superfluid transition temperature the Bragg spectra dominated by the Bogoliubov-Anderson phonon mode. Single particle excitations become visible at energies greater than twice the pairing gap. As interactions are tuned from the BCS to BEC regime the phonon and single particle modes separate apart and both the pairing gap and speed of sound can be directly read off in certain regions of the crossover. Single particle pair-breaking excitations become heavily suppressed as interactions are tuned from the BCS to BEC regimes.
Peng, Q. H.; Luo, Z. Q.
2005-01-01
Starting from a neutron star heating mechanism by the magnetic dipole radiation from the 3^P_2 neutron superfluid vortices in neutron stars, we propose a neutron phase oscillation model which describes the phase transition between the normal neutron Fermi fluid and the 3^P_2 neutron superfluid vortices at the transition temperature of T_{trans}=(5-6)\\times 10^8 K. With this model, we can give qualitative explanation to most of the pulsar glitches observed up to date.
Institute of Scientific and Technical Information of China (English)
Qiu-He Peng; Zhi-Quan Luo; Chih-Kang Chou
2006-01-01
Considering neutron star heating by magnetic dipole radiation from 3pF2 superfluid neutron vortices inside the star, we propose a neutron phase oscillation model between the normal neutron Fermi fluid and the 3pF2 superfluid neutron vortices at the transition temperature of Ttrans=(2-3)×108 K. With this model we can qualitatively explain most of the observations on pulsar glitches up to date.
Luttinger's theorem, superfluid vortices, and holography
Iqbal, Nabil
2011-01-01
Strongly coupled field theories with gravity duals can be placed at finite density in two ways: electric field flux emanating from behind a horizon, or bulk charged fields outside of the horizon that explicitly source the density. We discuss field-theoretical observables that are sensitive to this distinction. If the charged fields are fermionic, we discuss a modified Luttinger's theorem that holds for holographic systems, in which the sum of boundary theory Fermi surfaces counts only the charge outside of the horizon. If the charged fields are bosonic, we show that the the resulting superfluid phase may be characterized by the coefficient of the transverse Magnus force on a moving superfluid vortex, which again is sensitive only to the charge outside of the horizon. For holographic systems these observables provide a field-theoretical way to distinguish how much charge is held by a dual horizon, but they may be useful in more general contexts as measures of deconfined (i.e. "fractionalized") charge degrees o...
Symmetry-Protected Topological Superfluids and Superconductors —From the Basics to 3He—
Mizushima, Takeshi; Tsutsumi, Yasumasa; Kawakami, Takuto; Sato, Masatoshi; Ichioka, Masanori; Machida, Kazushige
2016-02-01
In this article, we give a comprehensive review of recent progress in research on symmetry-protected topological superfluids and topological crystalline superconductors, and their physical consequences such as helical and chiral Majorana fermions. We start this review article with the minimal model that captures the essence of such topological materials. The central part of this article is devoted to the superfluid 3He, which serves as a rich repository of novel topological quantum phenomena originating from the intertwining of symmetries and topologies. In particular, it is emphasized that the quantum fluid confined to nanofabricated geometries possesses multiple superfluid phases composed of the symmetry-protected topological superfluid B-phase, the A-phase as a Weyl superfluid, the nodal planar and polar phases, and the crystalline ordered stripe phase. All these phases generate noteworthy topological phenomena, including topological phase transitions concomitant with spontaneous symmetry breaking, Majorana fermions, Weyl superfluidity, emergent supersymmetry, spontaneous edge mass and spin currents, topological Fermi arcs, and exotic quasiparticles bound to topological defects. In relation to the mass current carried by gapless edge states, we also briefly review a longstanding issue on the intrinsic angular momentum paradox in 3He-A. Moreover, we share the current status of our knowledge on the topological aspects of unconventional superconductors, such as the heavy-fermion superconductor UPt3 and superconducting doped topological insulators, in connection with the superfluid 3He.
Metastability in spin polarised Fermi gases and quasiparticle decays
DEFF Research Database (Denmark)
Sadeghzadeh, Kayvan; Bruun, Georg; Lobo, Carlos;
2011-01-01
We investigate the metastability associated with the first order transition from normal to superfluid phases in the phase diagram of two-component polarised Fermi gases.We begin by detailing the dominant decay processes of single quasiparticles.Having determined the momentum thresholds of each pr...
Superfluidity within a small helium-4 cluster: the microscopic andronikashvili experiment
Grebenev; Toennies; Vilesov
1998-03-27
The infrared spectrum of single oxygen carbon sulfide (OCS) molecules was measured inside large superfluid pure helium-4 droplets and nonsuperfluid pure helium-3 droplets, both consisting of about 10(4) atoms. In the helium-4 droplets, sharp rotational lines were observed, whereas in helium-3 only a broad peak was found. This difference is interpreted as evidence that the narrow rotational lines, which imply free rotations, are a microscopic manifestation of superfluidity. Upon addition of 60 helium-4 atoms to the pure helium-3 droplets, the same sharp rotational lines were found; it appears that 60 is the minimum number needed for superfluidity. PMID:9516103
Hennigar, Robie A; Tjoa, Erickson
2016-01-01
We present what we believe is the first example of a "$\\lambda$-line" phase transition in black hole thermodynamics. This is a line of (continuous) second order phase transitions which in the case of liquid $^4$He marks the onset of superfluidity. The phase transition occurs for a class of asymptotically AdS hairy black holes in Lovelock gravity where a real scalar field is conformally coupled to gravity. We discuss the origin of this phase transition and outline the circumstances under which it (or generalizations of it) could occur.
International Nuclear Information System (INIS)
An analysis of previous theories of superfluidity of quantum solids is presented in relation to the nonclassical rotational moment of inertia (NCRM) found first in Kim and Chan experiments. A theory of supersolidity is proposed based on the presence of an additional conservation law. It is shown that the additional entropy or mass fluxes depend on the quasiparticle dispersion relation and vanish in the effective mass approximation. This implies that at low temperatures when the parabolic part of the dispersion relation predominates the supersolid properties should be less expressed. (author)
Ultracold Fermi gases: from Bose-Einstein condensation of molecules to Cooper pairs
International Nuclear Information System (INIS)
Full text: We will describe recent experiments aiming at studying superfluidity in ultra-cold Fermi gases. Because of the Pauli exclusion principle, cooling methods and analysis techniques developed for bosons must be modified for fermions. Thanks to a resonance phenomenon in ultra-cold collisions, it is possible to adjust the sign and magnitude of the effective interaction between trapped fermions and to enter into the strongly correlated regime. Taking advantage of this tunability of interactions, it has been possible to produce Bose-Einstein condensates (BEC) of molecules and to study some of their properties. We will then present data recorded in the crossover region between BEC of molecules and the BCS regime of fermions with weak attractive interaction. Finally a few perspectives for this work at the interface between atomic physics and condensed matter physics will be given. (author)
Merritt, J M; Miller, R E; K\\"upper, Jochen; Merritt, Jeremy M.; Miller, Roger E.
2006-01-01
Rotationally resolved infrared spectra are reported for the X-HCN (X = Cl, Br, I) binary complexes solvated in helium nanodroplets. These results are directly compared with that obtained previously for the corresponding X-HF complexes [J. M. Merritt, J. K\\"upper, and R. E. Miller, PCCP, 7, 67 (2005)]. For bromine and iodine atoms complexed with HCN, two linear structures are observed and assigned to the $^{2}\\Sigma_{1/2}$ and $^{2}\\Pi_{3/2}$ ground electronic states of the nitrogen and hydrogen bound geometries, respectively. Experiments for HCN + chlorine atoms give rise to only a single band which is attributed to the nitrogen bound isomer. That the hydrogen bound isomer is not stabilized is rationalized in terms of a lowering of the isomerization barrier by spin-orbit coupling. Theoretical calculations with and without spin-orbit coupling have also been performed and are compared with our experimental results. The possibility of stabilizing high-energy structures containing multiple radicals is discussed, ...
Nambu-Goldstone Fermion Mode in Quark-Gluon Plasma and Bose-Fermi Cold Atom System
International Nuclear Information System (INIS)
It was suggested that supersymmetry (SUSY) is broken at finite temperature, and as a result of the symmetry breaking, a Nambu-Goldstone fermion (goldstino) related to SUSY breaking appears. Since dispersion relations of quarks and gluons are almost degenerate at extremely high temperature, quasi-zero energy quark excitation was suggested to exist in quark-gluon plasma (QGP), though QCD does not have exact SUSY. On the other hand, in condensed matter system, a setup of cold atom system in which the Hamiltonian has SUSY was proposed, the goldstino was suggested to exist, and the dispersion relation of that mode at zero temperature was obtained recently. In this presentation, we obtain the expressions for the dispersion relation of the goldstino in cold atom system at finite temperature, and compare it with the dispersion of the quasi zero-mode in QGP. Furthermore, we show that the form of the dispersion relation of the goldstino can be understood by using an analogy with a magnon in ferromagnet. We also discuss on how the dispersion relation of the goldstino is reflected in observable quantities in experiment. (author)
International Nuclear Information System (INIS)
We report on the first simultaneous observations that cover the optical, X-ray, and high-energy gamma-ray bands of the BL Lac object PKS 2155-304. The gamma-ray bands were observed for 11 days, between 2008 August 25 and 2008 September 6 (MJD 54704-54715), jointly with the Fermi Gamma-ray Space Telescope and the HESS atmospheric Cherenkov array, providing the first simultaneous MeV-TeV spectral energy distribution (SED) with the new generation of γ-ray telescopes. The ATOM telescope and the RXTE and Swift observatories provided optical and X-ray coverage of the low-energy component over the same time period. The object was close to the lowest archival X-ray and very high energy (VHE; >100 GeV) state, whereas the optical flux was much higher. The light curves show relatively little (∼30%) variability overall when compared to past flaring episodes, but we find a clear optical/VHE correlation and evidence for a correlation of the X-rays with the high-energy spectral index. Contrary to previous observations in the flaring state, we do not find any correlation between the X-ray and VHE components. Although synchrotron self-Compton models are often invoked to explain the SEDs of BL Lac objects, the most common versions of these models are at odds with the correlated variability we find in the various bands for PKS 2155-304.
Energy Technology Data Exchange (ETDEWEB)
Aharonian, F.; /Heidelberg, Max Planck Inst. /Dublin Inst.; Akhperjanian, A.G.; /Yerevan Phys. Inst.; Anton, G.; /Erlangen - Nuremberg U.; Barres de Almeida, U.; /Durham U.; Bazer-Bachi, A.R.; /Toulouse, CESR; Becherini, Y.; /APC, Paris; Behera, B.; /Heidelberg Observ.; Bernlohr, K.; /Heidelberg, Max Planck Inst. /Humboldt U., Berlin; Boisson, C.; /LUTH, Meudon; Bochow, A.; /Heidelberg, Max Planck Inst.; Borrel, V.; /Toulouse, CESR; Brion, E.; /DAPNIA, Saclay; Brucker, J.; /Erlangen - Nuremberg U.; Brun, P.; /DAPNIA, Saclay; Buhler, R.; /Heidelberg, Max Planck Inst.; Bulik, T.; /Warsaw, Copernicus Astron. Ctr.; Busching, I.; /Western Ontario U.; Boutelier, T.; /Grenoble Observ.; Chadwick, P.M.; /Durham U.; Charbonnier, A.; /Paris U., VI-VII; Chaves, R.C.G.; /Heidelberg, Max Planck Inst. /Durham U. /Ecole Polytechnique /Heidelberg, Max Planck Inst. /Annecy, LAPP /Humboldt U., Berlin /Durham U. /Namibia U. /Western Ontario U. /Ecole Polytechnique /Heidelberg, Max Planck Inst. /Durham U. /APC, Paris /Heidelberg, Max Planck Inst. /Dublin Inst. /Annecy, LAPP /Grenoble Observ. /Warsaw, Copernicus Astron. Ctr. /Cracow, INP /Heidelberg, Max Planck Inst. /Heidelberg Observ. /APC, Paris /Montpellier U. /Montpellier U. /Montpellier U. /Heidelberg, Max Planck Inst. /Ecole Polytechnique /Humboldt U., Berlin /Dublin Inst. /Montpellier U. /APC, Paris /SLAC; /more authors..
2009-05-07
We report on the first simultaneous observations that cover the optical, X-ray, and high-energy gamma-ray bands of the BL Lac object PKS 2155-304. The gamma-ray bands were observed for 11 days, between 2008 August 25 and 2008 September 6 (MJD 54704-54715), jointly with the Fermi Gamma-ray Space Telescope and the HESS atmospheric Cherenkov array, providing the first simultaneous MeV-TeV spectral energy distribution (SED) with the new generation of {gamma}-ray telescopes. The ATOM telescope and the RXTE and Swift observatories provided optical and X-ray coverage of the low-energy component over the same time period. The object was close to the lowest archival X-ray and very high energy (VHE; >100 GeV) state, whereas the optical flux was much higher. The light curves show relatively little ({approx}30%) variability overall when compared to past flaring episodes, but we find a clear optical/VHE correlation and evidence for a correlation of the X-rays with the high-energy spectral index. Contrary to previous observations in the flaring state, we do not find any correlation between the X-ray and VHE components. Although synchrotron self-Compton models are often invoked to explain the SEDs of BL Lac objects, the most common versions of these models are at odds with the correlated variability we find in the various bands for PKS 2155-304.
Raja, Muhammad Asif Zahoor; Zameer, Aneela; Khan, Aziz Ullah; Wazwaz, Abdul Majid
2016-01-01
In this study, a novel bio-inspired computing approach is developed to analyze the dynamics of nonlinear singular Thomas-Fermi equation (TFE) arising in potential and charge density models of an atom by exploiting the strength of finite difference scheme (FDS) for discretization and optimization through genetic algorithms (GAs) hybrid with sequential quadratic programming. The FDS procedures are used to transform the TFE differential equations into a system of nonlinear equations. A fitness function is constructed based on the residual error of constituent equations in the mean square sense and is formulated as the minimization problem. Optimization of parameters for the system is carried out with GAs, used as a tool for viable global search integrated with SQP algorithm for rapid refinement of the results. The design scheme is applied to solve TFE for five different scenarios by taking various step sizes and different input intervals. Comparison of the proposed results with the state of the art numerical and analytical solutions reveals that the worth of our scheme in terms of accuracy and convergence. The reliability and effectiveness of the proposed scheme are validated through consistently getting optimal values of statistical performance indices calculated for a sufficiently large number of independent runs to establish its significance. PMID:27610319
Phase Diagram of Two-dimensional Polarized Fermi Gas With Spin-Orbit Coupling
Yang, Xiaosen; Wan, Shaolong
2011-01-01
We investigate the ground state of the two-dimensional polarized Fermi gas with spin-orbit coupling and construct the phase diagram at zero temperature. We find there exist phase separation when the binding energy is low. As the binding energy increasing, the topological nontrivial superfluid phase coexist with topologically trivial superfluid phase which is topological phase separation. The spin-orbit coupling interaction enhance the triplet pairing and destabilize the phase separation again...
Crossover from BCS superconductivity to superfluidity of local pairs
International Nuclear Information System (INIS)
We review some recent results concerning crossover from cooperative Cooper pairing to independent bound states formation and their superfluidity, and a possible relevance of the crossover behavior to the anomalous properties of short-coherence length superconductors. Using the extended Hubbard model with on-site attraction (EHM), we analyze the behavior of collective modes, thermodynamic and electromagnetic properties versus the coupling strength and electron concentration. The normal state properties of the 2D attractive Hubbard model obtained with the conserving, self-consistent T-matrix approach, are presented. These studies also indicate possible deviations from conventional Fermi-liquid behavior, above Tc, in 2D short coherence length superconductors. (orig.)
Lifshitz Superfluid Hydrodynamics
Chapman, Shira; Oz, Yaron
2014-01-01
We construct the first order hydrodynamics of quantum critical points with Lifshitz scaling and a spontaneously broken symmetry. The fluid is described by a combination of two flows, a normal component that carries entropy and a super-flow which has zero viscosity and carries no entropy. We analyze the new transport effects allowed by the lack of boost invariance and constrain them by the local second law of thermodynamics. Imposing time-reversal invariance, we find eight new parity even transport coefficients. The formulation is applicable, in general, to any superfluid/superconductor with an explicit breaking of boost symmetry, in particular to high $T_c$ superconductors. We discuss possible experimental signatures.
Superfluid Fermi Gases in a Rotating Anharmonic Trap
Institute of Scientific and Technical Information of China (English)
MA Juan; XUE Ju-Kui
2011-01-01
The quadrupole mode frequency, the monopole mode frequency, and the critical rotational frequency for stirring a single vortex nucleation along the BEC-BCS crossover are obtained. The results show that, in a rotating anisotropic anharmonic trap, the quadrupole mode frequency and the critical rotational frequency for stirring a single vortex nucleation are modified significantly when the system crosses from the BEC side to the BCS side: the anisotropy of the trap induces a downshift of the quadrupole mode frequency and the critical rotational frequency and helps the vortex formation in the system, while an anharmonic trap induces an upshift of the quadrupole mode frequency and the critical rotational frequency and suppresses the vortex formation in the system.
Relativistic superfluidity and vorticity from the nonlinear Klein-Gordon equation
Xiong, Chi; Guo, Yulong; Liu, Xiaopei; Huang, Kerson
2014-01-01
We investigate superfluidity, and the mechanism for creation of quantized vortices, in the relativistic regime. The general framework is a nonlinear Klein-Gordon equation in curved spacetime for a complex scalar field, whose phase dynamics gives rise to superfluidity. The mechanisms discussed are local inertial forces (Coriolis and centrifugal), and current-current interaction with an external source. The primary application is to cosmology, but we also discuss the reduction to the non-relativistic nonlinear Schr\\"{o}dinger equation, which is widely used in describing superfluidity and vorticity in liquid helium and cold-trapped atomic gases.
Thermohydraulics of a horizontal diphasic flow of superfluid helium
International Nuclear Information System (INIS)
This study aims at characterizing helium two phase flows, and to identify the dependence of their characteristics on various thermo-hydraulic parameters: vapour velocity, liquid height, vapour density, specificities of superfluidity. Both the engineer and the physicist's points of view are taken into consideration: the first one in terms of optimization of a particular cooling scheme based on a two-phase flow, and these second one in terms of more fundamental atomization-related questions. It has been shown that for velocities around 3 to 4 m/s, the liquid phase that was initially stratified undergoes an atomization through the presence of a drop haze carried by the vapor phase.This happens for superfluid helium as well as for normal helium without main differences on atomization
International Nuclear Information System (INIS)
Superfluidity and phase separation in 3He-4He mixtures immersed in aerogel are studied by renormalization-group theory. The quenched disorder imposed by aerogel, both at the atomic level and at the geometric level, is included. The calculation is conducted via the coupled renormalization-group mappings, near and away from aerogel, of the quenched probability distributions of random interactions. Random-bond effects on the onset of superfluidity and random-field effects on superfluid-superfluid phase separation are seen. The quenched randomness causes the λ line of second-order phase transitions of superfluidity onset to reach zero temperature, in agreement with general predictions and experiments. The effects of the atomic and geometric randomness of aerogel are investigated separately and jointly. copyright 1997 The American Physical Society
Energy Technology Data Exchange (ETDEWEB)
Erika Bailey
2011-10-27
The Enrico Fermi Atomic Power Plant, Unit 1 (Fermi 1) was a fast breeder reactor design that was cooled by sodium and operated at essentially atmospheric pressure. On May 10, 1963, the Atomic Energy Commission (AEC) granted an operating license, DPR-9, to the Power Reactor Development Company (PRDC), a consortium specifically formed to own and operate a nuclear reactor at the Fermi 1 site. The reactor was designed for a maximum capability of 430 megawatts (MW); however, the maximum reactor power with the first core loading (Core A) was 200 MW. The primary system was filled with sodium in December 1960 and criticality was achieved in August 1963. The reactor was tested at low power during the first couple years of operation. Power ascension testing above 1 MW commenced in December 1965 immediately following the receipt of a high-power operating license. In October 1966 during power ascension, zirconium plates at the bottom of the reactor vessel became loose and blocked sodium coolant flow to some fuel subassemblies. Two subassemblies started to melt and the reactor was manually shut down. No abnormal releases to the environment occurred. Forty-two months later after the cause had been determined, cleanup completed, and the fuel replaced, Fermi 1 was restarted. However, in November 1972, PRDC made the decision to decommission Fermi 1 as the core was approaching its burn-up limit. The fuel and blanket subassemblies were shipped off-site in 1973. Following that, the secondary sodium system was drained and sent off-site. The radioactive primary sodium was stored on-site in storage tanks and 55 gallon (gal) drums until it was shipped off-site in 1984. The initial decommissioning of Fermi 1 was completed in 1975. Effective January 23, 1976, DPR-9 was transferred to the Detroit Edison Company (DTE) as a 'possession only' license (DTE 2010a). This report details the confirmatory activities performed during the second Oak Ridge Institute for Science and Education
Bouffard, Karen
1999-05-01
This column contains problems and solutions for the general category of questions known as "Fermi" questions. Forcing the students to use their ability to estimate, giving answers in terms of order-of-magnitude, is not only a challenge for a competition, but a teaching strategy to use in the classroom to develop self-confidence and the ability to analyze answers as to whether or not they make sense, as opposed to relying on the "precision" of a calculator value.
Hierarchic Models of Turbulence, Superfluidity and Superconductivity
Kaivarainen, Alex
2000-01-01
New models of Turbulence, Superfluidity and Superconductivity, based on new Hierarchic theory, general for liquids and solids (physics/0102086), have been proposed. CONTENTS: 1 Turbulence. General description; 2 Mesoscopic mechanism of turbulence; 3 Superfluidity. General description; 4 Mesoscopic scenario of fluidity; 5 Superfluidity as a hierarchic self-organization process; 6 Superfluidity in 3He; 7 Superconductivity: General properties of metals and semiconductors; Plasma oscillations; Cy...
Microscopic theory of sound propagation in the superfluid 3He-aerogel system
International Nuclear Information System (INIS)
We present a theory of sound propagation in superfluid 3He confined in aerogel, taking dragged aerogel motion into account. The superfluid dynamics coupled with the aerogel motion is formulated by use of the Keldysh Green's function for weak-coupling superfluid Fermi liquid. We apply the theory to the hydrodynamic regime and calculate the attenuation of a hydrodynamic longitudinal sound mode, the so-called fast mode. The result is compared to the acoustic experiment reported by the Northwestern University group [R. Nomura, G. Gervais, T. M. Haard, Y. Lee, N. Mulders, and W. P. Halperin, Phys. Rev. Lett. 85, 4325 (2000); G. Gervais, R. Nomura, T. M. Haard, Y. Lee, N. Mulders, and W. P. Halperin, J. Low Temp. Phys. 122, 1 (2001)]. We find reasonable agreement between the theory and the experiment
Enrico Fermi the obedient genius
Bruzzaniti, Giuseppe
2016-01-01
This biography explores the life and career of the Italian physicist Enrico Fermi, which is also the story of thirty years that transformed physics and forever changed our understanding of matter and the universe: nuclear physics and elementary particle physics were born, nuclear fission was discovered, the Manhattan Project was developed, the atomic bombs were dropped, and the era of “big science” began. It would be impossible to capture the full essence of this revolutionary period without first understanding Fermi, without whom it would not have been possible. Enrico Fermi: The Obedient Genius attempts to shed light on all aspects of Fermi’s life - his work, motivation, influences, achievements, and personal thoughts - beginning with the publication of his first paper in 1921 through his death in 1954. During this time, Fermi demonstrated that he was indeed following in the footsteps of Galileo, excelling in his work both theoretically and experimentally by deepening our understanding of the Pauli e...
Rotating a Rashba-coupled Fermi gas in two dimensions
Doko, E.; Subaşı, A. L.; Iskin, M.
2016-03-01
We analyze the interplay of adiabatic rotation and Rashba spin-orbit coupling on the BCS-BEC evolution of a harmonically trapped Fermi gas in two dimensions under the assumption that vortices are not excited. First, by taking the trapping potential into account via both the semiclassical and exact quantum-mechanical approaches, we firmly establish the parameter regime where the noninteracting gas forms a ring-shaped annulus. Then, by taking the interactions into account via the BCS mean-field approximation, we study the pair-breaking mechanism that is induced by rotation, i.e., the Coriolis effects. In particular, we show that the interplay allows for the possibility of creating either an isolated annulus of rigidly rotating normal particles that is disconnected from the central core of nonrotating superfluid pairs or an intermediate mediator phase where the superfluid pairs and normal particles coexist as a partially rotating gapless superfluid.
International Nuclear Information System (INIS)
In order to explore a possibility of superfluidity in confined strongly-correlated fermion systems, e.g., nano-scale cuprate High-Tc superconductors and atomic Fermi gases loaded on optical lattice, we implement an exact diagonalization code for their mathematical model, i.e., a trapped Hubbard model on the Earth Simulator. We compare two diagonalization algorithms, the traditional Lanczos method and a new algorithm, the preconditioned conjugate gradient (PCG) method, and find that when using the PCG the total CPU time can be reduced to 1/3 - 1/5 compared to the former one since the convergence can be dramatically improved by choosing a good preconditioner and the communication overhead is much more efficiently concealed in the PCG method. Consequently, such a performance improvement enables us to do systematic studies for several parameters. Numerical simulation results reveal that an unconventional type of pairing specific to the confined system, which may cause superfluidity, develops under a strong repulsive interaction. (author)
Dynamics of vortex assisted metal condensation in superfluid helium.
Popov, Evgeny; Mammetkuliyev, Muhammet; Eloranta, Jussi
2013-05-28
Laser ablation of copper and silver targets immersed in bulk normal and superfluid (4)He was studied through time-resolved shadowgraph photography. In normal fluid, only a sub-millimeter cavitation bubble is created and immediate formation of metal clusters is observed within a few hundred microseconds. The metal clusters remain spatially tightly focused up to 15 ms, and it is proposed that this observation may find applications in particle image velocimetry. In superfluid helium, the cavitation bubble formation process is distinctly different from the normal fluid. Due to the high thermal conductivity and an apparent lag in the breakdown of superfluidity, about 20% of the laser pulse energy was transferred directly into the liquid and a large gas bubble, up to several millimeters depending on laser pulse energy, is created. The internal temperature of the gas bubble is estimated to exceed 9 K and the following bubble cool down period therefore includes two separate phase transitions: gas-normal liquid and normal liquid-superfluid. The last stage of the cool down process was assigned to the superfluid lambda transition where a sudden formation of large metal clusters is observed. This is attributed to high vorticity created in the volume where the gas bubble previously resided. As shown by theoretical bosonic density functional theory calculations, quantized vortices can trap atoms and dimers efficiently, exhibiting static binding energies up to 22 K. This, combined with hydrodynamic Bernoulli attraction, yields total binding energies as high as 35 K. For larger clusters, the static binding energy increases as a function of the volume occupied in the liquid to minimize the surface tension energy. For heliophobic species an energy barrier develops as a function of the cluster size, whereas heliophilics show barrierless entry into vortices. The present theoretical and experimental observations are used to rationalize the previously reported metal nanowire assembly in
Dynamics of vortex assisted metal condensation in superfluid helium
Popov, Evgeny; Mammetkuliyev, Muhammet; Eloranta, Jussi
2013-05-01
Laser ablation of copper and silver targets immersed in bulk normal and superfluid 4He was studied through time-resolved shadowgraph photography. In normal fluid, only a sub-millimeter cavitation bubble is created and immediate formation of metal clusters is observed within a few hundred microseconds. The metal clusters remain spatially tightly focused up to 15 ms, and it is proposed that this observation may find applications in particle image velocimetry. In superfluid helium, the cavitation bubble formation process is distinctly different from the normal fluid. Due to the high thermal conductivity and an apparent lag in the breakdown of superfluidity, about 20% of the laser pulse energy was transferred directly into the liquid and a large gas bubble, up to several millimeters depending on laser pulse energy, is created. The internal temperature of the gas bubble is estimated to exceed 9 K and the following bubble cool down period therefore includes two separate phase transitions: gas-normal liquid and normal liquid-superfluid. The last stage of the cool down process was assigned to the superfluid lambda transition where a sudden formation of large metal clusters is observed. This is attributed to high vorticity created in the volume where the gas bubble previously resided. As shown by theoretical bosonic density functional theory calculations, quantized vortices can trap atoms and dimers efficiently, exhibiting static binding energies up to 22 K. This, combined with hydrodynamic Bernoulli attraction, yields total binding energies as high as 35 K. For larger clusters, the static binding energy increases as a function of the volume occupied in the liquid to minimize the surface tension energy. For heliophobic species an energy barrier develops as a function of the cluster size, whereas heliophilics show barrierless entry into vortices. The present theoretical and experimental observations are used to rationalize the previously reported metal nanowire assembly in
Role of nucleonic Fermi surface depletion in neutron star cooling
Dong, J M; Zhang, H F; Zuo, W
2015-01-01
The Fermi surface depletion of beta-stable nuclear matter is calculated to study its effects on several physical properties which determine the neutron star thermal evolution. The neutron and proton Z factors measuring the corresponding Fermi surface depletions, are calculated within the Brueckner-Hartree-Fock approach employing the AV18 two-body force supplemented by a microscopic three body force. Neutrino emissivity, heat capacity and, in particular, neutron 3PF2 superfluidity turn out to be reduced, especially at high baryonic density, to such an extent that the cooling rates of young neutron stars are significantly slowed
Two definitions of superfluid density
International Nuclear Information System (INIS)
We point out that two different definitions of the superfluid density - through statistical response to static gauge phase and through dynamic response to altering gauge phase - yield, generally speaking, different quantities in d<3. The physics leading to this difference is associated with the equilibrium statistics of supercurrent states. Some experimentally observable consequences of this fact are discussed
Scale invariance and superfluid turbulence
Energy Technology Data Exchange (ETDEWEB)
Sen, Siddhartha, E-mail: siddhartha.sen@tcd.ie [CRANN, Trinity College Dublin, Dublin 2 (Ireland); R.K. Mission Vivekananda University, Belur 711 202, West Bengal (India); Ray, Koushik, E-mail: koushik@iacs.res.in [Department of Theoretical Physics, Indian Association for the Cultivation of Science, Calcutta 700 032 (India)
2013-11-11
We construct a Schroedinger field theory invariant under local spatial scaling. It is shown to provide an effective theory of superfluid turbulence by deriving, analytically, the observed Kolmogorov 5/3 law and to lead to a Biot–Savart interaction between the observed filament excitations of the system as well.
Experimental studies of spin-imbalanced Fermi gases in 2D geometries
Thomas, John
We study the thermodynamics of a quasi-two-dimensional Fermi gas, which is not quite two-dimensional (2D), but far from three dimensional (3D). This system offers opportunities to test predictions that cross interdisciplinary boundaries, such as enhanced superfluid transition temperatures in spin-imbalanced quasi-2D superconductors, and provides important benchmarks for calculations of the phase diagrams. In the experiments, an ultra-cold Fermi gas is confined in an infrared CO2 laser standing-wave, which produces periodic pancake-shaped potential wells, separated by 5.3 μm. To study the thermodynamics, we load an ultra-cold mixture of N1 = 800 spin 1/2 -up and N2 measured properties are in disagreement with 2D-BCS theory, but can be fit by a 2D-polaron gas model, where each atom is surrounded by a cloud of particle-hole pairs of the opposite spin. However, this model fails to predict a transition to a spin-balanced central region as N2/N1is increased. Supported by the physics divisions of ARO, AFOSR, and NSF and by the Division of Materials Science and Engineering, the Office of Basic Energy Sciences, DOE.
Coordinate-Space Hartree-Fock-Bogoliubov Solvers for Super fluid Fermi Systems in Large Boxes
Pei, J. C.; Fann, G. I.; Harrison, R. J.; Nazarewicz, W.; Hill, J.; Galindo, D.; Jia, J.
2012-12-01
The self-consistent Hartree-Fock-Bogoliubov problem in large boxes can be solved accurately in the coordinate space with the recently developed solvers HFB-AX (2D) and MADNESS-HFB (3D). This is essential for the description of superfluid Fermi systems with complicated topologies and significant spatial extend, such as fissioning nuclei, weakly-bound nuclei, nuclear matter in the neutron star rust, and ultracold Fermi atoms in elongated traps. The HFB-AX solver based on B-spline techniques uses a hybrid MPI and OpenMP programming model for parallel computation for distributed parallel computation, within a node multi-threaded LAPACK and BLAS libraries are used to further enable parallel calculations of large eigensystems. The MADNESS-HFB solver uses a novel multi-resolution analysis based adaptive pseudo-spectral techniques to enable fully parallel 3D calculations of very large systems. In this work we present benchmark results for HFB-AX and MADNESS-HFB on ultracold trapped fermions.
Coordinate-Space Hartree-Fock-Bogoliubov Solvers for Super fluid Fermi Systems in Large Boxes
International Nuclear Information System (INIS)
The self-consistent Hartree-Fock-Bogoliubov problem in large boxes can be solved accurately in the coordinate space with the recently developed solvers HFB-AX (2D) and MADNESS-HFB (3D). This is essential for the description of superfluid Fermi systems with complicated topologies and significant spatial extend, such as fissioning nuclei, weakly-bound nuclei, nuclear matter in the neutron star rust, and ultracold Fermi atoms in elongated traps. The HFB-AX solver based on B-spline techniques uses a hybrid MPI and OpenMP programming model for parallel computation for distributed parallel computation, within a node multi-threaded LAPACK and BLAS libraries are used to further enable parallel calculations of large eigensystems. The MADNESS-HFB solver uses a novel multi-resolution analysis based adaptive pseudo-spectral techniques to enable fully parallel 3D calculations of very large systems. In this work we present benchmark results for HFB-AX and MADNESS-HFB on ultracold trapped fermions.
International Nuclear Information System (INIS)
A human factors audit of the Fermi-2 control room was conducted April 27 through May 1, 1981. This report contains the audit team findings, organized according to the draft NUREG-0700 guidelines sections. The discrepancies identified during the audit are categorized according to their severity and the required schedule for their resolution
International Nuclear Information System (INIS)
The visualization of chiral p-wave superfluidity in Fermi gases near p-wave Feshbach resonances is theoretically examined. It is proposed that the superfluidity becomes detectable in the entire BCS-BEC regimes through (i) vortex visualization by the density depletion inside the vortex core and (ii) intrinsic angular momentum in vortex-free states. It is revealed that both (i) and (ii) are closely connected with the Majorana zero energy mode of the vortex core and the edge mode, which survive until the strong coupling BCS regime is approached from the weak coupling limit and vanish in the Bose-Einstein condensation regime
Novel sound phenomena in superfluid helium in aerogel and other impure superfluids
International Nuclear Information System (INIS)
During the last decade new techniques for producing impure superfluids with unique properties have been developed. This new class of systems includes superfluid helium confined to aerogel, HeII with different impurities (D2, N2, Ne, Kr), superfluids in Vycor glasses, and watergel. These systems exhibit very unusual properties including unexpected acoustic features. We discuss the sound properties of these systems and show that sound phenomena in impure superfluids are modified from those in pure superfluids. We calculate the coupling between temperature and pressure oscillations for impure superfluids and for superfluid He in aerogel. We show that the coupling between these two sound modes is governed either by c∂ρ/∂c or σρaρs (for aerogel) rather than thermal expansion coefficient ∂ρ/∂T, which is enormously small in pure superfluids. This replacement plays a fundamental role in all sound phenomena in impure superfluids. It enhances the coupling between the two sound modes that leads to the existence of such phenomena as the slow mode and heat pulse propagation with the velocity of first sound observed in superfluids in aerogel. This means that it is possible to observe in impure superfluids such unusual sound phenomena as slow pressure (density) waves and fast temperature (entropy) waves. The enhancement of the coupling between the two sound modes decreases the threshold values for nonlinear processes as compared to pure superfluids. Sound conversion, which has been observed in pure superfluids only by shock waves should be observed at moderate sound amplitude in impure superfluids. Cerenkov emission of second sound by first sound (which never been observed in pure superfluids) could be observed in impure superfluids
When Do Superfluidity and Long Range Order Imply Entanglement?
Vedral, V
2007-01-01
We investigate tacitly assumed relationships between the concepts of super-fluidity (-conductivity), long range order and entanglement. We prove that the three are by no means equivalent, but that notwithstanding, some rigorous implication can be established between them. This leads to three different, albeit frequently related, notions of "criticality", all of which are exemplified within the Hubbard model in the low density regime. We use Peierls' method of twisted Hamiltonians to link the existence of entanglement to superfluidity and (quasi)-long range order. As an application of our formalism, we show that recent experiments with cold atoms already prove the existence of the field theoretic, spatial entanglement in two dimensions. More interestingly, the appearance of entanglement in these experiments seems to be intimately related to the phase transition of the Kosterlitz Thouless type.
Relativistic superfluid hydrodynamics from field theory
Alford, Mark G; Schmitt, Andreas; Stetina, Stephan
2012-01-01
It is well known that the hydrodynamics of a zero-temperature superfluid can be formulated in field-theoretic terms, relating for example the superfluid four-velocity to the gradient of the phase of a Bose-condensed scalar field. At nonzero temperatures, where the phenomenology of a superfluid is usually described within a two-fluid picture, this relationship is less obvious. For the case of a uniform, dissipationless superfluid at small temperatures and weak coupling we discuss this relationship within a phi^4 model. For instance, we compute the entrainment coefficient, which describes the interaction between the superfluid and the normal-fluid components, and the velocities of first and second sound in the presence of a superflow. Our study is very general, but can also be seen as a step towards understanding the superfluid properties of various phases of dense nuclear and quark matter in the interior of compact stars.
Hierarchic Models of Turbulence, Superfluidity and Superconductivity
Kaivarainen, A
2000-01-01
New models of Turbulence, Superfluidity and Superconductivity, based on new Hierarchic theory, general for liquids and solids (physics/0102086), have been proposed. CONTENTS: 1 Turbulence. General description; 2 Mesoscopic mechanism of turbulence; 3 Superfluidity. General description; 4 Mesoscopic scenario of fluidity; 5 Superfluidity as a hierarchic self-organization process; 6 Superfluidity in 3He; 7 Superconductivity: General properties of metals and semiconductors; Plasma oscillations; Cyclotron resonance; Electroconductivity; 8. Microscopic theory of superconductivity (BCS); 9. Mesoscopic scenario of superconductivity: Interpretation of experimental data in the framework of mesoscopic model of superconductivity.
Microphotonic Forces From Superfluid Flow
McAuslan, D. L.; Harris, G. I.; Baker, C; Sachkou, Y.; He, X; Sheridan, E.; Bowen, W. P.
2015-01-01
In cavity optomechanics, radiation pressure and photothermal forces are widely utilized to cool and control micromechanical motion, with applications ranging from precision sensing and quantum information to fundamental science. Here, we realize an alternative approach to optical forcing based on superfluid flow and evaporation in response to optical heating. We demonstrate optical forcing of the motion of a cryogenic microtoroidal resonator at a level of 1.46 nN, roughly one order of magnitu...
Rotons, Superfluidity, and Helium Crystals
International Nuclear Information System (INIS)
Fritz London understood that quantum mechanics could show up at the macroscopic level, and, in 1938, he proposed that superfluidity was a consequence of Bose-Einstein condensation. However, Lev Landau never believed in London's ideas; instead, he introduced quasiparticles to explain the thermodynamics of superfluid 4He and a possible mechanism for its critical velocity. One of these quasiparticles, a crucial one, was his famous ''roton'' which he considered as an elementary vortex. At the LT0 conference (Cambridge, 1946), London criticized Landau and his ''theory based on the shaky grounds of imaginary rotons''. Despite their rather strong disagreement, Landau was awarded the London prize in 1960, six years after London's death. Today, we know that London and Landau had both found part of the truth: BEC takes place in 4He, and rotons exist.In my early experiments on quantum evaporation, I found direct evidence for the existence of rotons and for evaporation processes in which they play the role of photons in the photoelectric effect. But rotons are now considered as particular phonons which are nearly soft, due to some local order in superfluid 4He. Later we studied helium crystals which are model systems for the general study of crystal surfaces, but also exceptional systems with unique quantum properties. In our recent studies of nucleation, rotons show their importance again: by using acoustic techniques, we have extended the study of liquid 4He up to very high pressures where the liquid state is metastable, and we wish to demonstrate that the vanishing of the roton gap may destroy superfluidity and trigger an instability towards the crystalline state
Acoustic streaming in superfluid helium
International Nuclear Information System (INIS)
Quantitative measurements of acoustic streaming velocity in liquid helium as a function of sound intensity (up to the cavitation threshold), frequency (1, 3, and 10 MHz), and temperature (1.43 K< or =T< or =2.19 K) are reported. A transition to superfluid turbulence, several flow regions and flow fluctuations are observed. Comparison with the predictions of the second-order Khalatnikov two- fluid hydrodynamic equations indicates good functional and quantitative agreement
Renormalization group analysis of order parameter fluctuations in fermionic superfluids
International Nuclear Information System (INIS)
In this work fluctuation effects in two interacting fermion systems exhibiting fermionic s-wave superfluidity are analyzed with a modern renormalization group method. A description in terms of a fermion-boson theory allows an investigation of order parameter fluctuations already on the one-loop level. In the first project a quantum phase transition between a semimetal and a s-wave superfluid in a Dirac cone model is studied. The interplay between fermions and quantum critical fluctuations close to and at the quantum critical point at zero and finite temperatures are studied within a coupled fermion-boson theory. At the quantum critical point non-Fermi liquid and non-Gaussian behaviour emerge. Close to criticality several quantities as the susceptibility show a power law behaviour with critical exponents. We find an infinite correlation length in the entire semimetallic ground state also away from the quantum critical point. In the second project, the ground state of an s-wave fermionic superfluid is investigated. Here, the mutual interplay between fermions and order parameter fluctuations is studied, especially the impact of massless Goldstone fluctuations, which occur due to spontaneous breaking of the continuous U(1)-symmetry. Fermionic gap and bosonic order parameter are distinguished. Furthermore, the bosonic order parameter is decomposed in transverse and longitudinal fluctuations. The mixing between transverse and longitudinal fluctuations is included in our description. Within a simple truncation of the fermion-boson RG flow, we describe the fermion-boson theory for the first time in a consistent manner. Several singularities appear due the Goldstone fluctuations, which partially cancel due to symmetry. Our RG flow captures the correct infrared asymptotics of the system, where the collective excitations act as an interacting Bose gas. Lowest order Ward identities and the massless Goldstone mode are fulfilled in our truncation.
On the semiclassical description of nuclear Fermi liquid drops
International Nuclear Information System (INIS)
In this series of lectures we aimed at presenting a self-contained semiclassical theory entirely based on the extended Thomas-Fermi or Wigner-Kirkwood h expansion in phase space. We saw that not only the Wigner transform of the single particle density matrix can be understood and very accurately represented in this way but that also generalisations to correlation functions are straightforward. First, we demonstrated a generalisation to superfluid nuclei and to superfluid nuclei in slow rotation. The latter involves already the (static) particle-hole correlation function and we saw how e.g. the reduction of the moment of inertia by roughly a factor of two could be explained very easily in an analytic way. We very clearly pointed out the necessity to treat particles (holes) individually in Thomas Fermi approximation. A further very promising result is that the linear response function for transferred momenta q>0.6 fm-1 can be very accurately represented in our p-h-Thomas Fermi approach. In the last paragraph we give somewhat speculative arguments that say the 2+ states of quasi macroscopic Fermi Liquid Drops could be well calculated in expanding the time dependent density matrix on a set of coherent states and a simple example for nearly harmonic potentials is given
Institute of Scientific and Technical Information of China (English)
刘洪毓
2007-01-01
Atoms(原子)are all around us.They are something like the bricks (砖块)of which everything is made. The size of an atom is very,very small.In just one grain of salt are held millions of atoms. Atoms are very important.The way one object acts depends on what
Anomalous Weyl superfluid in three-dimensional ultracold fermionic gases
Huang, Beibing
2016-08-01
In this paper we use layer construction method to construct an experimentally feasible model to realize one type of anomalous Weyl superfluids (WS) in the context of cold fermionic gases. This exotic phase still characterizes the Weyl points in the bulk but completely different Majorana Fermi arc surface state (MFASS) on the boundaries. In contrast to conventional WS, where MFASS only connects the projection of Weyl points, new MFASS continuously stretches to the border of surface Brillouin zone. We self-consistently determine the phase diagram of model at the mean-field level to claim the achievement of anomalous WS. In addition, inversion symmetry and band inversion in this model are analyzed in detail to provide unique feature of identifying anomalous WS experimentally by momentum-resolved radio-frequency spectroscopy.
Phase correlations and quasicondensate in a two-dimensional ultracold Fermi gas
International Nuclear Information System (INIS)
The interplay between dimensionality, coherence and interaction in superfluid Fermi gases is analyzed by the phase correlation function of the field of fermionic pairs. We calculate this phase correlation function for a two-dimensional superfluid Fermi gas with s-wave interactions within the Gaussian pair fluctuation formalism. The spatial behavior of the correlation function is shown to exhibit a rapid (exponential) decay at short distances and a characteristic algebraic decay at large distances, with an exponent matching that expected from the Berezinskii–Kosterlitz–Thouless theory of 2D Bose superfluids. We conclude that the Gaussian pair fluctuation approximation is able to capture the physics of quasi-long-range order in two-dimensional Fermi gases. - Highlights: • The phase correlation functions for an ultracold Fermi gas in 2D are calculated. • The decay of the correlation functions is algebraic at long distances. • The Gaussian pair fluctuation approach is shown to capture the quasicondensate physics in 2D Fermi gases
International Nuclear Information System (INIS)
Completed by recent contributions on various topics (atoms and the Brownian motion, the career of Jean Perrin, the evolution of atomic physics since Jean Perrin, relationship between scientific atomism and philosophical atomism), this book is a reprint of a book published at the beginning of the twentieth century in which the author addressed the relationship between atomic theory and chemistry (molecules, atoms, the Avogadro hypothesis, molecule structures, solutes, upper limits of molecular quantities), molecular agitation (molecule velocity, molecule rotation or vibration, molecular free range), the Brownian motion and emulsions (history and general features, statistical equilibrium of emulsions), the laws of the Brownian motion (Einstein's theory, experimental control), fluctuations (the theory of Smoluchowski), light and quanta (black body, extension of quantum theory), the electricity atom, the atom genesis and destruction (transmutations, atom counting)
Dark matter superfluidity and galactic dynamics
Directory of Open Access Journals (Sweden)
Lasha Berezhiani
2016-02-01
Full Text Available We propose a unified framework that reconciles the stunning success of MOND on galactic scales with the triumph of the ΛCDM model on cosmological scales. This is achieved through the physics of superfluidity. Dark matter consists of self-interacting axion-like particles that thermalize and condense to form a superfluid in galaxies, with ∼mK critical temperature. The superfluid phonons mediate a MOND acceleration on baryonic matter. Our framework naturally distinguishes between galaxies (where MOND is successful and galaxy clusters (where MOND is not: dark matter has a higher temperature in clusters, and hence is in a mixture of superfluid and normal phase. The rich and well-studied physics of superfluidity leads to a number of striking observational signatures.
Dark matter superfluidity and galactic dynamics
Berezhiani, Lasha; Khoury, Justin
2016-02-01
We propose a unified framework that reconciles the stunning success of MOND on galactic scales with the triumph of the ΛCDM model on cosmological scales. This is achieved through the physics of superfluidity. Dark matter consists of self-interacting axion-like particles that thermalize and condense to form a superfluid in galaxies, with ∼mK critical temperature. The superfluid phonons mediate a MOND acceleration on baryonic matter. Our framework naturally distinguishes between galaxies (where MOND is successful) and galaxy clusters (where MOND is not): dark matter has a higher temperature in clusters, and hence is in a mixture of superfluid and normal phase. The rich and well-studied physics of superfluidity leads to a number of striking observational signatures.
Dark Matter Superfluidity and Galactic Dynamics
Berezhiani, Lasha
2015-01-01
We propose a unified framework that reconciles the stunning success of MOND on galactic scales with the triumph of the LambdaCDM model on cosmological scales. This is achieved through the physics of superfluidity. Dark matter consists of self-interacting axion-like particles that thermalize and condense to form a superfluid in galaxies, with ~mK critical temperature. The superfluid phonons mediate a MOND acceleration on baryonic matter. Our framework naturally distinguishes between galaxies (where MOND is successful) and galaxy clusters (where MOND is not): dark matter has a higher temperature in clusters, and hence is in a mixture of superfluid and normal phase. The rich and well-studied physics of superfluidity leads to a number of striking observational signatures.
Mixtures of bosonic and fermionic atoms in optical lattices
International Nuclear Information System (INIS)
We discuss the theory of mixtures of bosonic and fermionic atoms in periodic potentials at zero temperature. We derive a general Bose-Fermi Hubbard Hamiltonian in a one-dimensional optical lattice with a superimposed harmonic trapping potential. We study the conditions for linear stability of the mixture and derive a mean-field criterion for the onset of a bosonic superfluid transition. We investigate the ground-state properties of the mixture in the Gutzwiller formulation of mean-field theory, and present numerical studies of finite systems. The bosonic and fermionic density distributions and the onset of quantum phase transitions to demixing and to a bosonic Mott-insulator are studied as a function of the lattice potential strength. The existence is predicted of a disordered phase for mixtures loaded in very deep lattices. Such a disordered phase possessing many degenerate or quasidegenerate ground states is related to a breaking of the mirror symmetry in the lattice
The scissors mode and superfluidity of a Bose-Einstein condensed gas
International Nuclear Information System (INIS)
This thesis deals with the fundamental relation between Bose-Einstein condensation and superfluidity. In particular an extensive study of the scissors mode of excitation in a Bose-Einstein condensed gas of 87Rb atoms is presented. The complex apparatus constructed for the condensate production and the pathway that leads to the quantum degeneracy through laser cooling, magnetic trapping and evaporative cooling of the atomic sample are described. Temperatures as low as 300 nK are achieved. At these temperatures about 2x104 atoms condense in the ground state of the magnetic trap, realizing the phenomenon predicted by A. Einstein in 1925. The scissors mode is excited in our experiment by a sudden rotation of the trap through a small angle. Its observation shows that a condensate is irrotational and as such a superfluid. Above the transition temperature the scissors oscillation occurs at two frequencies. The high-lying frequency corresponds to an irrotational velocity flow that is the classical counterpart of the superfluid oscillation. The low-lying one is instead related to rotational flow. Its absence and the occurrence of the single frequency oscillation for the condensate are the key features that indicate superfluidity. A systematic experimental study of the temperature dependent damping and frequency shifts of the mode is presented and compared with available theoretical predictions, finding a good agreement. This enabled the investigation of the relative motion of the superfluid through the normal fluid. The frequency shift of the mode as a function of temperature is consistent with a quenching of the moment of inertia as the temperature is reduced because of superfluidity. The fundamental relation between the scissors mode and the moment of inertia is also pointed out for partially condensed clouds in the context of linear response theory. In a semiclassical approximation the moment of inertia is directly derived from our scissors mode data. (author)
Two dimensional superfluidity and melting
International Nuclear Information System (INIS)
The author reviews the equilibrium theory of superfluidity and XY magnetism, due in large part to the seminal work of Kosterlitz and Thouless. A dynamic generalization of this theory, with application to third sound in helium films is discussed. The statistical mechanics of two-dimensional melting on both smooth and periodic substrates, is discussed. The dynamic version of the theory is sketched. A theory of melting dynamics is particularly important in interpreting of the experiments on melting and crystallization described earlier. Finally the theory as it applies to anisotropic media including layered materials like smectics, cholesterics, and Rayleigh-Benard convection cells, is discussed. (Auth.)
Superfluid properties of BPS monopoles
Lantsman, L
2006-01-01
This paper is devoted to demonstrating manifest superfluid properties of the Minkowskian Higgs model with vacuum BPS monopole solutions at assuming the "continuous" $\\sim S^2$ vacuum geometry in that model. It will be also argued that point hedgehog topological defects are present in the Minkowskian Higgs model with BPS monopoles. It turns out, and we show this, that the enumerated phenomena are compatible with the Faddeev-Popov "heuristic" quantization of the Minkowskian Higgs model with vacuum BPS monopoles, coming to fixing the Weyl (temporal) gauge $A_0=0$ for gauge fields $A$ in the Faddeev-Popov path integral.
Energy Technology Data Exchange (ETDEWEB)
Perraud, S
2007-12-15
This study aims at characterizing helium two phase flows, and to identify the dependence of their characteristics on various thermo-hydraulic parameters: vapour velocity, liquid height, vapour density, specificities of superfluidity. Both the engineer and the physicist's points of view are taken into consideration: the first one in terms of optimization of a particular cooling scheme based on a two-phase flow, and these second one in terms of more fundamental atomization-related questions. It has been shown that for velocities around 3 to 4 m/s, the liquid phase that was initially stratified undergoes an atomization through the presence of a drop haze carried by the vapor phase.This happens for superfluid helium as well as for normal helium without main differences on atomization.
Superfluid helium testing of a stainless steel to titanium piping transition joint
Energy Technology Data Exchange (ETDEWEB)
Soyars, W.; /Fermilab; Basti, A.; Bedeschi, F.; /INFN, Pisa; Budagov, J.; /Dubna, JINR; Foley, M.; Harms, E.; Klebaner, A.; Nagaitsev, S.; /Fermilab; Sabirov, B.; Dubna, JINR
2009-11-01
Stainless steel-to-titanium bimetallic transitions have been fabricated with an explosively bonded joint. This novel joining technique was conducted by the Russian Federal Nuclear Center, working under contract for the Joint Institute for Nuclear Research. These bimetallic transitions are being considered for use in future superconducting radio-frequency cavity cryomodule assemblies. This application requires cryogenic testing to demonstrate that this transition joint remains leak-tight when sealing superfluid helium. To simulate a titanium cavity vessel connection to a stainless steel service pipe, bimetallic transition joints were paired together to fabricate piping assemblies. These piping assemblies were then tested in superfluid helium conditions at Fermi National Accelerator Laboratory test facilities. The transition joint test program will be described. Fabrication experience and test results will be presented.
Sourie, Aurélien; Novak, Jérôme
2016-01-01
We present a numerical model for uniformly rotating superfluid neutron stars, for the first time with realistic microphysics including entrainment, in a fully general relativistic framework. We compute stationary and axisymmetric configurations of neutron stars composed of two fluids, namely superfluid neutrons and charged particles (protons and electrons), rotating with different rates around a common axis. Both fluids are coupled by entrainment, a non-dissipative interaction which in case of a non-vanishing relative velocity between the fluids, causes the fluid momenta being not aligned with the respective fluid velocities. We extend the formalism by Comer and Joynt (2003) in order to calculate the equation of state (EoS) and entrainment parameters for an arbitrary relative velocity. The resulting entrainment matrix fulfills all necessary sum rules and in the limit of small relative velocity our results agree with Fermi liquid theory ones, derived to lowest order in the velocity. This formalism is applied t...
Superfluid helium testing of a stainless steel to titanium piping transition joint
Soyars, W; Bedeschi, F; Budagov, J; Foley, M; Harms, E; Klebaner, A; Nagaitsev, S; Sabirov, B; 10.1063/1.3422408
2012-01-01
Stainless steel-to-titanium bimetallic transitions have been fabricated with an explosively bonded joint. This novel joining technique was conducted by the Russian Federal Nuclear Center, working under contract for the Joint Institute for Nuclear Research. These bimetallic transitions are being considered for use in future superconducting radio-frequency cavity cryomodule assemblies. This application requires cryogenic testing to demonstrate that this transition joint remains leak-tight when sealing superfluid helium. To simulate a titanium cavity vessel connection to a stainless steel service pipe, bimetallic transition joints were paired together to fabricate piping assemblies. These piping assemblies were then tested in superfluid helium conditions at Fermi National Accelerator Laboratory test facilities. The transition joint test program will be described. Fabrication experience and test results will be presented.
Xiong, Hongwei
2015-08-01
We consider the gravitational effect of quantum wave packets when quantum mechanics, gravity, and thermodynamics are simultaneously considered. Under the assumption of a thermodynamic origin of gravity, we propose a general equation to describe the gravitational effect of quantum wave packets. In the classical limit, this equation agrees with Newton's law of gravitation. For quantum wave packets, however, it predicts a repulsive gravitational effect. We propose an experimental scheme using superfluid helium to test this repulsive gravitational effect. Our studies show that, with present technology such as superconducting gravimetry and cold atom interferometry, tests of the repulsive gravitational effect for superfluid helium are within experimental reach.
Dicke superradiance as nondestructive probe for the state of atoms in optical lattices
Brinke, Nicolai ten; Schützhold, Ralf
2016-05-01
We present a proposal for a probing scheme utilizing Dicke superradiance to obtain information about ultracold atoms in optical lattices. A probe photon is absorbed collectively by an ensemble of lattice atoms generating a Dicke state. The lattice dynamics (e.g., tunneling) affects the coherence properties of that Dicke state and thus alters the superradiant emission characteristics - which in turn provides insight into the lattice (dynamics). Comparing the Bose-Hubbard and the Fermi-Hubbard model, we find similar superradiance in the strongly interacting Mott insulator regime, but crucial differences in the weakly interacting (superfluid or metallic) phase. Furthermore, we study the possibility to detect whether a quantum phase transition between the two regimes can be considered adiabatic or a quantum quench.
Direct spectroscopic observation of elementary excitations in superfluid He droplets
International Nuclear Information System (INIS)
The absorption spectra of the electronic S1 left-arrow S0 transition of glyoxal molecules (C2H2O2) embedded in He droplets (≅5500 atoms) show well-resolved vibronic bands with a width -1. The phonon wings at higher frequencies have distinct gaps amounting to ΔE=8.1 K followed by a small maximum at 14.8K.The phonon wing shape agrees with a theoretical simulation based on the dispersion curve of elementary excitations in bulk He II, providing the first evidence for superfluidity in the finite-sized He droplets. copyright 1996 The American Physical Society
Color superfluidity and trion formation in ultracold fermionic systems
International Nuclear Information System (INIS)
We investigate the low temperature properties of the three component Hubbard model. This system might be realized by trapping 3 different hyperfine states of ultracold Li-6 atoms in optical lattices. Studies concerning the SU(3) symmetric attractive case based on a Gutzwiller variational method in d=∞ suggest that there is a continuous phase transition happening between a weak coupling color superfluid and a strong coupling trionic ground state. We construct and investigate the properties of the quantum field theory describing this quantum phase transition.
Directory of Open Access Journals (Sweden)
Efstathios E. Theotokoglou
2015-01-01
Full Text Available Two kinds of second-order nonlinear, ordinary differential equations (ODEs appearing in mathematical physics are analyzed in this paper. The first one concerns the Thomas-Fermi (TF equation, while the second concerns the Langmuir-Blodgett (LB equation in current flow. According to a mathematical methodology recently developed, the exact analytic solutions of both TF and LB ODEs are proposed. Both of these are nonlinear of the second order and by a series of admissible functional transformations are reduced to Abel’s equations of the second kind of the normal form. The closed form solutions of the TF and LB equations in the phase and physical plane are given. Finally a new interesting result has been obtained related to the derivative of the TF function at the limit.
Breathers on Quantized Superfluid Vortices
Salman, Hayder
2013-10-01
We consider the propagation of breathers along a quantized superfluid vortex. Using the correspondence between the local induction approximation (LIA) and the nonlinear Schrödinger equation, we identify a set of initial conditions corresponding to breather solutions of vortex motion governed by the LIA. These initial conditions, which give rise to a long-wavelength modulational instability, result in the emergence of large amplitude perturbations that are localized in both space and time. The emergent structures on the vortex filament are analogous to loop solitons but arise from the dual action of bending and twisting of the vortex. Although the breather solutions we study are exact solutions of the LIA equations, we demonstrate through full numerical simulations that their key emergent attributes carry over to vortex dynamics governed by the Biot-Savart law and to quantized vortices described by the Gross-Pitaevskii equation. The breather excitations can lead to self-reconnections, a mechanism that can play an important role within the crossover range of scales in superfluid turbulence. Moreover, the observation of breather solutions on vortices in a field model suggests that these solutions are expected to arise in a wide range of other physical contexts from classical vortices to cosmological strings.
Breathers on quantized superfluid vortices.
Salman, Hayder
2013-10-18
We consider the propagation of breathers along a quantized superfluid vortex. Using the correspondence between the local induction approximation (LIA) and the nonlinear Schrödinger equation, we identify a set of initial conditions corresponding to breather solutions of vortex motion governed by the LIA. These initial conditions, which give rise to a long-wavelength modulational instability, result in the emergence of large amplitude perturbations that are localized in both space and time. The emergent structures on the vortex filament are analogous to loop solitons but arise from the dual action of bending and twisting of the vortex. Although the breather solutions we study are exact solutions of the LIA equations, we demonstrate through full numerical simulations that their key emergent attributes carry over to vortex dynamics governed by the Biot-Savart law and to quantized vortices described by the Gross-Pitaevskii equation. The breather excitations can lead to self-reconnections, a mechanism that can play an important role within the crossover range of scales in superfluid turbulence. Moreover, the observation of breather solutions on vortices in a field model suggests that these solutions are expected to arise in a wide range of other physical contexts from classical vortices to cosmological strings. PMID:24182275
Superfluid Helium 3: Link Between Condensed Matter Physics and Particle Physics
International Nuclear Information System (INIS)
The discovery of the superfluid phases of Helium 3 in 1971 opened the door to one of the most fascinating systems known in condensed matter physics. Superfluidity of Helium 3, originating from pair condensation of Helium 3 atoms, turned out to be the ideal test ground for many fundamental concepts of modern physics, such as macroscopic quantum phenomena, (gauge-)symmetries and their spontaneous breakdown, topological defects, etc. Thereby the superfluid phases of Helium 3 enriched condensed matter physics enormously. In particular, they contributed significantly - and continue to do so - to our understanding of various other physical systems, from heavy fermion and high-Tc superconductors all the way to neutron stars, particle physics, gravity and the early universe. A simple introduction into the basic concepts and questions is presented. (author)
Variational wavefunction for multi-species spinful fermionic superfluids and superconductors
International Nuclear Information System (INIS)
We introduce a new fermionic variational wavefunction, generalizing the Bardeen–Cooper–Schrieffer (BCS) wavefunction, which is suitable for interacting multi-species spinful systems and sustaining superfluidity. Applications range from quark matter to the high temperature superconductors. A wide class of Hamiltonians, comprising interactions and hybridization of arbitrary momentum dependence between different fermion species, can be treated in a comprehensive manner. This is the case, as both the intra-species and the inter-species interactions are treated on equally rigorous footing, which is accomplished via the introduction of a new quantum index attached to the fermions. The index is consistent with known fermionic physics, and allows for heretofore unaccounted fermion–fermion correlations. We have derived the finite temperature version of the theory, thus obtaining the renormalized quasiparticle dispersion relations, and we discuss the appearance of charge and spin density wave order. We present numerical solutions for two electron species in 2 dimensions. Based on these solutions, we show that, for equivalent spin up and down fermions, the Fermi occupation factor (per spin) equals 1/2 deep in the Fermi sea. This constitutes a unique experimental prediction of the theory, both for the normal and superfluid states. Interestingly, this result, obtained in the thermodynamic limit, is consistent with Fermi occupation factor (in-)equalities for finite systems of electrons, derived (in a different context) by Borland and Dennis (1972) and by Altunbulak and Klyachko (2008)
Holographic superconductors and superfluids - effect of backreaction
International Nuclear Information System (INIS)
Recently, the gravity-gauge theory correspondence has been used to describe so-called holographic superconductors and superfluids with the help of black holes in Anti-de Sitter space-time. In this talk, I discuss holographic superconductors and superfluids away from the probe limit, i.e. taking backreaction of the space-time into account. In the first part of the talk I present our results for Gauss-Bonnet holographic superconductors in (3+1) dimensions, while the second part deals with holographic superfluids in (2+1) dimensions where one of the spatial dimensions is compactified.
Superfluid Optomechanics: Coupling of a Superfluid to a Superconducting Condensate
DeLorenzo, L A
2013-01-01
We investigate the low loss acoustic motion of superfluid $^4$He parametrically coupled to a very low loss, superconducting Nb, TE$_{011}$ microwave resonator, forming a gram-scale, sideband resolved, optomechanical system. We demonstrate the detection of a series of acoustic modes with quality factors as high as $7\\cdot 10^6$. At higher temperatures, the lowest dissipation modes are limited by an intrinsic three phonon process. Acoustic quality factors approaching $10^{11}$ may be possible in isotopically purified samples at temperatures below 10 mK. A system of this type may be utilized to study macroscopic quantized motion and as an ultra-sensitive sensor of extremely weak displacements and forces, such as continuous gravity wave sources.
Superfluid optomechanics: coupling of a superfluid to a superconducting condensate
International Nuclear Information System (INIS)
We investigate the low loss acoustic motion of superfluid 4He parametrically coupled to a very low loss, superconducting Nb TE011 microwave resonator, forming a gram-scale, sideband resolved, optomechanical system. We demonstrate the detection of a series of acoustic modes with quality factors as high as 1.4×107. At higher temperatures, the lowest dissipation modes are limited by an intrinsic three phonon process. Acoustic quality factors approaching 1011 may be possible in isotopically purified samples at temperatures below 10 mK. A system of this type may be utilized to study macroscopic quantized motion and as a freqency tunable, ultra-sensitive sensor of extremely weak displacements and forces, such as continuous gravity wave sources. (paper)
Superfluid (quantum) turbulence and distributed chaos
Bershadskii, A
2016-01-01
Properties of distributed chaos in superfluid (quantum) turbulence have been studied using the data of recent direct numerical simulations (HVBK two-fluid model for He II, and a moving grid in the frames of Gross-Pitaevskii model of the Bose-Einstein condensates at low temperatures). It is found that for the viscous (normal) component of the velocity field in He II the viscosity dominates the distributed chaos with the stretched exponential spectrum $\\exp(-k/k_{\\beta})^{\\beta}$ and $\\beta = 2/3$. For the superfluid component the distributed chaos is dominated by the vorticity correlation integral with $\\beta =1/2$ (the soft spontaneous breaking of the space translational symmetry - homogeneity). For very low temperature the distributed chaos is tuned to the large-scale coherent motions: the viscous (normal) component is tuned to the fundamental mode, whereas the superfluid component is subharmonically tuned. For the Gross-Pitaevskii superfluid turbulence incompressible part of the energy spectrum (containing ...
Transition probabilities in superfluid He4
International Nuclear Information System (INIS)
The transition probabilities between various states of superfluid helium-4 are found by using the approximation method of Bogolyubov and making use of his canonical transformations for different states of transitions. (author)
Broken superfluid in dense quark matter
International Nuclear Information System (INIS)
Quark matter at high densities is a superfluid. Properties of the superfluid become highly non-trivial if the effects of strange-quark mass and the weak interactions are considered. These properties are relevant for a microscopic description of compact stars. We discuss the effect of a (small) explicitly symmetry-breaking term on the properties of a zero-temperature superfluid in a relativistic φ4 theory. If the U(1) symmetry is exact, chemical potential and superflow can be equivalently introduced either via (1) a background gauge field or (2) a topologically nontrivial mode. However, in the case of the explicitly broken symmetry, we demonstrate that the scenarios (1) and (2) lead to quantitatively different results for the mass of the pseudo-Goldstone mode and the critical velocity for superfluidity.
Spin-down Rate of Pinned Superfluid
Jahan-Miri, M
2006-01-01
The spinning down (up) of a superfluid is associated with a radial motion of its quantized vortices. In the presence of pinning barriers against the motion of the vortices, a spin-down may be still realized through ``random unpinning'' and ``vortex motion,'' as two physically separate processes, as suggested recently. The spin-down rate of a pinned superfluid is calculated, in this framework, by directly solving the equation of motion applicable to only the unpinned moving vortices, at any given time. The results indicate that the pinned superfluid in the crust of a neutron star may as well spin down at the same steady-state rate as the rest of the star, through random unpinning events, while pinning conditions prevail and the superfluid rotational lag is smaller than the critical lag value.
Didactic demonstrations of superfluidity and superconductivity phenomena
International Nuclear Information System (INIS)
In order to demonstrate to students phenomena of superfluidity and superconductivity a special helium cryostat has been constructed. The demonstrated effects, construction of the cryostat and the method of demonstration are described. (author)
A Theory of Dark Matter Superfluidity
Berezhiani, Lasha
2015-01-01
We propose a novel theory of dark matter (DM) superfluidity that matches the successes of the LambdaCDM model on cosmological scales while simultaneously reproducing the MOdified Newtonian Dynamics (MOND) phenomenology on galactic scales. The DM and MOND components have a common origin, representing different phases of a single underlying substance. DM consists of axion-like particles with mass of order eV and strong self-interactions. The condensate has a polytropic equation of state P~rho^3 giving rise to a superfluid core within galaxies. Instead of behaving as individual collisionless particles, the DM superfluid is more aptly described as collective excitations. Superfluid phonons, in particular, are assumed to be governed by a MOND-like effective action and mediate a MONDian acceleration between baryonic matter particles. Our framework naturally distinguishes between galaxies (where MOND is successful) and galaxy clusters (where MOND is not): due to the higher velocity dispersion in clusters, and corres...
梯状光晶格中自旋轨道耦合的排斥费米气体%Spin-orbit coupled Fermi atoms loaded in an optical ladder lattice
Institute of Scientific and Technical Information of China (English)
郭飞翔; 周晓凡; 赵华
2015-01-01
采用密度矩阵重整化群 ( density-matrix-renormalization-group, DMRG) 方法, 研究梯状光晶格中排斥相互作用费米气体的基态属性. 研究表明, Zeeman场能够激发系统的相分离 (完全极化相和部分极化相), 而自旋轨道耦合效应能抑制相分离, 使整个晶格处于部分极化相, 在不同的强弱排斥相互作用系统中, 极化率会随自旋轨道耦合改变表现出不同的变化规律.%The density-matrix-renormalization-group ( DMRG ) method is used to numerically calculate the ground state of repulsively interacting Fermi atoms loaded in optical ladder lattices. It is found that the system exhibits the spatial separation of a fully spin-polarized phase from the partially polarized phase for the suitable intensity of Zeeman field without the effect of spin-orbit coupled atoms. The spin-orbit coupling drives the fully spin-polarized phase to the partially spin-polarized phase in the whole system. The spin polarizations of weak and strong repulsively interac-ting systems vary differently with spin-orbit interaction strength.
Fermi: a physicist in the upheaval
International Nuclear Information System (INIS)
This book summarizes the life, works and complex personality of the Italian physicist Enrico Fermi (1901-1954) whose myth is linked with the political upheaval of the 2. world war: the youth of an autodidact, the theorician and the quantum mechanics, his invention of a quantum statistics, the weak interaction theory, his works on artificial radioactivity, the end of the Fermi team and his exile in the USA, the secrete researches at the university of Columbia and the birth of the first atomic 'pile' (December 2, 1942), the building of Los Alamos center and the Alamogordo explosion test, the disagreements among the physicists of the Manhattan project and the position of Fermi, Fermi's contribution in the H-bomb construction, the creation of the physics school of Chicago, the Oppenheimer spying affair. (J.S.)
Microphotonic Forces From Superfluid Flow
McAuslan, D L; Baker, C; Sachkou, Y; He, X; Sheridan, E; Bowen, W P
2015-01-01
In cavity optomechanics, radiation pressure and photothermal forces are widely utilized to cool and control micromechanical motion, with applications ranging from precision sensing and quantum information to fundamental science. Here, we realize an alternative approach to optical forcing based on superfluid flow and evaporation in response to optical heating. We demonstrate optical forcing of the motion of a cryogenic microtoroidal resonator at a level of 1.46 nN, roughly one order of magnitude larger than the radiation pressure force. We use this force to feedback cool the motion of a microtoroid mechanical mode to 137 mK. The photoconvective forces demonstrated here provide a new tool for high bandwidth control of mechanical motion in cryogenic conditions, and have the potential to allow efficient transfer of electromagnetic energy to motional kinetic energy.
Breathers on Quantized Superfluid Vortices
Salman, Hayder
2013-01-01
We consider the propagation of breathers along a quantised superfluid vortex. Using the correspondence between the local induction approximation (LIA) and the nonlinear Schr\\"odinger equation, we identify a set of initial conditions corresponding to breather solutions of vortex motion governed by the LIA. These initial conditions, which give rise to a long-wavelength modulational instability, result in the emergence of large amplitude perturbations that are localised in both space and time. The emergent structures on the vortex filament are analogous to loop solitons. Although the breather solutions we study are exact solutions of the LIA equations, we demonstrate through full numerical simulations that their key emergent attributes carry over to vortex dynamics governed by the Biot-Savart law and to quantized vortices described by the Gross-Pitaevskii equation. The breather excitations can lead to self-reconnections, a mechanism that can play an important role within the cross-over range of scales in superfl...
Electric response in superfluid helium
Chagovets, Tymofiy V.
2016-05-01
We report an experimental investigation of the electric response of superfluid helium that arises in the presence of a second sound standing wave. It was found that the signal of the electric response is observed in a narrow range of second sound excitation power. The linear dependence of the signal amplitude has been derived at low excitation power, however, above some critical power, the amplitude of the signal is considerably decreased. It was established that the rapid change of the electric response is not associated with a turbulent regime generated by the second sound wave. A model of the appearance of the electric response as a result of the oscillation of electron bubbles in the normal fluid velocity field in the second sound wave is presented. Possible explanation for the decrease of the electric response are presented.
Two-dimensional superfluid transition in Hdown
International Nuclear Information System (INIS)
The surface density as function of temperature for Hdown adsorbed on superfluid helium film is studied for several gas densities. The theory used is exact in the low density limit and predict Kosterlitz-thouless transition temperatures lower than previous calculation and also lower saturation density. The results confirm the possibility of a 2D superfluid transition under conditions close to those achieved experimentally. (Author)
Spin-down Rate of Pinned Superfluid
Jahan-Miri, M.
2006-01-01
The spinning down (up) of a superfluid is associated with a radial motion of its quantized vortices. In the presence of pinning barriers against the motion of the vortices, a spin-down may be still realized through ``random unpinning'' and ``vortex motion,'' as two physically separate processes, as suggested recently. The spin-down rate of a pinned superfluid is calculated, in this framework, by directly solving the equation of motion applicable to only the unpinned moving vortices, at any gi...
Strongly-correlated ultracold atoms in optical lattices
International Nuclear Information System (INIS)
This thesis is concerned with the theoretical study of strongly correlated quantum states of ultra-cold fermionic atoms trapped in optical lattices. This field has grown considerably in recent years, following the experimental progress made in cooling and controlling atomic gases, which has led to the observation of the first Bose-Einstein condensation (in 1995). The trapping of these gases in optical lattices has opened a new field of research at the interface between atomic physics and condensed matter physics. The observation of the transition from a superfluid to a Mott insulator for bosonic atoms paved the way for the study of strongly correlated phases and quantum phase transitions in these systems. Very recently, the investigation of the Mott insulator state of fermionic atoms provides additional motivation to conduct such theoretical studies. This thesis can be divided broadly into two types of work: - On the one hand, we have proposed a new type of spectroscopy to measure single-particle correlators and associated physical observables in these strongly correlated states. - On the other hand, we have studied the ground state of the fermionic Hubbard model under different conditions (mass imbalance, population imbalance) by using analytical techniques and numerical simulations. In a collaboration with J. Dalibard and C. Salomon (LKB at the ENS Paris) and I. Carusotto (Trento, Italy), we have proposed and studied a novel spectroscopic method for the measurement and characterization of single particle excitations (in particular, the low energy excitations, namely the quasiparticles) in systems of cold fermionic atoms, with energy and momentum resolution. This type of spectroscopy is an analogue of angular-resolved photoemission in solid state physics (ARPES). We have shown, via simple models, that this method of measurement can characterize quasiparticles not only in the 'conventional' phases such as the weakly interacting gas in the lattice or in Fermi
Resonant superfluidity in an optical lattice
International Nuclear Information System (INIS)
We study a system of ultracold fermionic Potassium (40K) atoms in a three-dimensional optical lattice in the neighborhood of an s-wave Feshbach resonance. Close to resonance, the system is described by a multi-band Bose-Fermi Hubbard Hamiltonian. We derive an effective lowest-band Hamiltonian in which the effect of the higher band is incorporated by a self-consistent mean-field approximation. The resulting model is solved by means of Generalized Dynamical Mean-Field Theory. In addition to the BEC/BCS crossover we find on the BCS side of the resonance a phase transition to a fermionic Mott insulator at half filling, induced by the repulsive fermionic background scattering length. We also calculate the critical temperature of the BEC/BCS-state across the resonance and find it to be minimal at resonance.
Condensate and final-state effects in superfluid {sup 4}He
Energy Technology Data Exchange (ETDEWEB)
Azuah, R.T.; Stirling, W.G. [Department of Physics, University of Keele, Keele ST5 5BG (United Kingdom); Glyde, H.R.; Boninsegni, M. [Department of Physics and Astronomy, University of Delaware, Newark, Delaware 19716 (United States); Sokol, P.E. [Department of Physics, Pennsylvania State University, University Park, Pennsylvania 16802 (United States); Bennington, S.M. [ISIS Division, Rutherford Appleton Laboratory, Didcot OX11 0QX (United Kingdom)
1997-12-01
We present high-precision measurements of the dynamics of single atoms in superfluid {sup 4}He at T=1.6 K and saturated vapor pressure. The measurements were taken on the MARI instrument at the ISIS neutron-scattering facility, Rutherford-Appleton Laboratory. From the measurements we obtain a condensate fraction n{sub 0}=6.0{plus_minus}2.0{percent} at T=1.6 K. The final-state effects (FSE{close_quote}s) in the atomic response are also determined from the data in the form of a final-state broadening function, R(Q,y). We find that this FS function is the same in the superfluid at T=1.6 K as that determined previously in normal {sup 4}He at T=2.3 K. If we reanalyze the data assuming that the superfluid has no condensate, i.e., n{sub 0}=0, then the data requires that the normal n({bold k}) change dramatically between T=2.3 K and T=1.6 K. Since such a change in n({bold k}) is physically unexpected, given that kT is much less than the zero-point energy, the data requires that a new contribution, such as a condensate, enter n({bold k}) in the superfluid. {copyright} {ital 1997} {ital The American Physical Society}
Wu, Shuyuan; Xu, Jun; Lee, Chaohong
2016-01-01
According to the famous Kibble-Zurek mechanism (KZM), the universality of spontaneous defect generation in continuous phase transitions (CPTs) can be understood by the critical slowing down. In most CPTs of atomic Bose-Einstein condensates (BECs), the universality of spontaneous defect generations has been explained by the divergent relaxation time associated with the nontrivial gapless Bogoliubov excitations. However, for atomic BECs in synthetic gauge fields, their spontaneous superfluidity breakdown is resulted from the divergent correlation length associated with the zero Landau critical velocity. Here, by considering an atomic BEC ladder subjected to a synthetic magnetic field, we reveal that the spontaneous superfluidity breakdown obeys the KZM. The Kibble-Zurek scalings are derived from the Landau critical velocity which determines the correlation length. In further, the critical exponents are numerically extracted from the critical spatial-temporal dynamics of the bifurcation delay and the spontaneous...
Paoletti, Matthew
2010-11-01
Long-range quantum order underlies a number of related physical phenomena including superfluidity, superconductivity and Bose-Einstein condensation. While superfluidity in helium-4 was one of the earliest discovered, it is not the best understood, owing to the strong interactions present (making theoretical progress difficult) and the lack of local experimental probes. Quantum fluids, such as superfluid helium-4, are typically described as a mixture of two interpenetrating fluids with distinct velocity fields: a viscous normal fluid akin to water and an inviscid superfluid exhibiting long-range quantum order. In this "two-fluid model," there is no conventional viscous dissipation in the superfluid component and vorticity is confined to atomically-thin vortices with quantized circulation. Turbulence may occur in either fluid component with turbulence in the superfluid exhibiting a complex tangle of quantized vortices, as first envisioned by Feynman. Approximately five years ago, our group discovered that micron-sized hydrogen particles may be used for flow visualization in superfluid helium-4. The particles can trace the motions of the normal fluid or be trapped by the quantized vortices, which enables one to characterize the dynamics of both the normal fluid and superfluid components for the first time. By directly observing and tracking these particles, we have directly confirmed the two-fluid model, observed vortex rings and quantized vortex reconnection, characterized thermal counterflows, and observed the very peculiar nature of quantum turbulence. One of many surprising observations is the existence of power-law tails in the probability distribution of velocities in quantum turbulence, which are in stark contrast to the Gaussian distributions typical of classical fluid turbulence.
Molecular regimes in ultracold Fermi gases
D.S. Petrov; C. Salomon; G.V. Shlyapnikov
2009-01-01
The use of Feshbach resonances for tuning the interparticle interaction in ultracold Fermi gases has led to remarkable developments, in particular to the creation and Bose-Einstein condensation of weakly bound diatomic molecules of fermionic atoms. These are the largest diatomic molecules obtained s
Enrico Fermi and the Old Quantum Physics
De Gregorio, Alberto; Sebastiani, Fabio
2009-01-01
We outline Fermi's early attitude towards old quantum physics. We sketch out the context from which his interest for quantum physics arose, and we deal with his work on quantum statistics. We also go through the first two courses on theoretical physics he held in Rome, and his 1928 book on atomic physics.
Fermi Liquid Instabilities in the Spin Channel
Energy Technology Data Exchange (ETDEWEB)
Wu, Congjun; /Santa Barbara, KITP; Sun, Kai; Fradkin, Eduardo; /Illinois U., Urbana; Zhang, Shou-Cheng; /Stanford U., Phys. Dept.
2010-03-16
We study the Fermi surface instabilities of the Pomeranchuk type in the spin triplet channel with high orbital partial waves (F{sub l}{sup a} (l > 0)). The ordered phases are classified into two classes, dubbed the {alpha} and {beta}-phases by analogy to the superfluid {sup 3}He-A and B-phases. The Fermi surfaces in the {alpha}-phases exhibit spontaneous anisotropic distortions, while those in the {beta}-phases remain circular or spherical with topologically non-trivial spin configurations in momentum space. In the {alpha}-phase, the Goldstone modes in the density channel exhibit anisotropic overdamping. The Goldstone modes in the spin channel have nearly isotropic underdamped dispersion relation at small propagating wavevectors. Due to the coupling to the Goldstone modes, the spin wave spectrum develops resonance peaks in both the {alpha} and {beta}-phases, which can be detected in inelastic neutron scattering experiments. In the p-wave channel {beta}-phase, a chiral ground state inhomogeneity is spontaneously generated due to a Lifshitz-like instability in the originally nonchiral systems. Possible experiments to detect these phases are discussed.
Coexistence of superfluid and metallic-like state in two-component fermionic systems
Energy Technology Data Exchange (ETDEWEB)
Continentino, M.A., E-mail: mucio@cbpf.br [Centro Brasileiro de Pesquisas Físicas, Rua Dr. Xavier Sigaud 150, 22290-180 Rio de Janeiro, RJ (Brazil); Padilha, Igor T. [Universidade Federal do Amazonas, Departamento de Física, Av. Gal. Rodrigo Octávio Jordão Ramos, 3000 Setor Sul e Norte, Coroado I, Manaus (Brazil)
2012-01-09
We study the possibility of coexistence in a two component fermionic system of a superfluid state with a metallic-like state with gapless excitations at a Fermi surface. We consider a two-component system with mixing (hybridization) between them and attractive interactions between only one type of quasi-particles. Besides a conventional BCS regime, we find for sufficiently strong interactions a superfluid state of Bose condensed pairs at zero temperature. We investigate whether these pairs can coexist with a metallic-like state characterized by gapless electronic excitations. The zero temperature phase diagram as a function of the strength of the attractive interaction and the mixing is obtained. For simplicity and to clarify the nature of the quantum phase diagram we consider the case of s-wave pairing. -- Highlights: ► We study superconductivity in a multi-component system along the BCS–BEC crossover. ► The T=0 phase diagram exhibits different regimes for the superfluid phases. ► We find a new metallic phase with fermions coexisting with preformed pairs. ► Superconductivity is destroyed from the BEC-like regime.
Sourie, Aurélien; Oertel, Micaela; Novak, Jérôme
2016-04-01
We present a numerical model for uniformly rotating superfluid neutron stars in a fully general relativistic framework with, for the first time, realistic microphysics including entrainment. We compute stationary and axisymmetric configurations of neutron stars composed of two fluids, namely superfluid neutrons and charged particles (protons and electrons), rotating with different rates around a common axis. Both fluids are coupled by entrainment, a nondissipative interaction which in the case of a nonvanishing relative velocity between the fluids causes the fluid momenta to be not aligned with the respective fluid velocities. We extend the formalism put forth by Comer and Joynt in order to calculate the equation of state (EOS) and entrainment parameters for an arbitrary relative velocity as far as superfluidity is maintained. The resulting entrainment matrix fulfills all necessary sum rules, and in the limit of small relative velocity our results agree with Fermi liquid theory ones derived to lowest order in the velocity. This formalism is applied to two new nuclear equations of state which are implemented in the numerical model, which enables us to obtain precise equilibrium configurations. The resulting density profiles and moments of inertia are discussed employing both EOSs, showing the impact of entrainment and the dependence on the EOS.
Topological States in a One-Dimensional Fermi Gas with Attractive Interactions
Ruhman, Jonathan; Berg, Erez; Altman, Ehud
2014-01-01
We describe a novel topological superfluid state, which forms in a one-dimensional Fermi gas with Rashba-like spin-orbit coupling, a Zeeman field and intrinsic attractive interactions. In spite of total number conservation and the presence of gapless excitations, Majorana-like zero modes appear in this system and can be linked with interfaces between two distinct phases that naturally form at different regions of the harmonic trap. As a result, the low lying collective excitations of the syst...
Neutron Fermi Liquids under the presence of a strong magnetic field with effective nuclear forces
Perez-Garcia, M Angeles; Polls, A
2009-01-01
Landau's Fermi Liquid parameters are calculated for non-superfluid pure neutron matter in the presence of a strong magnetic field at zero temperature. The particle-hole interactions in the system, where a net magnetization may be present, are characterized by these parameters in the framework of a multipolar formalism. We use either zero- or finite-range effective nuclear forces to describe the nuclear interaction. Using the obtained Fermi Liquid parameters, the effect of a strong magnetic field on some bulk magnitudes such as isothermal compressibility and spin susceptibility is also investigated.
Generalized Seniority Description of Cold Fermi Gases
G. E. Brown; Gelman, B. A.; Kuo, T. T. S.
2004-01-01
We suggest that the extension of the Racah seniority description of strongly interacting fermions in the nuclear shell model is directly generalizable to describe pairing of atoms in cold Fermi systems. We illustrate this by the fermionic pairing in the much studied cold two-component gas of Li atoms. Our pairing interaction is two orders of magnitude stronger than that used in the usual BCS approach. We also explain why the Racah scheme is less applicable to nuclei, and discuss the similarit...
Dark Energy and Dark Matter in a Superfluid Universe
Huang, Kerson
2013-01-01
The vacuum is filled with complex scalar fields, such as the Higgs field. These fields serve as order parameters for superfluidity (quantum phase coherence over macroscopic distances), making the entire universe a superfluid. We review a mathematical model consisting of two aspects: (a) emergence of the superfluid during the big bang; (b) observable manifestations of superfluidity in the present universe. The creation aspect requires a self-interacting scalar field that is asymptotically free...
Vortex Phases of Rotating Superfluids
International Nuclear Information System (INIS)
We report on the first mathematically rigorous proofs of a transition to a giant vortex state of a superfluid in rotating anharmonic traps. The analysis is carried out within two-dimensional Gross-Pitaevskii theory at large coupling constant and large rotational velocity and is based on precise asymptotic estimates on the ground state energy. An interesting aspect is a significant difference between 'soft' anharmonic traps (like a quartic plus quadratic trapping potential) and traps with a fixed boundary. In the former case vortices persist in the bulk until the width of the annulus becomes comparable to the size of the vortex cores. In the second case the transition already takes place in a parameter regime where the size of vortices is very small relative to the width of the annulus. Moreover, the density profiles in the annulus are different in the two cases. In both cases rotational symmetry of the density in a true ground state is broken, even though a symmetric variational ansatz gives an excellent approximation to the energy.
Holographic Superfluidity in Imbalanced Mixtures
Erdmenger, Johanna; Kerner, Patrick; Ngo, Thanh Hai
2011-01-01
We construct superfluid black hole solutions with two chemical potentials. By analogy with QCD, the two chemical potentials correspond to the baryon and isospin symmetries, respectively. We consider two systems: the back-reacted U(2) Einstein-Yang-Mills theory in 4+1 dimensions and the 9+1-dimensional D3/D7 brane setup with two coincident D7-brane probes. In the D7-brane model, the identification of baryon and isospin chemical potential is explicit since the dual field theory is explicitly known. Studying the phase diagram, we find in both systems a quantum phase transition at a critical ratio of the two chemical potentials. However the quantum phase transition is different in the two systems: In the D3/D7 brane setup we always find a second order phase transition, while in the Einstein-Yang-Mills theory, depending on the strength of the back-reaction, we obtain a continuous or first order transition. We expect the continuous quantum phase transition to be BKT-like. We comment on the origin of this differing ...
Size effects in superfluid 3He
International Nuclear Information System (INIS)
The superfluid density and transition temperature of 3He filling the pores of packed alumina powder have been measured by fourth sound. The measurements were performed simultaneously for three separate fourth sound resonators, each packed with a different nominal grain size of 1.0 μm. 0.3 μm and 0.05 μm. The bulk 3He superfluid transition temperature, which was determined independently, was compared to the transition temperature of each resonator. We observed a systematic depression for both the superfluid density and transition temperature as the powder size was decreased. The depressions in the transition temperature were compared with theoretical estimates of size dependent transition temperatures for the ideal geometry of an infinite cylinder. In the analysis the cylinder radius was replaced by defining an average radius of the pore structure which was empirically determined by nitrogen gas sorption and mercury intrusion techniques. The pressure dependence of the transition temperature depression is found to be consistent with theoretical estimates of the superfluid coherence length. The experimentally determined magnitude of the coherence length based on the pore structure analysis is in agreement with theoretical estimates, confirming that the coherence length of superfluid 3He is about two orders of magnitude larger than that of He II
Orbital angular momentum injection in a polariton superfluid.
Boulier, T.; Glorieux, Q.; Cancellieri, E.; Giacobino, E.; Bramati, A.
2015-01-01
We report a new method for injecting angular momentum in a polariton superfluid. Rather than stirring, such as what is done in atomic BECs, we resonantly inject a ring-shaped rotating superfluid in a planar semiconductor cavity. The resonant injection avoids any significant exciton populations and ensures a high level of control in the system. A Spatial Light Modulator is used to create a Laguerre-Gaussian laser beam that pumps the system and creates a rotating polariton population. By using a l = 8 Laguerre-Gaussian mode we have studied the steady-state condition for observing the nucleation of angular momentum in freely propagating polaritons at the center. We find that, likely due to the fixed border conditions, the angular momentum in weak cavity disorder areas does not spontaneously nucleates at the center, and we observe a single l = 8 vortex. For larger cavity disorder vortex-antivortex pairs can nucleate and we present numerical simulations that explain the role of this disorder to observe such a nucleation.
Extension of Radiative Viscosity to Superfluid Matter
Institute of Scientific and Technical Information of China (English)
PI Chun-Mei; YANG Shu-Hua; ZHENG Xiao-Ping
2011-01-01
The radiative viscosity of superfluid npe matter is studied and it is found that to the lowest order of δμ/T,the ratio of radiative viscosity to bulk viscosity is the same as that of its normal matter.As one of the most important transport coefficients,the bulk viscosities of simple npe matter,of hyperon matter and even of quark matter,both in normal and superfluid states,have been extensively studied,[1-18] for more detail see Ref.[19].%The radiative viscosity of superfluid npe matter is studied and it is found that to the lowest order of δμ/T, the ratio of radiative viscosity to bulk viscosity is the same as that of its normal matter.
An introduction to experiments on superfluid turbulence
International Nuclear Information System (INIS)
A description of the experimental background of superfluid turbulence was assigned to me for this lecture. Superfluid turbulence, or as some call it, quantum turbulence, has been an active field of physics since the 1950's. The field was pioneered experimentally and theoretically by Joe Vinen and as such is approaching a half century in age. It is safe to say that with few exceptions the results are unknown to those investigators who are interested in classical turbulence, that is the kind of investigation which has been pioneered by Taylor, Landau, Kolmogorov and others. It has only recently been realized that liquid helium I, liquid helium II and cryogenic (critical) helium gas are attractive candidates for investigating classical turbulence problems, and in the process many have decided to look at the kinds of challenges encountered in using helium II, that phase of liquid helium which exhibits superfluidity. (orig.)
Transport coefficients in superfluid neutron stars
Energy Technology Data Exchange (ETDEWEB)
Tolos, Laura [Instituto de Ciencias del Espacio (IEEC/CSIC) Campus Universitat Autònoma de Barcelona, Facultat de Ciències, Torre C5, E-08193 Bellaterra (Barcelona) (Spain); Frankfurt Institute for Advances Studies. Johann Wolfgang Goethe University, Ruth-Moufang-Str. 1, 60438 Frankfurt am Main (Germany); Manuel, Cristina [Instituto de Ciencias del Espacio (IEEC/CSIC) Campus Universitat Autònoma de Barcelona, Facultat de Ciències, Torre C5, E-08193 Bellaterra (Barcelona) (Spain); Sarkar, Sreemoyee [Tata Institute of Fundamental Research, Homi Bhaba Road, Mumbai-400005 (India); Tarrus, Jaume [Physik Department, Technische Universität München, D-85748 Garching (Germany)
2016-01-22
We study the shear and bulk viscosity coefficients as well as the thermal conductivity as arising from the collisions among phonons in superfluid neutron stars. We use effective field theory techniques to extract the allowed phonon collisional processes, written as a function of the equation of state and the gap of the system. The shear viscosity due to phonon scattering is compared to calculations of that coming from electron collisions. We also comment on the possible consequences for r-mode damping in superfluid neutron stars. Moreover, we find that phonon collisions give the leading contribution to the bulk viscosities in the core of the neutron stars. We finally obtain a temperature-independent thermal conductivity from phonon collisions and compare it with the electron-muon thermal conductivity in superfluid neutron stars.
Superfluid helium-4 in one dimensional channel
Kim, Duk Y.; Banavar, Samhita; Chan, Moses H. W.; Hayes, John; Sazio, Pier
2013-03-01
Superfluidity, as superconductivity, cannot exist in a strict one-dimensional system. However, the experiments employing porous media showed that superfluid helium can flow through the pores of nanometer size. Here we report a study of the flow of liquid helium through a single hollow glass fiber of 4 cm in length with an open id of 150 nm between 1.6 and 2.3 K. We found the superfluid transition temperature was suppressed in the hollow cylinder and that there is no flow above the transition. Critical velocity at temperature below the transition temperature was determined. Our results bear some similarity to that found by Savard et. al. studying the flow of helium through a nanohole in a silicon nitrite membrane. Experimental study at Penn State is supported by NSF Grants No. DMR 1103159.
Note on Zero Temperature Holographic Superfluids
Guo, Minyong; Niu, Chao; Tian, Yu; Zhang, Hongbao
2016-01-01
In this note, we have addressed various issues on zero temperature holographic superfluids. First, inspired by our numerical evidence for the equality between the superfluid density and particle density, we provide an elegant analytic proof for this equality by a boost trick. Second, using not only the frequency domain analysis but also the time domain analysis from numerical relativity, we identify the hydrodynamic normal modes and calculate out the sound speed, which is shown to increase with the chemical potential and saturate to the value predicted by the conformal field theory in the large chemical potential limit. Third, the generic non-thermalization is demonstrated by the fully non-linear time evolution from a non-equilibrium state for our zero temperature holographic superfluid. Furthermore, a conserved Noether charge is proposed in support of this behavior.
Note on zero temperature holographic superfluids
Guo, Minyong; Lan, Shanquan; Niu, Chao; Tian, Yu; Zhang, Hongbao
2016-06-01
In this note, we have addressed various issues on zero temperature holographic superfluids. First, inspired by our numerical evidence for the equality between the superfluid density and particle density, we provide an elegant analytic proof for this equality by a boost trick. Second, using not only the frequency domain analysis but also the time domain analysis from numerical relativity, we identify the hydrodynamic normal modes and calculate out the sound speed, which is shown to increase with the chemical potential and saturate to the value predicted by the conformal field theory in the large chemical potential limit. Third, the generic non-thermalization is demonstrated by the fully nonlinear time evolution from a non-equilibrium state for our zero temperature holographic superfluid. Furthermore, a conserved Noether charge is proposed in support of this behavior.
Turbulent velocity spectra in superfluid flows
Salort, J; Castaing, B; Chabaud, B; Daviaud, F; Didelot, T; Diribarne, P; Dubrulle, B; Gagne, Y; Gauthier, F; Girard, A; Hébral, B; Rousset, B; Thibault, P; Roche, P -E; 10.1063/1.3504375
2012-01-01
We present velocity spectra measured in three cryogenic liquid 4He steady flows: grid and wake flows in a pressurized wind tunnel capable of achieving mean velocities up to 5 m/s at temperatures above and below the superfluid transition, down to 1.7 K, and a "chunk" turbulence flow at 1.55 K, capable of sustaining mean superfluid velocities up to 1.3 m/s. Depending on the flows, the stagnation pressure probes used for anemometry are resolving from one to two decades of the inertial regime of the turbulent cascade. We do not find any evidence that the second order statistics of turbulence below the superfluid transition differ from the ones of classical turbulence, above the transition.
Fermi liquid theory: A brief survey in memory of Gerald E. Brown
International Nuclear Information System (INIS)
I present a brief review of Fermi liquid theory, and discuss recent work on Fermi liquid theory in dilute neutron matter and cold atomic gases. I argue that recent interest in transport properties of quantum fluids provides fresh support for Landau's approach to Fermi liquid theory, which is based on kinetic theory rather than effective field theory and the renormalization group. I also discuss work on non-Fermi liquids, in particular dense quark matter
Fermi liquid theory: A brief survey in memory of Gerald E. Brown
Schaefer, Thomas
2014-01-01
I present a brief review of Fermi liquid theory, and discuss recent work on Fermi liquid theory in dilute neutron matter and cold atomic gases. I argue that renewed interest in transport properties of quantum fluids provides fresh support for Landau's approach to Fermi liquid theory, which is based on kinetic theory rather than effective field theory and the renormalization group. I also discuss work on non-Fermi liquids, in particular dense quark matter.
Exotic properties of superfluid helium 3
Volovik, GE
1992-01-01
This book discusses the unique properties of superfluid phases of 3He, the condensed matter with the outmost broken symmetry, which combine in a surprising way the properties of ordered magnets, liquid crystals and superfluids. The complicated vacuum state of these phases with a large number of fermionic and bosonic quasiparticles and topological objects remains the vacuum in modern quantum field theories. Some of the objects and physical phenomena in 3He have strong analogy with the neutrino, W-bosons, weak interactions, gravity, chiral anomaly, Quantum Hall Effect and fractional statistics.
Teaching superfluidity at the introductory level
Schmets, Alexander J. M.; Montfrooij, Wouter
2008-01-01
Standard introductory modern physics textbooks do not exactly dwell on superfluidity in 4He. Typically, Bose-Einstein condensation (BEC) is mentioned in the context of an ideal Bose gas, followed by the statement that BEC happens in 4He and that the ground state of 4He exhibits many interesting properties such as having zero viscosity. Not only does this approach not explain in any way why 4He becomes a superfluid, it denies students the opportunity to learn about the far reaching consequence...
How superfluid vortex knots untie
Kleckner, Dustin; Kauffman, Louis H.; Irvine, William T. M.
2016-07-01
Knots and links often occur in physical systems, including shaken strands of rope and DNA (ref. ), as well as the more subtle structure of vortices in fluids and magnetic fields in plasmas. Theories of fluid flows without dissipation predict these tangled structures persist, constraining the evolution of the flow much like a knot tied in a shoelace. This constraint gives rise to a conserved quantity known as helicity, offering both fundamental insights and enticing possibilities for controlling complex flows. However, even small amounts of dissipation allow knots to untie by means of `cut-and-splice’ operations known as reconnections. Despite the potentially fundamental role of these reconnections in understanding helicity--and the stability of knotted fields more generally--their effect is known only for a handful of simple knots. Here we study the evolution of 322 elemental knots and links in the Gross-Pitaevskii model for a superfluid, and find that they universally untie. We observe that the centreline helicity is partially preserved even as the knots untie, a remnant of the perfect helicity conservation predicted for idealized fluids. Moreover, we find that the topological pathways of untying knots have simple descriptions in terms of minimal two-dimensional knot diagrams, and tend to concentrate in states which are twisted in only one direction. These results have direct analogies to previous studies of simple knots in several systems, including DNA recombination and classical fluids. This similarity in the geometric and topological evolution suggests there are universal aspects in the behaviour of knots in dissipative fields.
Superfluid properties of a Bose-Einstein condensate in an optical lattice confined in a cavity
Bhattacherjee, A. B.
2007-01-01
We study the effect of a one dimensional optical lattice in a cavity field with quantum properties on the superfluid dynamics of a Bose-Einstein condensate(BEC). In the cavity the influence of atomic backaction and the external driving pump become important and strongly modify the optical potential. Due to the strong coupling between the condensate wavefunction and the cavity modes, the cavity light field develops a band structure. This study reveals that the pump and the cavity emerges as a ...
NASA
2009-01-01
1. This view from NASA's Fermi Gamma-ray Space Telescope is the deepest and best-resolved portrait of the gamma-ray sky to date. The image shows how the sky appears at energies more than 150 million times greater than that of visible light. Among the signatures of bright pulsars and active galaxies is something familiar -- a faint path traced by the sun. (Credit: NASA/DOE/Fermi LAT Collaboration) 2. The Large Area Telescope (LAT) on Fermi detects gamma-rays through matter (electrons) and antimatter (positrons) they produce after striking layers of tungsten. (Credit: NASA/Goddard Space Flight Center Conceptual Image Lab)
Impact of medium effects on the cooling of non-superfluid and superfluid neutron stars
Schaab, C; Sedrakian, A D; Weber, F; Weigel, M K
1996-01-01
Neutrino emission from the dense hadronic component in neutron stars is subject to strong modifications due to collective effects in the nuclear medium. We implement two new neutrino--emission processes operating in the nuclear medium in numerical cooling simulations of neutron stars. The first process is the medium--modified Urca (MMU) process, which takes into account the softening of the pion exchange mode and other polarization effects as well as the neutrino emission arising from the intermediate reaction states in the modified Urca process. The second process concerns neutrino emission through superfluid pair formation and breaking processes. It is found that non--superfluid neutron star models cool mainly via the MMU process, which gives a smooth crossover from the standard to the nonstandard cooling scenario for increasing star masses. For superfluid stars, the superfluid pair formation and breaking processes accelerate mildly both the standard and the nonstandard cooling scenario. This leads to a goo...
National Aeronautics and Space Administration — Fermi is a powerful space observatory that will open a wide window on the universe. Gamma rays are the highest-energy form of light, and the gamma-ray sky is...
National Aeronautics and Space Administration — All analysis results presented here are preliminary and are not intended as an official catalog of Fermi-LAT detected GRBs. Please consult the table's caveat page...
Energy Technology Data Exchange (ETDEWEB)
Kontrym-Sznajd, G. [Polska Akademia Nauk, Wroclaw (Poland). Inst. Niskich Temperatur i Badan Strukturalnych; Sormann, H. [Technische Univ., Graz (Austria). Inst. fuer Theoretische Physik; West, R.N. [Texas Univ., Arlington, TX (United States). Dept. of Physics
2001-07-01
Electron-positron momentum densities in Y, reconstructed from two-dimensional angular correlation of annihilation radiation spectra, are compared with the theoretical predictions of fully-relativistic augmented plane-wave calculations. Knowledge of the theoretical densities and of the effects on them of certain symmetry selection rules has allowed us to separate two hole Fermi surfaces in the third and fourth bands and to establish some Fermi momenta for each of them. (orig.)
Energy Technology Data Exchange (ETDEWEB)
Das, Priyam; Panigrahi, Prasanta K [Indian Institute of Science Education and Research (IISER), Salt Lake, Kolkata-700 106 (India); Vyas, Manan, E-mail: daspriyam3@gmail.co [Physical Research Laboratory, Navrangpura, Ahmedabad-380 009 (India)
2009-12-28
In a one-dimensional shallow optical lattice, in the presence of both cubic and quintic nonlinearity, a superfluid density wave is identified in a Bose-Einstein condensate. Interestingly, it ceases to exist when only one of these interactions is operative. We predict the loss of superfluidity through a classical dynamical phase transition, where modulational instability leads to the loss of phase coherence. In a certain parameter domain, the competition between lattice potential and the interactions is shown to give rise to a stripe phase, where atoms are confined in finite domains. In a pure two-body case, apart from the known superfluid and insulating phases, a density wave insulating phase is found to exist, possessing two frequency modulations commensurate with the lattice potential.
Energy Density Functional Approach to Superfluid Nuclei
Yu, Yongle; Bulgac, Aurel
2002-01-01
We show that within the framework of a simple local nuclear energy density functional (EDF), one can describe accurately the one-- and two--nucleon separation energies of semi--magic nuclei. While for the normal part of the EDF we use previously suggested parameterizations, for the superfluid part of the EDF we use the simplest possible local form compatible with known nuclear symmetries.
Enrico Fermi centenary exhibition seminar
Maximilien Brice
2002-01-01
Photo 01: Dr. Juan Antonio Rubio, Leader of the Education and Technology Transfer Division and CERN Director General, Prof. Luciano Maiani. Photo 03: Luciano Maiani, Welcome and Introduction Photo 09: Antonino Zichichi, The New 'Centro Enrico Fermi' at Via Panisperna Photos 10, 13: Ugo Amaldi, Fermi at Via Panisperna and the birth of Nuclear Medicine Photo 14: Jack Steinberger, Fermi in Chicago Photo 18: Valentin Telegdi, A close-up of Fermi Photo 21: Arnaldo Stefanini, Celebrating Fermi's Centenary in Documents and Pictures.
Atomic spectra in a helium bubble
Nakatsukasa, Takashi; Yabana, Kazuhiro; Bertsch, George F.
2002-01-01
Density functional theory (DFT) is applied to atomic spectra under perturbations of superfluid liquid helium. The atomic DFT of helium is used to obtain the distribution of helium atoms around the impurity atom, and the electronic DFT is applied to the excitations of the atom, averaging over the ensemble of helium configurations. The shift and broadening of the D1 and D2 absorption lines are quite well reproduced by theory, suggesting that the DFT may be useful for describing spectral perturb...
International Nuclear Information System (INIS)
We present a general method for obtaining the exact static solutions and collective excitation frequencies of a trapped Bose-Einstein condensate (BEC) with dipolar atomic interactions in the Thomas-Fermi regime. The method incorporates analytic expressions for the dipolar potential of an arbitrary polynomial density profile, thereby reducing the problem of handling nonlocal dipolar interactions to the solution of algebraic equations. We comprehensively map out the static solutions and excitation modes, including non-cylindrically-symmetric traps, and also the case of negative scattering length where dipolar interactions stabilize an otherwise unstable condensate. The dynamical stability of the excitation modes gives insight into the onset of collapse of a dipolar BEC. We find that global collapse is consistently mediated by an anisotropic quadrupolar collective mode, although there are two trapping regimes in which the BEC is stable against quadrupole fluctuations even as the ratio of the dipolar to s-wave interactions becomes infinite. Motivated by the possibility of a fragmented condensate in a dipolar Bose gas due to the partially attractive interactions, we pay special attention to the scissors modes, which can provide a signature of superfluidity, and identify a long-range restoring force which is peculiar to dipolar systems. As part of the supporting material for this paper we provide the computer program used to make the calculations, including a graphical user interface.
Enrico Fermi exhibition at CERN
2002-01-01
A touring exhibition celebrating the centenary of Enrico Fermi's birth in 1901 will be on display at CERN (Main Building, Mezzanine) from 12-27 September. You are cordially invited to the opening celebration on Thursday 12 September at 16:00 (Main Building, Council Chamber), which will include speechs from: Luciano Maiani Welcome and Introduction Arnaldo Stefanini Celebrating Fermi's Centenary in Documents and Pictures Antonino Zichichi The New 'Centro Enrico Fermi' at Via Panisperna Ugo Amaldi Fermi at Via Panisperna and the birth of Nuclear Medicine Jack Steinberger Fermi in Chicago Valentin Telegdi A Close-up of Fermi and the screening of a documentary video about Fermi: Scienziati a Pisa: Enrico Fermi (Scientists at Pisa: Enrico Fermi) created by Francesco Andreotti for La Limonaia from early film, photographs and sound recordings (In Italian, with English subtitles - c. 30 mins). This will be followed by an aperitif on the Mezz...
Superfluid and antiferromagnetic phases in ultracold fermionic quantum gases
International Nuclear Information System (INIS)
In this thesis several models are treated, which are relevant for ultracold fermionic quantum gases loaded onto optical lattices. In particular, imbalanced superfluid Fermi mixtures, which are considered as the best way to realize Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) states experimentally, and antiferromagnetic states, whose experimental realization is one of the next major goals, are examined analytically and numerically with the use of appropriate versions of the Hubbard model. The usual Bardeen-Cooper-Schrieffer (BCS) superconductor is known to break down in a magnetic field with a strength exceeding the size of the superfluid gap. A spatially inhomogeneous spin-imbalanced superconductor with a complex order parameter known as FFLO-state is predicted to occur in translationally invariant systems. Since in ultracold quantum gases the experimental setups have a limited size and a trapping potential, we analyze the realistic situation of a non-translationally invariant finite sized Hubbard model for this purpose. We first argue analytically, why the order parameter should be real in a system with continuous coordinates, and map our statements onto the Hubbard model with discrete coordinates defined on a lattice. The relevant Hubbard model is then treated numerically within mean field theory. We show that the numerical results agree with our analytically derived statements and we simulate various experimentally relevant systems in this thesis. Analogous calculations are presented for the situation at repulsive interaction strength where the N'eel state is expected to be realized experimentally in the near future. We map our analytical results obtained for the attractive model onto corresponding results for the repulsive model. We obtain a spatially invariant unit vector defining the direction of the order parameter as a consequence of the trapping potential, which is affirmed by our mean field numerical results for the repulsive case. Furthermore, we observe
Facile time-of-flight methods for characterizing pulsed superfluid helium droplet beams
Energy Technology Data Exchange (ETDEWEB)
He, Yunteng; Zhang, Jie; Li, Yang; Freund, William M.; Kong, Wei, E-mail: wei.kong@oregonstate.edu [Department of Chemistry, Oregon State University, Corvallis, Oregon 97331 (United States)
2015-08-15
We present two facile time-of-flight (TOF) methods of detecting superfluid helium droplets and droplets with neutral dopants. Without an electron gun and with only a heated filament and pulsed electrodes, the electron impact ionization TOF mass spectrometer can resolve ionized helium clusters such as He{sub 2}{sup +} and He{sub 4}{sup +}, which are signatures of superfluid helium droplets. Without ionizing any helium atoms, multiphoton non-resonant laser ionization of CCl{sub 4} doped in superfluid helium droplets at 266 nm generates complex cluster ions of dopant fragments with helium atoms, including (He){sub n}C{sup +}, (He){sub n}Cl{sup +}, and (He){sub n}CCl{sup +}. Using both methods, we have characterized our cryogenic pulsed valve—the Even-Lavie valve. We have observed a primary pulse with larger helium droplets traveling at a slower speed and a rebound pulse with smaller droplets at a faster speed. In addition, the pickup efficiency of dopant is higher for the primary pulse when the nozzle temperature is higher than 13 K, and the total time duration of the doped droplet pulse is only on the order of 20 μs. These results stress the importance of fast and easy characterization of the droplet beam for sensitive measurements such as electron diffraction of doped droplets.
Facile time-of-flight methods for characterizing pulsed superfluid helium droplet beams.
He, Yunteng; Zhang, Jie; Li, Yang; Freund, William M; Kong, Wei
2015-08-01
We present two facile time-of-flight (TOF) methods of detecting superfluid helium droplets and droplets with neutral dopants. Without an electron gun and with only a heated filament and pulsed electrodes, the electron impact ionization TOF mass spectrometer can resolve ionized helium clusters such as He2(+) and He4(+), which are signatures of superfluid helium droplets. Without ionizing any helium atoms, multiphoton non-resonant laser ionization of CCl4 doped in superfluid helium droplets at 266 nm generates complex cluster ions of dopant fragments with helium atoms, including (He)(n)C(+), (He)(n)Cl(+), and (He)(n)CCl(+). Using both methods, we have characterized our cryogenic pulsed valve—the Even-Lavie valve. We have observed a primary pulse with larger helium droplets traveling at a slower speed and a rebound pulse with smaller droplets at a faster speed. In addition, the pickup efficiency of dopant is higher for the primary pulse when the nozzle temperature is higher than 13 K, and the total time duration of the doped droplet pulse is only on the order of 20 μs. These results stress the importance of fast and easy characterization of the droplet beam for sensitive measurements such as electron diffraction of doped droplets. PMID:26329210
Facile time-of-flight methods for characterizing pulsed superfluid helium droplet beams
International Nuclear Information System (INIS)
We present two facile time-of-flight (TOF) methods of detecting superfluid helium droplets and droplets with neutral dopants. Without an electron gun and with only a heated filament and pulsed electrodes, the electron impact ionization TOF mass spectrometer can resolve ionized helium clusters such as He2+ and He4+, which are signatures of superfluid helium droplets. Without ionizing any helium atoms, multiphoton non-resonant laser ionization of CCl4 doped in superfluid helium droplets at 266 nm generates complex cluster ions of dopant fragments with helium atoms, including (He)nC+, (He)nCl+, and (He)nCCl+. Using both methods, we have characterized our cryogenic pulsed valve—the Even-Lavie valve. We have observed a primary pulse with larger helium droplets traveling at a slower speed and a rebound pulse with smaller droplets at a faster speed. In addition, the pickup efficiency of dopant is higher for the primary pulse when the nozzle temperature is higher than 13 K, and the total time duration of the doped droplet pulse is only on the order of 20 μs. These results stress the importance of fast and easy characterization of the droplet beam for sensitive measurements such as electron diffraction of doped droplets
Vortex-Core Structure in Neutral Fermion Superfluids with Population Imbalance
International Nuclear Information System (INIS)
Quantized vortex-core structure is theoretically investigated in fermion superfluids with population imbalance for two atom species of neutral atom clouds near a Feshbach resonance. In contrast with the vortex core in balance case where the quantum depletion makes a vortex visible through the density profile measurement, the vortex core is filled in and becomes less visible because the quantized discrete bound states are occupied exclusively by the majority species. Yet it is shown that the core can be visible through the minority density profile experiment using phase contrast imaging, revealing an interesting opportunity to examine low-lying fermionic core bound states unexplored so far
He, Yunteng; Zhang, Jie; Kong, Wei
2016-02-28
We compare characteristics of electron impact ionization (EI) and multiphoton ionization (MPI) of doped superfluid helium droplets using the same droplet source. Selected dopant ion fragments from the two ionization schemes demonstrate different dependence on the doping pressure, which could be attributed to the different ionization mechanisms. While EI directly ionizes helium atoms in a droplet therefore has higher yields for bigger droplets (within a limited size range), MPI is insensitive to the helium in a droplet and is only dependent on the number of dopant molecules. The optimal timing of the ionization pulse also varies with the doping pressure, implying a velocity slip among different sized droplets. Calculations of the doping statistics and ionization probabilities qualitatively agree with the experimental data. Our results offer a word of caution in interpreting the pressure and timing dependence of superfluid helium droplets, and we also devise a scheme in achieving a high degree of doping while limiting the contribution of dopant clusters. PMID:26931697
Chiral magnetism and spontaneous spin Hall effect of interacting Bose superfluids.
Li, Xiaopeng; Natu, Stefan S; Paramekanti, Arun; Das Sarma, S
2014-01-01
Recent experiments on ultracold atoms in optical lattices have synthesized a variety of tunable bands with degenerate double-well structures in momentum space. Such degeneracies in the single-particle spectrum strongly enhance quantum fluctuations, and often lead to exotic many-body ground states. Here we consider weakly interacting spinor Bose gases in such bands, and discover a universal quantum 'order by disorder' phenomenon which selects a novel superfluid with chiral spin order displaying remarkable properties such as spontaneous spin Hall effect and momentum space antiferromagnetism. For bosons in the excited Dirac band of a hexagonal lattice, such a state supports staggered spin loop currents in real space. We show that Bloch oscillations provide a powerful dynamical route to quantum state preparation of such a chiral spin superfluid. Our predictions can be readily tested in spin-resolved time-of-flight experiments. PMID:25300774
Absence of small-scale structure in homogeneous superfluid turbulence
International Nuclear Information System (INIS)
By contrast with classical turbulence, which is driven by large-scale shear instabilities, superfluid turbulence is driven homogeneously by the mutual friction between the normal fluid and the superfluid. We suggest that this difference implies that there is no equivalent to a Kolmogorov energy cascade in turbulent superfluid flows. We then compare a recent numerical simulation of superfluid turbulence by Schwartz [Phys. Rev. B 31, 5782 (1985)] with a recent simulation of singular vortex stretching in classical fluids by Siggia and Pumir. This comparison suggests that the rigidity of the quantum-mechanical vortex core inhibits any generation of small-scale structure in the superfluid case. Superfluid turbulence is essentially a two-length-scale phenomenon, where the scales are the average intervortex distance and the vortex-core diameter
Zero Temperature Holographic Superfluids with Two Competing Orders
Li, Ran; Zhang, Hongbao; Zhao, Junkun
2016-01-01
We initiate the investigation of the zero temperature holographic superfluids with two competing orders, where besides the vacuum phase, two one band superfluid phases, the coexistent superfluid phase has also been found in the AdS soliton background for the first time. We construct the complete phase diagram in the $e-\\mu$ plane by numerics, which is consistent with our qualitative analysis. Furthermore, we calculate the corresponding optical conductivity and sound speed by the linear response theory. The onset of pole of optical conductivity at $\\omega=0$ indicates that the spontaneous breaking phase always represents the superfluid phase, and the residue of pole is increased with the chemical potential, which is consistent with the fact that the particle density is essentially the superfluid density for zero temperature superfluids. In addition, the resulting sound speed demonstrates the non-smoothness at the critical points as the order parameter of condensate, which indicates that the phase transitions c...
2009-01-01
In only 10 months of scientific activity, the Fermi space observatory has already collected an unprecedented wealth of information on some of the most amazing objects in the sky. In a recent talk at CERN, Luca Latronico, a member of the Fermi collaboration, explained some of their findings and emphasized the strong links between High Energy Physics (HEP) and High Energy Astrophysics (HEA). The Fermi gamma-ray telescope was launched by NASA in June 2008. After about two months of commissioning it started sending significant data back to the Earth. Since then, it has made observations that are changing our view of the sky: from discovering a whole new set of pulsars, the greatest total energy gamma-ray burst ever, to detecting an unexplained abundance of high-energy electrons that could be a signature of dark matter, to producing a uniquely rich and high definition sky map in gamma-rays. The high performance of the instrument comes as ...
D'Agostini, G
2005-01-01
It is curious to learn that Enrico Fermi knew how to base probabilistic inference on Bayes theorem, and that some influential notes on statistics for physicists stem from what the author calls elsewhere, but never in these notes, {\\it the Bayes Theorem of Fermi}. The fact is curious because the large majority of living physicists, educated in the second half of last century -- a kind of middle age in the statistical reasoning -- never heard of Bayes theorem during their studies, though they have been constantly using an intuitive reasoning quite Bayesian in spirit. This paper is based on recollections and notes by Jay Orear and on Gauss' ``Theoria motus corporum coelestium'', being the {\\it Princeps mathematicorum} remembered by Orear as source of Fermi's Bayesian reasoning.
Fractal generalization of Thomas-Fermi model
Rekhviashvili, S. Sh.; Sokurov, A. A.
2016-05-01
The Thomas-Fermi model is developed for a multielectron neutral atom at an arbitrary metric dimension of the electron cloud. It has been shown that the electron cloud with the reduced dimension should be located in the close vicinity of the nucleus. At a metric dimension of the electron cloud of 2, the differential equation of the model admits an analytical solution. In this case, the screening parameter does not depend on the charge of the nucleus.
Instability of Superfluid Flow in the Neutron Star Inner Crust
Link, Bennett
2011-01-01
I examine the hydrodynamic stability of a pinned superfluid vortex lattice undergoing thermal creep under the Magnus force in the inner crust of a spinning down neutron star. The superfluid flow is unstable over length scales $\\lap 10$ m, possibly over timescales of days to minutes. The vortex lattice could degenerate into a tangle, and the superfluid flow could become turbulent. Unexpectedly large dissipation would suppress the instability.
Energy Technology Data Exchange (ETDEWEB)
Yocum, D.R.; Berman, E.; Canal, P.; Chadwick, K.; Hesselroth, T.; Garzoglio, G.; Levshina, T.; Sergeev, V.; Sfiligoi, I.; Sharma, N.; Timm, S.; /Fermilab
2007-05-01
As one of the founding members of the Open Science Grid Consortium (OSG), Fermilab enables coherent access to its production resources through the Grid infrastructure system called FermiGrid. This system successfully provides for centrally managed grid services, opportunistic resource access, development of OSG Interfaces for Fermilab, and an interface to the Fermilab dCache system. FermiGrid supports virtual organizations (VOs) including high energy physics experiments (USCMS, MINOS, D0, CDF, ILC), astrophysics experiments (SDSS, Auger, DES), biology experiments (GADU, Nanohub) and educational activities.
Electron bubbles and Weyl fermions in chiral superfluid 3He-A
Shevtsov, Oleksii; Sauls, J. A.
2016-08-01
Electrons embedded in liquid 3He form mesoscopic bubbles with large radii compared to the interatomic distance between 3He atoms, voids of Nbubble≈200 3He atoms, generating a negative ion with a large effective mass that scatters thermal excitations. Electron bubbles in chiral superfluid 3He-A also provide a local probe of the ground state. We develop a scattering theory of Bogoliubov quasiparticles by negative ions embedded in 3He-A that incorporates the broken symmetries of 3He-A , particularly broken symmetries under time reversal and mirror symmetry in a plane containing the chiral axis l ̂. Multiple scattering by the ion potential, combined with branch conversion scattering by the chiral order parameter, leads to a spectrum of Weyl fermions bound to the ion that support a mass current circulating the electron bubble—a mesoscopic realization of chiral edge currents in superfluid 3He-A films. A consequence is that electron bubbles embedded in 3He-A acquire angular momentum, L ≈-(Nbubble/2 ) ℏ l ̂ , inherited from the chiral ground state. We extend the scattering theory to calculate the forces on a moving electron bubble, both the Stokes drag and a transverse force, FW=e/c v ×BW , defined by an effective magnetic field, BW∝l ̂ , generated by the scattering of thermal quasiparticles off the spectrum of Weyl fermions bound to the moving ion. The transverse force is responsible for the anomalous Hall effect for electron bubbles driven by an electric field reported by the RIKEN group. Our results for the scattering cross section, drag, and transverse forces on moving ions are compared with experiments and shown to provide a quantitative understanding of the temperature dependence of the mobility and anomalous Hall angle for electron bubbles in normal and superfluid 3He-A . We also discuss our results in relation to earlier work on the theory of negative ions in superfluid 3He.
A new look at Thomas–Fermi theory
DEFF Research Database (Denmark)
Solovej, Jan Philip
2015-01-01
In this short note, we argue that Thomas–Fermi theory, the simplest of all density functional theories, although failing to explain features such as molecular binding or stability of negative ions, is surprisingly accurate in estimating sizes of atoms. We give both numerical, experimental and...... rigorous mathematical evidence for this claim. Motivated by this, we formulate two new mathematical conjectures on the exactness of Thomas–Fermi theory....
A new look at Thomas-Fermi Theory
Solovej, Jan Philip
2016-01-01
In this short note we argue that Thomas-Fermi Theory the simplest of all density functional theories, although failing to explain features such as binding or stability of negative ions, is surprisingly accurate in estimating sizes of atoms. We give both numerical, experimental and rigorous mathematical evidence for this claim. Motivated by this we formulate two new mathematical conjectures on the exactness of Thomas-Fermi Theory.
Phase transitions in Bose-Fermi-Hubbard model in the heavy fermion limit: Hard-core boson approach
Directory of Open Access Journals (Sweden)
I.V. Stasyuk
2015-12-01
Full Text Available Phase transitions are investigated in the Bose-Fermi-Hubbard model in the mean field and hard-core boson approximations for the case of infinitely small fermion transfer and repulsive on-site boson-fermion interaction. The behavior of the Bose-Einstein condensate order parameter and grand canonical potential is analyzed as functions of the chemical potential of bosons at zero temperature. The possibility of change of order of the phase transition to the superfluid phase in the regime of fixed values of the chemical potentials of Bose- and Fermi-particles is established. The relevant phase diagrams are built.
Modern trends in superconductivity and superfluidity
Kagan, M Yu
2013-01-01
This book concisely presents the latest trends in the physics of superconductivity and superfluidity and magnetism in novel systems, as well as the problem of BCS-BEC crossover in ultracold quantum gases and high-Tc superconductors. It further illuminates the intensive exchange of ideas between these closely related fields of condensed matter physics over the last 30 years of their dynamic development. The content is based on the author’s original findings obtained at the Kapitza Institute, as well as advanced lecture courses he held at the Moscow Engineering Physical Institute, Amsterdam University, Loughborough University and LPTMS Orsay between 1994 and 2011. In addition to the findings of his group, the author discusses the most recent concepts in these fields, obtained both in Russia and in the West. The book consists of 16 chapters which are divided into four parts. The first part describes recent developments in superfluid hydrodynamics of quantum fluids and solids, including the fashionable subject...
Dark matter superfluid and DBI dark energy
Cai, Rong-Gen; Wang, Shao-Jiang
2016-01-01
It was shown recently that, without jeopardizing the success of the Λ cold dark matter model on cosmic scales, the modified Newtonian dynamics (MOND) can be derived as an emergent phenomenon when axionlike dark matter particles condense into superfluid on the galactic scales. We propose in this paper a Dirac-Born-Infeld (DBI) scalar field conformally coupled to the matter components. To maintain the success of MOND phenomenon of dark matter superfluid on the galactic scales, the fifth force introduced by the DBI scalar should be screened on the galactic scales. It turns out that the screening effect naturally leads to a simple explanation for a longstanding puzzle that the MOND critical acceleration coincides with present Hubble scale. This galactic coincidence problem is solved, provided that the screened DBI scalar also plays the role of dark energy on the cosmic scales.
Bistability in a Driven-Dissipative Superfluid
Labouvie, Ralf; Santra, Bodhaditya; Heun, Simon; Ott, Herwig
2016-06-01
We experimentally study a driven-dissipative Josephson junction array, realized with a weakly interacting Bose-Einstein condensate residing in a one-dimensional optical lattice. Engineered losses on one site act as a local dissipative process, while tunneling from the neighboring sites constitutes the driving force. We characterize the emerging steady states of this atomtronic device. With increasing dissipation strength γ the system crosses from a superfluid state, characterized by a coherent Josephson current into the lossy site, to a resistive state, characterized by an incoherent hopping transport. For intermediate values of γ , the system exhibits bistability, where a superfluid and an incoherent branch coexist. We also study the relaxation dynamics towards the steady state, where we find a critical slowing down, indicating the presence of a nonequilibrium phase transition.
Position-dependent oscillated decay of a two-level atom immersed in a two-dimensional photon fluid
Zhang, Xiongfeng; Yin, Miao; Liang, Wenyao
2016-01-01
A Weisskopf-Wigner theory has been used to investigate the spontaneous emission of a two-level atom placed in a photon superfluid. It is found that the atom decays exponentially. However, the atomic decay rate changes periodically with the position of the atom and it is minimal when the atom is located at the wave nodes. The largest decay rate of the atom in photon superfluid has the same order of magnitude as it is in vacuum of free space. Moreover, the analytical result shows that the decay of an atom in photon superfluid, compared with that in planar cavity without photon superfluid, will be inhibited. The physical origin of atomic decay inhibition is also discussed.
Superfluid Helium Flow in Porous Media
Allain, Hervé; Quintard, Michel; Soulaine, Cyprien; Prat, Marc; Baudouy, Bertrand; Van Weelderen, Rob
2013-01-01
Superfluid helium is primarily used in the field of applied superconductivity. Given the complexity of the magnet geometry and the scales involved, a real 3D simulation of heat transfer in such devices at the micro-channel scale is very difficult, even impossible. However, the repeatability or even periodicity of the structure suggests the possibility of a macro-scale description following a porous medium approach. Which macro-scale model may be used? This largely remains an open field while ...
Quantum Gravity as Theory of "Superfluidity"
Barbashov, B. M.; Pervushin, V. N.; Zakharov, A. F.; Zinchuk, V. A.
2005-01-01
A version of the cosmological perturbation theory in general relativity (GR) is developed, where the cosmological scale factor is identified with spatial averaging of the metric determinant logarithm and the cosmic evolution acquires the pattern of a superfluid motion: the absence of "friction-type" interaction, the London-type wave function, and the Bogoliubov condensation of quantum universes. This identification keeps the number of variables of GR and leads to a new type of potential pertu...
Superfluid dynamics of 258Fm fission
Scamps, Guillaume; Simenel, Cédric; Lacroix, Denis
2015-01-01
Theoretical description of nuclear fission remains one of the major challenges of quantum many-body dynamics. The slow, mostly adiabatic motion through the fission barrier is followed by a fast, non-adiabatic descent of the potential between the fragments. The latter stage is essentially unexplored. However, it is crucial as it generates most of the excitation energy in the fragments. The superfluid dynamics in the latter stage of fission is obtained with the time-dependent Hartree-Fock theor...
Superfluidity of grain boundaries and supersolid behavior.
Sasaki, S; Ishiguro, R; Caupin, F; Maris, H J; Balibar, S
2006-08-25
When two communicating vessels are filled to a different height with liquid, the two levels equilibrate because the liquid can flow. We have looked for such equilibration with solid (4)He. For crystals with no grain boundaries, we see no flow of mass, whereas for crystals containing several grain boundaries, we detect a mass flow. Our results suggest that the transport of mass is due to the superfluidity of grain boundaries. PMID:16873608
Chiral superfluidity for the heavy ion collisions
Energy Technology Data Exchange (ETDEWEB)
Kalaydzhyan, T. [Deutsches Elektronen-Synchrotron (DESY), Hamburg (Germany); Institute of Theoretical and Experimental Physics, Moscow (Russian Federation)
2013-02-15
We argue that the strongly coupled quark-gluon plasma formed at LHC and RHIC can be considered as a chiral superfluid. The ''normal'' component of the fluid is the thermalized matter in common sense, while the ''superfluid'' part consists of long wavelength (chiral) fermionic states moving independently. We use the bosonization procedure with a finite cut-off and obtain a dynamical axion-like field out of the chiral fermionic modes. Then we use relativistic hydrodynamics for macroscopic description of the effective theory obtained after the bosonization. Finally, solving the hydrodynamic equations in gradient expansion, we find that in the presence of external electromagnetic fields the motion of the ''superfluid'' component gives rise to the chiral magnetic, chiral electric and dipole wave effects. Latter two effects are specific for a two-component fluid, which provides us with crucial experimental tests of the model. By considering probe quarks one can show that the fermionic spectrum at the intermediate temperatures (T{sub c}
Shortcut to a Fermi-Degenerate Gas of Molecules via Cooperative Association
Dannenberg, O; Suominen, K A; Dannenberg, Olavi; Mackie, Matt; Suominen, Kalle-Antti; 10.1103/.91.210404
2003-01-01
The creation of a Fermi-degenerate gas molecules using either photoassociation or the Feshbach resonance is theoretically examined. This problem raises an interest because, unlike bosons, fermions in general do not behave cooperatively, so that the collective association of, say, two million atoms into one million molecules is not to be expected. Nevertheless, we find that the coupled Fermi system displays collective Rabi-like oscillations and adiabatic passage between atoms and molecules, thereby mimicking Bose-Einstein statistics. Cooperative association of a degenerate mixture of Bose and Fermi gases could therefore serve as a shortcut to a degenerate gas of Fermi molecules.
Bouffard, Karen
1999-09-01
"Fermi" questions are a popular component of most Physics Olympics meets. Asking students to make a reasonable assumption about a problem and give answers in terms of order of magnitude is not only a great challenge for a competition, but is also a valued teaching strategy in the classroom.
Solares, H A Ayala; Hüntemeyer, P
2015-01-01
The Fermi Bubbles, which comprise two large and homogeneous regions of spectrally hard gamma-ray emission extending up to $55^{o}$ above and below the Galactic Center, were first noticed in GeV gamma-ray data from the Fermi Telescope in 2010. The mechanism or mechanisms which produce the observed hard spectrum are not understood. Although both hadronic and lep- tonic models can describe the spectrum of the bubbles, the leptonic model can also explain similar structures observed in microwave data from the WMAP and Planck satellites. Recent publications show that the spectrum of the Fermi Bubbles is well described by a power law with an exponential cutoff in the energy range of 100MeV to 500GeV. Observing the Fermi Bubbles at higher gamma-ray energies will help constrain the origin of the bubbles. A steeper cutoff will favor a leptonic model. The High Altitude Water Cherenkov (HAWC) Observatory, located 4100m above sea level in Mexico, is designed to measure high-energy gamma rays between 100GeV to 100TeV. With...
Institute of Scientific and Technical Information of China (English)
LI Shichun
2004-01-01
Based on the Thomas-Fermi-Dirac-Cheng model, atomic phase diagram or electron density versus atomic radius diagram describing the interaction properties of atoms of different kinds in equilibrium state is developed. Atomic phase diagram is established based on the two-atoms model. Besides atomic radius, electron density and continuity condition for electron density on interfaces between atoms, the lever law of atomic phase diagram involving other physical parameters is taken into account, such as the binding energy, for the sake of simplicity.
Generation of dark-bright soliton trains in superfluid-superfluid counterflow.
Hamner, C; Chang, J J; Engels, P; Hoefer, M A
2011-02-11
The dynamics of two penetrating superfluids exhibit an intriguing variety of nonlinear effects. Using two distinguishable components of a Bose-Einstein condensate, we investigate the counterflow of two superfluids in a narrow channel. We present the first experimental observation of trains of dark-bright solitons generated by the counterflow. Our observations are theoretically interpreted by three-dimensional numerical simulations for the coupled Gross-Pitaevskii equations and the analysis of a jump in the two relatively flowing components' densities. Counterflow-induced modulational instability for this miscible system is identified as the central process in the dynamics. PMID:21405475
Orbital angular momentum and spectral flow in two-dimensional chiral superfluids.
Tada, Yasuhiro; Nie, Wenxing; Oshikawa, Masaki
2015-05-15
We study the orbital angular momentum (OAM) L_{z} in two-dimensional chiral (p_{x}+ip_{y})^{ν}-wave superfluids (SFs) of N fermions on a disk at zero temperature, in terms of spectral asymmetry and spectral flow. It is shown that L_{z}=νN/2 for any integer ν, in the Bose-Einstein condensation regime. In contrast, in the BCS limit, while the OAM is L_{z}=N/2 for the p+ip-wave SF, for chiral SFs with ν≥2, the OAM is remarkably suppressed as L_{z}=N×O(Δ_{0}/ϵ_{F})≪N, where Δ_{0} is the gap amplitude and ϵ_{F} is the Fermi energy. We demonstrate that the difference between the p+ip-wave SF and the other chiral SFs in the BCS regimes originates from the nature of edge modes and related depairing effects. PMID:26024177
Gamow-Teller strength functions of superfluid odd nuclei and neutrino capture reactions
International Nuclear Information System (INIS)
The charge-exchange excitations of superfluid odd-A nuclei are studied within the framework of the self-consistent finite Fermi-system theory. The pairing blocking effect due to the odd quasiparticle, the effective NN-interactions both in the particle-hole (ph) and particle-particle (pp) channel, and also the ph-continuum are taken into account. Gamow-Teller strength functions of 71Ga, 115In and 19F nuclei are calculated and compared with those extracted from experimental spectra of (p,n) reactions. The total capture cross sections of the reactor electron antineutrinos are calculated (assuming complete μe-bar→μe conversion), as well as the solar neutrino capture rates for the 71Ga and 115In+19F detectors. Uncertainties regarding nuclear structure information involved in these calculations are discussed. (authors) 55 refs., 4 figs., 3 tabs
International Nuclear Information System (INIS)
We propose a model for the quasiparticles of superfluid 4He which describes both phonons and rotons in a unified way. The theory is based on the fact that the thermal de Broglie wavelengths of the atoms overlap each other. This allows us to treat superfluid 4He as a continuous medium at all length scales. Then the parameters of the continouous medium (density, pressure, and velocity) can be given a probabilistic value at each point in space. The quasiparticles of superfluid 4He are small fluctuations in these parameters; the frequency and wave vector of a fluctuation correspond to the energy and momentum of the quasiparticle, respectively. Using the Lagrange formalism we derive equations for the potential associated with these fluctuations, and this leads to a generalized wave equation. From the Hamiltonian formalism we derive a system of equations for the variables of a continuous medium, and show that in the general case there is a non-local dependence between pressure and density. Applying the methods of the mechanics of continuous media, we calculate the creation probabilities for both phonons and rotons by phonons in a solid, in a unified way. This theory explains why R- rotons are not created by a heater. The theory is compared with those of others, and the results with experiments
Hydrodynamics of normal and superfluid polar liquids. Sound propagation
International Nuclear Information System (INIS)
Hydrodynamic equations for normal and superfluid liquids, possessing spontaneous electric polarization, are obtained using the phenomenological approach. It is shown that sound wave propagation is followed by electric field oscillations. Corrections to speeds of the first and second sounds in normal and superfluid polar liquids are calculated
Some new NMR effects in superfluid 3He--A
International Nuclear Information System (INIS)
Longitudinal and transverse satellite lines have been observed by CW techniques in superfluid 3He-A under a variety of experimental conditions. A new metastable mode has been observed in superfluid 3He-A using pulsed NMR techniques. The frequency shift of this mode is related to the frequency shift of the transverse satellite line
Generalized equation of state for cold superfluid neutron stars
Chamel, N.; Pearson, J M; Goriely, S
2010-01-01
Mature neutron stars are expected to contain various kinds of superfluids in their interiors. Modeling such stars requires the knowledge of the mutual entrainment couplings between the different condensates. We present a unified equation of state describing the different regions of a neutron star with superfluid neutrons and superconducting protons in its core.
A two-dimensional Fermi gas in the BEC-BCS crossover
Energy Technology Data Exchange (ETDEWEB)
Ries, Martin Gerhard
2016-01-21
This thesis reports on the preparation of a 2D Fermi gas in the BEC-BCS crossover and the observation of the BKT transition into a quasi long-range ordered superfluid phase. The pair momentum distribution of the gas is probed by means of a matter-wave focusing technique which relies on time-of-flight evolution in a weak harmonic potential. This distribution holds the coherence properties of the gas. The quasi long-range ordered phase manifests itself as a sharp low-momentum peak. The temperature where it forms is identified as the transition temperature. By tuning the temperature and the interaction strength, the phase diagram of the 2D Fermi gas in the BEC-BCS crossover is mapped out. The phase coherence is investigated in a self-interference experiment. Furthermore, algebraic decay of correlations is observed in the trap average of the first order correlation function, which is obtained from the Fourier transform of the pair momentum distribution. This is in qualitative agreement with predictions of homogeneous theory for the superfluid phase in a 2D gas. The presented results provide a foundation for future experimental and theoretical studies of strongly correlated 2D Fermi gases. They might thus help to elucidate complex systems such as the electron gas in high-T{sub c} superconductors.
Tarasov, Alexander N
2013-01-01
A generalized non-relativistic Fermi-liquid approach was used to find analytical formulas for temperatures $T_{c,1}(n,H)$ and $T_{c,2}(n,H)$ (which are functions nonlinear of density n and linear of magnetic field H) of phase transitions in spatially uniform dense pure neutron matter from normal to superfluid states with spin-triplet p-wave pairing (similar to anisotropic superfluid phases $^3He-A_{1}$ and $^3He-A_{2}$) in steady and homogeneous strong magnetic field (but $|\\mu_{n}| H\\ll E_{c}<\\varepsilon_{F}(n)$, where $\\mu_{n}$ is the magnetic dipole moment of a neutron, E_{c} is the cutoff energy and $\\varepsilon_{F}(n)$ is the Fermi energy in neutron matter). General formulas for $T_{c,1,2}(n,H)$ (valid for arbitrary parametrization of the effective Skyrme interaction in neutron matter) are specified here for generalized BSk18 parametrization of the Skyrme forces (with additional terms dependent on density n) on the interval $0.3\\ n_{0}
Dai, Liang; Schmidt, Fabian
2015-01-01
Fermi Normal Coordinates (FNC) are a useful frame for isolating the locally observable, physical effects of a long-wavelength spacetime perturbation. Their cosmological application, however, is hampered by the fact that they are only valid on scales much smaller than the horizon. We introduce a generalization that we call Conformal Fermi Coordinates (CFC). CFC preserve all the advantages of FNC, but in addition are valid outside the horizon. They allow us to calculate the coupling of long- and short-wavelength modes on all scales larger than the sound horizon of the cosmological fluid, starting from the epoch of inflation until today, by removing the complications of the second order Einstein equations to a large extent, and eliminating all gauge ambiguities. As an application, we present a calculation of the effect of long-wavelength tensor modes on small scale density fluctuations. We recover previous results, but clarify the physical content of the individual contributions in terms of locally measurable ef...
Shah, Kushal; Rom-Kedar, Vered; Turaev, Dmitry
2015-01-01
A Fermi accelerator is a billiard with oscillating walls. A leaky accelerator interacts with an environment of an ideal gas at equilibrium by exchange of particles through a small hole on its boundary. Such interaction may heat the gas: we estimate the net energy flow through the hole under the assumption that the particles inside the billiard do not collide with each other and remain in the accelerator for sufficiently long time. The heat production is found to depend strongly on the type of the Fermi accelerator. An ergodic accelerator, i.e. one which has a single ergodic component, produces a weaker energy flow than a multi-component accelerator. Specifically, in the ergodic case the energy gain is independent of the hole size, whereas in the multi-component case the energy flow may be significantly increased by shrinking the hole size.
Laser cooling and control of excitations in superfluid helium
Harris, G I; Sheridan, E; Sachkou, Y; Baker, C; Bowen, W P
2015-01-01
Superfluidity is an emergent quantum phenomenon which arises due to strong interactions between elementary excitations in liquid helium. These excitations have been probed with great success using techniques such as neutron and light scattering. However measurements to-date have been limited, quite generally, to average properties of bulk superfluid or the driven response far out of thermal equilibrium. Here, we use cavity optomechanics to probe the thermodynamics of superfluid excitations in real-time. Furthermore, strong light-matter interactions allow both laser cooling and amplification of the thermal motion. This provides a new tool to understand and control the microscopic behaviour of superfluids, including phonon-phonon interactions, quantised vortices and two-dimensional quantum phenomena such as the Berezinskii-Kosterlitz-Thouless transition. The third sound modes studied here also offer a pathway towards quantum optomechanics with thin superfluid films, including femtogram effective masses, high me...
Superfluid response of two-dimensional parahydrogen clusters in confinement
International Nuclear Information System (INIS)
We study by computer simulations the effect of confinement on the superfluid properties of small two-dimensional (2D) parahydrogen clusters. For clusters of fewer than twenty molecules, the superfluid response in the low temperature limit is found to remain comparable in magnitude to that of free clusters, within a rather wide range of depth and size of the confining well. The resilience of the superfluid response is attributable to the “supersolid” character of these clusters. We investigate the possibility of establishing a bulk 2D superfluid “cluster crystal” phase of p-H2, in which a global superfluid response would arise from tunnelling of molecules across adjacent unit cells. The computed energetics suggests that for clusters of about ten molecules, such a phase may be thermodynamically stable against the formation of the equilibrium insulating crystal, for values of the cluster crystal lattice constant possibly allowing tunnelling across adjacent unit cells
Dark Energy and Dark Matter in a Superfluid Universe
Huang, Kerson
2013-01-01
The vacuum is filled with complex scalar fields, such as the Higgs field. These fields serve as order parameters for superfluidity (quantum phase coherence over macroscopic distances), making the entire universe a superfluid. We review a mathematical model consisting of two aspects: (a) emergence of the superfluid during the big bang; (b) observable manifestations of superfluidity in the present universe. The creation aspect requires a self-interacting scalar field that is asymptotically free, i.e., the interaction must grow from zero during the big bang, and this singles out the Halpern-Huang potential, which has exponential behavior for large fields. It leads to an equivalent cosmological constant that decays like a power law, and this gives dark energy without "fine-tuning". Quantum turbulence (chaotic vorticity) in the early universe was able to create all the matter in the universe, fulfilling the inflation scenario. In the present universe, the superfluid can be phenomenologically described by a nonline...
Nonlinear hydrodynamic equations for superfluid helium in aerogel
International Nuclear Information System (INIS)
Aerogel in superfluids is studied very intensively during last decade. The importance of these systems is connected to the fact that this allows to investigate the influence of impurities on superfluidity. We have derived for the first time nonlinear hydrodynamic equations for superfluid helium in aerogel. These equations are generalization of McKenna et al. equations for nonlinear hydrodynamics case and could be used to study sound propagation phenomena in aerogel-superfluid system, in particular--to study sound conversion phenomena. We have obtained two alternative sets of equations, one of which is a generalization of a traditional set of nonlinear hydrodynamics equations for the case of an aerogel-superfluid system and, the other one represents a la Putterman equations (equation for v→s is replaced by equation for A→=((ρn)/(ρσ))w→, where w→=v→n-v→s)
Acoustic properties of superfluid 3He in 97% aerogel
International Nuclear Information System (INIS)
Superfluid 3He in silica aerogel provides a unique system for studying the effect of quenched disorder in the unconventional superfluid. We have performed longitudinal ultrasound (5.7 MHz) attenuation and sound velocity measurements of the superfluid 3He in 97% porosity aerogel. The attenuation and sound velocity were determined by direct propagation of sound pulses through the medium in a wide range of temperatures, down to 400 μK. The superfluid transition, marked by the increase in sound velocity, is substantially suppressed from that in 98% aerogel used in most of studies. The superfluid fraction determined from the sound velocity is less than 0.02 even at the lowest temperature.
A smooth polaron-molecule crossover in a Fermi system
Edwards, D.M.
2013-01-01
The problem of a single down spin particle interacting with a Fermi sea of up spin particles is of current interest in the field of cold atoms. The Hubbard model, appropriate to atoms in an optical lattice potential, is considered in parallel with a gas model. As the strength of an attractive short-range interaction is increased there is a crossover from "polaron" behaviour, in which the Fermi sea is weakly perturbed, to "molecule" behaviour in which the down spin particle is bound to a singl...
International Nuclear Information System (INIS)
The Fermi surface of niobium has been investigated using the de Haas-van Alphen effect. Data were taken at temperatures as low as .3 K and in fields as high as 130 kG. An on-line minicomputer was used to Fourier transform the digitized signals. Many new extremal area data have been obtained including oscillations associated with the previously unobserved Gamma-centered hole octahedron and Gamma and N centered orbits on the so called jungle gym. An additional set of signals has been observed near [100] which are thought to be a result of magnetic breakdown between the second zone octahedron and third zone jungle gym. A separate low frequency signal was observed and is believed to be a result of magnetic breakdown induced quantum interference oscillations. Anisotropies of the cyclotron effective mass have been determined for many orbits on all three of the Fermi surface sheets. Finally, the area data has been used to parametrize the Fermi surface in terms of scattering phase shifts in a KKR band structure formalism
Oscillations of dissipative superfluid neutron stars
International Nuclear Information System (INIS)
We investigate the oscillations of slowly rotating superfluid stars, taking into account the vortex-mediated mutual friction force that is expected to be the main damping mechanism in mature neutron star cores. Working to linear order in the rotation of the star, we consider both the fundamental f-modes and the inertial r-modes. In the case of the (polar) f-modes, we work out an analytic approximation of the mode which allows us to write down a closed expression for the mutual friction damping time scale. The analytic result is in good agreement with previous numerical results obtained using an energy integral argument. We extend previous work by considering the full range of permissible values for the vortex drag, e.g. the friction between each individual vortex and the electron fluid. This leads to the first ever results for the f-mode in the strong drag regime. Our estimates provide useful insight into the dependence on, and relevance of, various equation of state parameters. In the case of the (axial) r-modes, we confirm the existence of two classes of modes. However, we demonstrate that only one of these sets remains purely axial in more realistic neutron star models. Our analysis lays the foundation for companion studies of the mutual friction damping of the r-modes at second order in the slow-rotation approximation, the first time evolutions for superfluid neutron star perturbations and also the first detailed attempt at studying the dynamics of superfluid neutron stars with both a relative rotation between the components and mutual friction.
Superfluid Kubo Formulas from Partition Function
Chapman, Shira; Oz, Yaron
2014-01-01
Linear response theory relates hydrodynamic transport coefficients to equilibrium retarded correlation functions of the stress-energy tensor and global symmetry currents in terms of Kubo formulas. Some of these transport coefficients are non-dissipative and affect the fluid dynamics at equilibrium. We present an algebraic framework for deriving Kubo formulas for such thermal transport coefficients by using the equilibrium partition function. We use the framework to derive Kubo formulas for all such transport coefficients of superfluids, as well as to rederive Kubo formulas for various normal fluid systems.
Jou i Mirabent, David,
2007-01-01
La física quàntica s'enfronta a sorprenents propietats de la matèria que es donen només a nivell microscòpic i que desafien la realitat que podem observar a la nostra escala. La superfluïdesa és un fenomen quàntic a escala macroscòpica: els superfluids tenen una gran capacitat per transportar la calor o per fluir per capil·lars molt fins. Investigadors de la UAB i de la Universitat de Palerm estan treballant en millorar l'observació de les seves propietats.
Dark matter superfluid and DBI dark energy
Cai, Rong-Gen
2016-01-01
It was shown recently that, without jeopardizing the success of the $\\Lambda$CDM model on cosmic scales, the MOdified Newtonian Dynamics (MOND) can be derived as an emergent phenomenon when axion-like dark matter particles condense into superfluid on galactic scales. We propose in this letter a Dirac-Born-Infeld (DBI) dark energy conformally coupled to local matter components to solve both galactic and cosmic coincidences that the MOND critical acceleration coincides with present Hubble scale and the matter energy density coincides with dark energy density today. The cosmological evolution of DBI dark energy behaves as a freezing Chaplygin gas and approaches to a cosmological constant in the asymptotic future.
Rotary magnetic refrigerator for superfluid helium production
International Nuclear Information System (INIS)
A new rotary-magnetic refrigerator designed to obtain superfluid helium temperatures by executing a magnetic Carnot cycle is developed. A rotor containing 12 magnetic refrigerants (gadolinium-gallium-garnet) is immersed in liquid helium at 4.2 K and rotated at constant speed in a steady magnetic field distribution. Performance tests demonstrate that the new rotary refrigerator is capable of obtaining a temperature of 1.48 K. The maximum useful cooling power obtained at 1.8 K is 1.81 W which corresponds to a refrigeration efficiency of 34%
Bayonet for superfluid helium transfer in space
International Nuclear Information System (INIS)
A prototype bayonet for potential use in the SHOOT flight experiment was developed and evaluated with a low heat test apparatus. Measured heat leak of the 13 mm bayonet pair is 0.21 W at 1.8 K. Bayonets were fabricated with thin tubes which were electron beam welded to machined nose and flange pieces. Low heat leak structural integrity was provided by a 0.9 mm thickness of filament wound fiberglass-epoxy. Superfluid creep was restricted by KEL-F nose seals which form vacuum-tight extensions to the bayonet cold end pieces. Performance and leak test results are assessed
Turning bacteria suspensions into a "superfluid"
López, Héctor Matías; Douarche, Carine; Auradou, Harold; Clément, Eric
2015-01-01
The rheological response under simple shear of an active suspension of Escherichia coli is determined in a large range of shear rates and concentrations. The effective viscosity and the time scales characterizing the bacterial organization under shear are obtained. In the dilute regime, we bring evidences for a low shear Newtonian plateau characterized by a shear viscosity decreasing with concentration. In the semi-dilute regime, for particularly active bacteria, the suspension display a "super-fluid" like transition where the viscous resistance to shear vanishes, thus showing that macroscopically, the activity of pusher swimmers organized by shear, is able to fully overcome the dissipative effects due to viscous loss.
A phenomenological approach to the equation of state of a unitary Fermi gas
Indian Academy of Sciences (India)
M V N Murthy; M Brack; R K Bhaduri
2014-06-01
We propose a phenomenological approach for the equation of state of a unitary Fermi gas. The universal equation of state is parametrized in terms of Fermi–Dirac integrals. This reproduces the experimental data over the accessible range of fugacity and normalized temperature, but cannot describe the superfluid phase transition found in the MIT experiment [Ku et al, Science 335, 563 (2012)]. The most sensitive data for compressibility and specific heat at phase transition can, however, be fitted by introducing into the grand partition function a pair of complex conjugate zeros lying in the complex fugacity plane slightly off the real axis.
Coexistence of density wave and superfluid order in a dipolar Fermi gas
DEFF Research Database (Denmark)
Wu, Zhigang; Block, Jens Kusk; Bruun, Georg M.
2015-01-01
diagram. In this region, the repulsive part of the interaction drives the stripe formation and the attractive part induces the pairing, resulting in a supersolid with $p$-wave Cooper pairs aligned along the stripes. From a momentum space perspective, the stability of the supersolid phase is due...
Anisotropic superfluidity of {sup 4}He on a C{sub 36} fullerene molecule
Energy Technology Data Exchange (ETDEWEB)
Park, Sungjin; Kim, Byeongjoon; Kwon, Yongkyung, E-mail: ykwon@konkuk.ac.kr [Division of Quantum Phases and Devices, School of Physics, Konkuk University, Seoul 143-701 (Korea, Republic of)
2015-09-14
We have performed path-integral Monte Carlo calculations to study the adsorption of {sup 4}He atoms on two different C{sub 36} isomers with the D{sub 6h} and the D{sub 2d} symmetries. The radial {sup 4}He density distributions reveal layer-by-layer growth with the first layer being located at a distance of ∼5.5 Å from the C{sub 36} molecular center and the second layer at ∼8.3 Å. From the angular density profiles of {sup 4}He, we find different quantum states as the number of {sup 4}He adatoms N varies. For N = 20, we observe commensurate solid structures on both D{sub 6h} and D{sub 2d} isomers, where each of 8 hexagon and 12 pentagon centers of the fullerene surfaces is occupied by a single {sup 4}He atom. The second-layer promotion starts beyond N = 38 on both isomers, where a compressible incommensurate structure is observed on the D{sub 6h} isomer and another commensurate structure on D{sub 2d}. Between N = 20 and N = 38, the {sup 4}He monolayer on D{sub 6h} shows several distinct rings of delocalized {sup 4}He atoms along with strongly anisotropic superfluid responses at low temperatures, while isotropic but weak superfluid responses are observed in the {sup 4}He layer on D{sub 2d}.
Anisotropic superfluidity of 4He on a C36 fullerene molecule
International Nuclear Information System (INIS)
We have performed path-integral Monte Carlo calculations to study the adsorption of 4He atoms on two different C36 isomers with the D6h and the D2d symmetries. The radial 4He density distributions reveal layer-by-layer growth with the first layer being located at a distance of ∼5.5 Å from the C36 molecular center and the second layer at ∼8.3 Å. From the angular density profiles of 4He, we find different quantum states as the number of 4He adatoms N varies. For N = 20, we observe commensurate solid structures on both D6h and D2d isomers, where each of 8 hexagon and 12 pentagon centers of the fullerene surfaces is occupied by a single 4He atom. The second-layer promotion starts beyond N = 38 on both isomers, where a compressible incommensurate structure is observed on the D6h isomer and another commensurate structure on D2d. Between N = 20 and N = 38, the 4He monolayer on D6h shows several distinct rings of delocalized 4He atoms along with strongly anisotropic superfluid responses at low temperatures, while isotropic but weak superfluid responses are observed in the 4He layer on D2d
Dirac and Weyl rings in three-dimensional cold-atom optical lattices
Xu, Yong; Zhang, Chuanwei
2016-06-01
Recently three-dimensional topological quantum materials with gapless energy spectra have attracted considerable interest in many branches of physics. Besides the celebrated example, Dirac and Weyl points which possess gapless point structures in the underlying energy dispersion, the topologically protected gapless spectrum, can also occur along a ring, named Dirac and Weyl nodal rings. Ultracold atomic gases provide an ideal platform for exploring new topological materials with designed symmetries and dispersion. However, whether Dirac and Weyl rings can exist in the single-particle spectrum of cold atoms remains elusive. Here we propose a realistic model for realizing Dirac and Weyl rings in the single-particle band dispersion of a cold-atom optical lattice. Our scheme is based on a previously experimentally implemented Raman coupling setup for realizing spin-orbit coupling. Without the Zeeman field, the model preserves both pseudo-time-reversal and inversion symmetries, allowing Dirac rings. The Dirac rings split into Weyl rings with a Zeeman field that breaks the pseudo-time-reversal symmetry. We examine the superfluidity of attractive Fermi gases in this model and also find Dirac and Weyl rings in the quasiparticle spectrum.
Theory of superfluidity macroscopic quantum waves
International Nuclear Information System (INIS)
A new description of superfluidity is proposed, based upon the fact that Bogoliubov's theory of superfluidity exhibits some so far unsuspected macroscopic quantum waves (MQWs), which have a topological nature and travel within the fluid at subsonic velocities. To quantize the bounded quasi-particles the field theoretic version of the Bohr-Sommerfeld quantization rule, is employed and also resort to a variational computation. In an instantaneous configuration the MQWs cut the condensate into blocks of phase, providing, by analogy with ferromagnetism, a nice explanation of what could be the lambda-transition. A crude estimate of the critical temperature gives T sub(c) approximately equal to 2-4K. An attempt is made to understand Tisza's two-fluid model in terms of the MQWs, and we rise the conjecture that they play an important role in the motion of second. We present also a qualitative prediction concerning to the behavior of the 'phononroton' peak below 1.0K, and propose two experiments to look for MQWs
Large quantum superpositions of a nanoparticle immersed in superfluid helium
Lychkovskiy, O.
2016-06-01
Preparing and detecting spatially extended quantum superpositions of a massive object comprises an important fundamental test of quantum theory. These quantum states are extremely fragile and tend to quickly decay into incoherent mixtures due to the environmental decoherence. Experimental setups considered up to date address this threat in a conceptually straightforward way—by eliminating the environment, i.e., by isolating an object in a sufficiently high vacuum. We show that another option exists: decoherence is suppressed in the presence of a strongly interacting environment if this environment is superfluid. Indeed, as long as an object immersed in a pure superfluid at zero temperature moves with a velocity below the critical one, it does not create, absorb, or scatter any excitations of the superfluid. Hence, in this idealized situation the decoherence is absent. In reality the decoherence will be present due to thermal excitations of the superfluid and impurities contaminating the superfluid. We examine various decoherence channels in the superfluid
Zero temperature holographic superfluids with two competing orders
Ran, Li; Tian, Yu; Zhang, Hongbao; Zhao, Junkun
2016-08-01
We initiate the investigation of the zero temperature holographic superfluids with two competing orders, where besides the vacuum phase, two one component superfluid phases, the coexistent superfluid phase has also been found in the anti-de Sitter soliton background for the first time. We construct the complete phase diagram in the e - μ plane by numerics, which is consistent with our qualitative analysis. Furthermore, we calculate the corresponding optical conductivity and sound speed by the linear response theory. The onset of the pole of optical conductivity at ω =0 indicates that the spontaneous breaking phase always represents the superfluid phase, and the residue of the pole is increased with the chemical potential, which is consistent with the fact that the particle density is essentially the superfluid density for zero temperature superfluids. In addition, the resulting sound speed demonstrates the nonsmoothness at the critical points as the order parameter of the condensate, which indicates that the phase transitions can also be identified by the behavior of the sound speed. Moreover, as expected from the boundary conformal field theory, the sound speed saturates to 1/√{2 } at the large chemical potential limit for our two component holographic superfluid model.
First and Second Sound Modes in a Uniform Fermi Gas
Institute of Scientific and Technical Information of China (English)
HUANG Bei-Bing; WAN Shao-Long
2009-01-01
First and second sound modes in a uniform fermionic atom gas with Feshbach resonance are investigated in the frame of a two-fluid model at finite temperature. All thermodynamic quantities are calculated for a given thermodynamic potential The analytical results for thermodynamic quantities and sound velocities in BCS and BEC limits are obtained. The numerical rcsults show that there exists a continuous interpolation for sound velocities of the first and second sound modes at fixed T/Tc between BCS and BEC limits. The existence of the second sound mode indicates the existence of superfluidity.
Chen, Jing-Yuan
2016-01-01
We develop an extension of the Landau Fermi liquid theory to systems of interacting fermions with non-trivial Berry curvature. We propose a kinetic equation and a constitutive relation for the electromagnetic current that together encode the linear response of such systems to external electromagnetic perturbations, to leading and next-to-leading orders in the expansion over the frequency and wave number of the perturbations. We analyze the Feynman diagrams in a large class of interacting quantum field theories and show that, after summing up all orders in perturbation theory, the current-current correlator exactly matches with the result obtained from the kinetic theory.
Dynamical alpha-type correlations in deformed superfluid nuclei
International Nuclear Information System (INIS)
By including an adequate four-particle interaction, correlations between the proton and neutron fluids in deformed nuclei are induced. As a result, superfluidities of the two nuclear systems may be generated by one another and the phase structure is enriched by a new superfluid phase dominated by alpha-type correlations. Among the consequences upon the nuclear structure and dynamics figure the prediction of new bands of elementary excitations and the increase of superfluid enhancement factors for alpha and pair transfer reactions. (author). 18 refs, 2 figs, 1 tab
Testing of accelerator dipoles in pressurized superfluid helium
International Nuclear Information System (INIS)
Two superconducting accelerator dipole magnets, with different internal construction features, have been tested in pressurized superfluid helium (1.8K, 1.2 atmosphere) as well as in regular pool boiling helium (4.4K, 1.2 atmosphere) helium. The coils of one magnet were moderately pre-stressed, and 4.2K design performance was rapidly achieved in the superfluid. The other magnet had very low coil pre-stress, reduced helium ventilation, and displayed degraded performance, even in the superfluid helium
Superfluid and antiferromagnetic phases in ultracold fermionic quantum gases
Energy Technology Data Exchange (ETDEWEB)
Gottwald, Tobias
2010-08-27
In this thesis several models are treated, which are relevant for ultracold fermionic quantum gases loaded onto optical lattices. In particular, imbalanced superfluid Fermi mixtures, which are considered as the best way to realize Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) states experimentally, and antiferromagnetic states, whose experimental realization is one of the next major goals, are examined analytically and numerically with the use of appropriate versions of the Hubbard model. The usual Bardeen-Cooper-Schrieffer (BCS) superconductor is known to break down in a magnetic field with a strength exceeding the size of the superfluid gap. A spatially inhomogeneous spin-imbalanced superconductor with a complex order parameter known as FFLO-state is predicted to occur in translationally invariant systems. Since in ultracold quantum gases the experimental setups have a limited size and a trapping potential, we analyze the realistic situation of a non-translationally invariant finite sized Hubbard model for this purpose. We first argue analytically, why the order parameter should be real in a system with continuous coordinates, and map our statements onto the Hubbard model with discrete coordinates defined on a lattice. The relevant Hubbard model is then treated numerically within mean field theory. We show that the numerical results agree with our analytically derived statements and we simulate various experimentally relevant systems in this thesis. Analogous calculations are presented for the situation at repulsive interaction strength where the N'eel state is expected to be realized experimentally in the near future. We map our analytical results obtained for the attractive model onto corresponding results for the repulsive model. We obtain a spatially invariant unit vector defining the direction of the order parameter as a consequence of the trapping potential, which is affirmed by our mean field numerical results for the repulsive case. Furthermore, we observe
Superconductor-Insulator Transition and Fermi-Bose Crossovers
Loh, Yen Lee; Randeria, Mohit; Trivedi, Nandini; Chang, Chia-Chen; Scalettar, Richard
2016-04-01
The direct transition from an insulator to a superconductor (SC) in Fermi systems is a problem of long-standing interest, which necessarily goes beyond the standard BCS paradigm of superconductivity as a Fermi surface instability. We introduce here a simple, translationally invariant lattice fermion model that undergoes a SC-insulator transition (SIT) and elucidate its properties using analytical methods and quantum Monte Carlo simulations. We show that there is a fermionic band insulator to bosonic insulator crossover in the insulating phase and a BCS-to-BEC crossover in the SC. The SIT is always found to be from a bosonic insulator to a BEC-like SC, with an energy gap for fermions that remains finite across the SIT. The energy scales that go critical at the SIT are the gap to pair excitations in the insulator and the superfluid stiffness in the SC. In addition to giving insight into important questions about the SIT in solid-state systems, our model should be experimentally realizable using ultracold fermions in optical lattices.
Harmonically trapped quasi-two-dimensional Fermi gases with synthetic spin-orbit coupling
Wang, JingKun; Chen, JinGe; Chen, KeJi; Yi, Wei; Zhang, Wei
2016-09-01
We study the properties of spin-orbit coupled and harmonically trapped quasi-two-dimensional Fermi gas with tunable s-wave interaction between the two spin species. We adapt an effective two-channel model which takes the excited states occupation in the strongly confined axial direction into consideration by introducing dressed molecules in the closed channel, and use a Bogoliubovde Gennes (BdG) formalism to go beyond local density approximation. We find that both the in-trap phase structure and density distribution can be significantly modified near a wide Feshbach resonance compared with the single-channel model without the dressed molecules. Our findings will be helpful for the experimental search for the topological superfluid phase in ultracold Fermi gases.
Superfluid helium-4 interferometers: construction and experiments
Joshi, Aditya Ajit
This dissertation has two main goals: to highlight some new results in the field of superfluid 4He interferometry and to provide an in-depth, "hands-on" guide to the physics, design, construction, testing and operation of a continuously operating, fluxlocked 4 He dc-SHeQUID (Superfluid Helium Quantum Interference Device). Many of these topics haven't really been addressed in writing and the hapless new experimenter seeking to develop a SHeQUID is generally forced to reinvent the wheel rather than start at the frontier and push it forward. We would like to prevent that by making this a comprehensive guide to building and operating SHeQUIDs. We have optimized the fabrication of the nanoscale aperture arrays that are the very heart of the SHeQUID and resolved long-standing issues with their durability and long-term usability. A detailed report on this should assist in avoiding the many pitfalls that await those who fabricate and use these aperture arrays. We have constructed a new, modular SHeQUID that is designed to be easily adaptable to a wide array of proposed experiments without the necessity of rebuilding and reassembling key components like the displacement transducer. We have automated its working as a continuously operating, linearized (flux-locked) interferometer by using the so-called "chemical potential battery" in conjunction with a feedback system. We have also constructed a new reorientation system that is several orders of magnitude quieter than its predecessors. Together, these developments have allowed us to measure a changing rotation field in real time, a new development for this kind of device. We have also developed a module that allows control of the reorientation stage by automated data-taking software for investigating long-term drifts (by safely sweeping the stage back and forth). We have also investigated the chemical potential battery in further detail and report some fascinating nonlinear mode locking phenomena that have important
International Nuclear Information System (INIS)
Making use of the operator product expansion, we derive a general class of sum rules for the imaginary part of the single-particle self-energy of the unitary Fermi gas. The sum rules are analyzed numerically with the help of the maximum entropy method, which allows us to extract the single-particle spectral density as a function of both energy and momentum. These spectral densities contain basic information on the properties of the unitary Fermi gas, such as the dispersion relation and the superfluid pairing gap, for which we obtain reasonable agreement with the available results based on quantum Monte-Carlo simulations
This FERMI multi-chip module contains five million transistors. 25 000 of these modules will handle the flood of information through parts of the ATLAS and CMS detectors at the LHC. To select interesting events for recording, crucial decisions are taken before the data leaves the detector. FERMI modules are being developed at CERN in partnership with European industry.
Fermi Communications and Public Outreach
Cominsky, L
2015-01-01
The Sonoma State University (SSU) Education and Public Outreach (E/PO) group participates in the planning and execution of press conferences that feature noteworthy Fermi discoveries, as well as supporting social media and outreach websites. We have also created many scientific illustrations for the media, tools for amateur astronomers for use at star parties, and have given numerous public talks about Fermi discoveries.
The extension of radiative viscosity to superfluid matter
Pi, Chun-Mei; Yang, Shu-Hua; Zheng, Xiao-Ping
2010-01-01
The radiative viscosity of superfluid $npe$ matter is studied, and it is found that to the lowest order of $\\delta \\mu/T$ the ratio of radiative viscosity to bulk viscosity is the same as that of the normal matter.
Identifying a Superfluid Reynolds Number via Dynamical Similarity
Reeves, M. T.; Billam, T. P.; Anderson, B. P.; Bradley, A. S.
2015-04-01
The Reynolds number provides a characterization of the transition to turbulent flow, with wide application in classical fluid dynamics. Identifying such a parameter in superfluid systems is challenging due to their fundamentally inviscid nature. Performing a systematic study of superfluid cylinder wakes in two dimensions, we observe dynamical similarity of the frequency of vortex shedding by a cylindrical obstacle. The universality of the turbulent wake dynamics is revealed by expressing shedding frequencies in terms of an appropriately defined superfluid Reynolds number, Res, that accounts for the breakdown of superfluid flow through quantum vortex shedding. For large obstacles, the dimensionless shedding frequency exhibits a universal form that is well-fitted by a classical empirical relation. In this regime the transition to turbulence occurs at Res≈0.7 , irrespective of obstacle width.
Stability of superfluid vortices in dense quark matter
Alford, Mark G.; Mallavarapu, S. Kumar; Vachaspati, Tanmay; Windisch, Andreas
2016-04-01
Superfluid vortices in the color-flavor-locked (CFL) phase of dense quark matter are known to be energetically disfavored relative to well-separated triplets of so-called semi-superfluid color flux tubes. However, the short-range interaction (metastable versus unstable) has not been established. In this paper we perform numerical calculations using the effective theory of the condensate field, mapping the regions in the parameter space of coupling constants where the vortices are metastable versus unstable. For the case of zero-gauge coupling we analytically identify a candidate for the unstable mode and show that it agrees well with the results of the numerical calculations. We find that in the region of the parameter space that seems likely to correspond to real-world CFL quark matter the vortices are unstable, indicating that if such matter exists in neutron star cores it is very likely to contain semi-superfluid color flux tubes rather than superfluid vortices.
Stability of superfluid vortices in dense quark matter
Alford, Mark G; Vachaspati, Tanmay; Windisch, Andreas
2016-01-01
Superfluid vortices in the color-flavor-locked (CFL) phase of dense quark matter are known to be energetically disfavored relative to well-separated triplets of "semi-superfluid" color flux tubes. However, the short-range interaction (metastable versus unstable) has not been established. In this paper we perform numerical calculations using the effective theory of the condensate field, mapping the regions in the parameter space of coupling constants where the vortices are metastable versus unstable. For the case of zero gauge coupling we analytically identify a candidate for the unstable mode, and show that it agrees well with the results of the numerical calculations. We find that in the region of the parameter space that seems likely to correspond to real-world CFL quark matter the vortices are unstable, indicating that if such matter exists in neutron star cores it is very likely to contain semi-superfluid color flux tubes rather than superfluid vortices.
Observation of quantized circulation in rotating superfluid 4He
International Nuclear Information System (INIS)
The quantized circulation of rotating superfluid helium 4 was measured by monitoring the time rate of precession of the plane of vibration of a vibrating wire lying along the cylindrical axis of the container
Physical vacuum is a special superfluid medium
Sbitnev, Valeriy I
2015-01-01
The Navier-Stokes equation contains two terms which have been subjected to slight modification: (a) the viscosity term depends of time (the viscosity in average on time is zero, but its variance is non-zero); (b) the pressure gradient contains an added term describing the quantum entropy gradient multiplied by the pressure. Owing to these modifications, the Navier-Stokes equation can be reduced to the Schr\\"odinger equation describing behavior of a particle into the vacuum being as a superfluid medium. Vortex structures arising in this medium show infinitely long life owing to zeroth average viscosity. The non-zero variance describes exchange of the vortex energy with zero-point energy of the vacuum. Radius of the vortex trembles around some average value. This observation sheds the light to the Zitterbewegung phenomenon. The long-lived vortex has a non-zero core where the vortex velocity vanishes.
Superfluid dynamics of 258Fm fission
Scamps, Guillaume; Lacroix, Denis
2015-01-01
Theoretical description of nuclear fission remains one of the major challenges of quantum many-body dynamics. The slow, mostly adiabatic motion through the fission barrier is followed by a fast, non-adiabatic descent of the potential between the fragments. The latter stage is essentially unexplored. However, it is crucial as it generates most of the excitation energy in the fragments. The superfluid dynamics in the latter stage of fission is obtained with the time-dependent Hartree-Fock theory including BCS dynamical pairing correlations. The fission modes of the 258Fm nucleus are studied. The resulting fission fragment characteristics show a good agreement with experimental data. Quantum shell effects are shown to play a crucial role in the dynamics and formation of the fragments. The importance of quantum fluctuations beyond the independent particle/quasi-particle picture is underlined and qualitatively studied.
On superconductivity and superfluidity a scientific autobiography
Ginzburg, Vitaly L
2009-01-01
This book presents the Nobel Laureate Vitaly Ginzburg's views on the development in the field of superconductivity. It contains a selection of Ginzburg's key writings, including his amended version of the Nobel lecture in Physics 2003. Also included are an expanded autobiography, which was written for the Nobel Committee, an article entitled "A Scientific Autobiography: An Attempt," a fundamental article co-written with L.D. Landau entitled "To the theory of superconductivity," an expanded review article "Superconductivity and superfluidity (what was done and what was not done)," and some newly written short articles about superconductivity and related subjects. So, in toto, presented here are the personal contributions of Ginzburg, that resulted in the Nobel Prize, in the context of his scientific biography.
On superconductivity and superfluidity. A scientific autobiography
International Nuclear Information System (INIS)
This book presents the Nobel Laureate Vitaly Ginzburg's views on the development in the field of superconductivity. It contains a selection of Ginzburg's key writings, including his amended version of the Nobel lecture in Physics 2003. Also included are an expanded autobiography, which was written for the Nobel Committee, an article entitled ''A Scientific Autobiography: An Attempt,'' a fundamental article co-written with L.D. Landau entitled ''To the theory of superconductivity,'' an expanded review article ''Superconductivity and superfluidity (what was done and what was not done),'' and some newly written short articles about superconductivity and related subjects. So, in toto, presented here are the personal contributions of Ginzburg, that resulted in the Nobel Prize, in the context of his scientific biography. (orig.)
The stability of a superfluid rotating jet
International Nuclear Information System (INIS)
We consider the linear stability of a cylindrical rotating jet of pure superfluid held together by surface tension. A necessary and sufficient condition for stability to axisymmetric disturbances is derived which corresponds to that of a classical inviscid fluid. For axisymmetric disturbances we find that the vortex tension does not affect the range of unstable axial wave numbers, only the temporal growth rate and the most critical wave number. A sufficient condition for the stability of a general disturbance is derived which corresponds to that of a classical inviscid fluid. We find for non-axisymmetric disturbances, that the vortex tension increases the range of unstable wave numbers. The temporal growth rates of the unstable azimuthal modes increase with vortex tension
Quench from Mott Insulator to Superfluid
Energy Technology Data Exchange (ETDEWEB)
Zurek, Wojciech H. [Los Alamos National Laboratory; Dziarmaga, Jacek [Instytut Fizyki Uniwersytetu Jagiello´nskiego; Tylutki, Marek [Instytut Fizyki Uniwersytetu Jagiello´nskiego
2012-06-01
We study a linear ramp of the nearest-neighbor tunneling rate in the Bose-Hubbard model driving the system from the Mott insulator state into the superfluid phase. We employ the truncated Wigner approximation to simulate linear quenches of a uniform system in 1...3 dimensions, and in a harmonic trap in 3 dimensions. In all these setups the excitation energy decays like one over third root of the quench time. The -1/3 scaling is explained by an impulse-adiabatic approximation - a variant of the Kibble-Zurek mechanism - describing a crossover from non-adiabatic to adiabatic evolution when the system begins to keep pace with the increasing tunneling rate.
Superfluid 4He dynamics beyond quasiparticle excitations
Beauvois, K.; Campbell, C. E.; Dawidowski, J.; Fâk, B.; Godfrin, H.; Krotscheck, E.; Lauter, H.-J.; Lichtenegger, T.; Ollivier, J.; Sultan, A.
2016-07-01
The dynamics of superfluid 4He at and above the Landau quasiparticle regime is investigated by high-precision inelastic neutron scattering measurements of the dynamic structure factor. A highly structured response is observed above the familiar phonon-maxon-roton spectrum, characterized by sharp thresholds for phonon-phonon, maxon-roton, and roton-roton coupling processes. The experimental dynamic structure factor is compared to the calculation of the same physical quantity by a dynamic many-body theory including three-phonon processes self-consistently. The theory is found to provide a quantitative description of the dynamics of the correlated bosons for energies up to about three times that of the Landau quasiparticles.
Geometric origin of superfluidity in the Lieb lattice flat band
Julku, Aleksi; Peotta, Sebastiano; Vanhala, Tuomas; Kim, Dong-Hee; Törmä, Päivi
2016-01-01
The ground state and transport properties of the Lieb lattice flat band in the presence of an attractive Hubbard interaction are considered. It is shown that the superfluid weight can be large even for an isolated and strictly flat band. Moreover the superfluid weight is proportional to the interaction strength and to the quantum metric, a band structure invariant obtained from the flat-band Bloch functions. These predictions are amenable to verification with ultracold gases and may explain t...
Holographic superfluid flows with a localized repulsive potential
Ishibashi, Akihiro; Okamura, Takashi
2016-01-01
We investigate a holographic model of superfluid flows with an external repulsive potential. When the strength of the potential is sufficiently weak, we analytically construct two steady superfluid flow solutions. As the strength of the potential is increased, the two solutions merge into a single critical solution at a critical strength, and then disappear above the critical value, as predicted by a saddle-node bifurcation theory. We also analyze the spectral function of fluctuations around the solutions under a certain decoupling approximation.
Energy spectra of finite temperature superfluid helium-4 turbulence
International Nuclear Information System (INIS)
A mesoscopic model of finite temperature superfluid helium-4 based on coupled Langevin-Navier-Stokes dynamics is proposed. Drawing upon scaling arguments and available numerical results, a numerical method for designing well resolved, mesoscopic calculations of finite temperature superfluid turbulence is developed. The application of model and numerical method to the problem of fully developed turbulence decay in helium II, indicates that the spectral structure of normal-fluid and superfluid turbulence is significantly more complex than that of turbulence in simple-fluids. Analysis based on a forced flow of helium-4 at 1.3 K, where viscous dissipation in the normal-fluid is compensated by the Lundgren force, indicate three scaling regimes in the normal-fluid, that include the inertial, low wavenumber, Kolmogorov k−5/3 regime, a sub-turbulence, low Reynolds number, fluctuating k−2.2 regime, and an intermediate, viscous k−6 range that connects the two. The k−2.2 regime is due to normal-fluid forcing by superfluid vortices at high wavenumbers. There are also three scaling regimes in the superfluid, that include a k−3 range that corresponds to the growth of superfluid vortex instabilities due to mutual-friction action, and an adjacent, low wavenumber, k−5/3 regime that emerges during the termination of this growth, as superfluid vortices agglomerate between intense normal-fluid vorticity regions, and weakly polarized bundles are formed. There is also evidence of a high wavenumber k−1 range that corresponds to the probing of individual-vortex velocity fields. The Kelvin waves cascade (the main dynamical effect in zero temperature superfluids) appears to be damped at the intervortex space scale
Interaction of phonons at superfluid helium-solid interfaces
I.N. Adamenko; Nemchenko, E. K.
2014-01-01
A new method of obtaining the interaction Hamiltonian of phonons at superfluid helium-solid interface is proposed in the work. Equations of hydrodynamic variables are obtained in terms of second quantization if helium occupies a half-space. The contributions of all processes to the heat flux from solid to superfluid helium are calculated based on the obtained Hamiltonian. The angular distribution of phonons emitted by a solid is found in different processes. It is shown that all the exit angl...
First Sound in Holographic Superfluids at Zero Temperature
Esposito, Angelo; Penco, Riccardo
2016-01-01
Within the context of AdS/CFT, the gravity dual of an s-wave superfluid is given by scalar QED on an asymptotically AdS spacetime. While this conclusion is vastly supported by numerical arguments, here we provide an analytical proof that this is indeed the case. Working at zero temperature, we explicitly find the quadratic action for the superfluid phonon at the boundary in an arbitrary number of dimensions, recovering the known dispersion relation for conformal first sound.
Minimally destructive, Doppler measurement of a quantized, superfluid flow
Kumar, A.; Anderson, N.; Phillips, W. D.; Eckel, S.; Campbell, G. K.; Stringari, S.
2015-01-01
The Doppler effect, the shift in the frequency of sound due to motion, is present in both classical gases and quantum superfluids. Here, we perform an in-situ, minimally destructive measurement, of the persistent current in a ring-shaped, superfluid Bose-Einstein condensate using the Doppler effect. Phonon modes generated in this condensate have their frequencies Doppler shifted by a persistent current. This frequency shift will cause a standing-wave phonon mode to be "dragged" along with the...
A minimal model for finite temperature superfluid dynamics
Andersson, N.; Krueger, C.; Comer, G. L.; Samuelsson, L.
2012-01-01
Building on a recently improved understanding of the problem of heat flow in general relativity, we develop a hydrodynamical model for coupled finite temperature superfluids. The formalism is designed with the dynamics of the outer core of a mature neutron star (where superfluid neutrons are coupled to a conglomerate of protons and electrons) in mind, but the main ingredients are relevant for a range of analogous problems. The entrainment between material fluid components (the condensates) an...
Buoyancy and g-modes in young superfluid neutron stars
Passamonti, A.; Andersson, N.; Ho, W.C.G.
2015-01-01
We consider the local dynamics of a realistic neutron star core, including composition gradients, superfluidity and thermal effects. The main focus is on the gravity g-modes, which are supported by composition stratification and thermal gradients. We derive the equations that govern this problem in full detail, paying particular attention to the input that needs to be provided through the equation of state and distinguishing between normal and superfluid regions. The analysis highlights a num...
Quasi-periodic oscillations in superfluid magnetars
Passamonti, A.; Lander, S. K.
2014-02-01
We study the time evolution of axisymmetric oscillations of superfluid magnetars with a poloidal magnetic field and an elastic crust, working in Newtonian gravity. Extending earlier models, we study the effects of composition gradients and entrainment on the magneto-elastic wave spectrum and on the potential identification of the observed quasi-periodic oscillations (QPOs). We use two-fluid polytropic equations of state to construct our stellar models, which mimic realistic composition gradient configurations. The basic features of the axial axisymmetric spectrum of normal fluid stars are reproduced by our results and in addition we find several magneto-elastic waves with a mixed character. In the core, these oscillations mimic the shear mode pattern of the crust as a result of the strong dynamical coupling between these two regions. Incorporating the most recent entrainment configurations in our models, we find that they have a double effect on the spectrum: the magnetic oscillations of the core have a frequency enhancement, while the mixed magneto-elastic waves originating in the crust are moved towards the frequencies of the single-fluid case. The distribution of lower frequency magneto-elastic oscillations for our models is qualitatively similar to the observed magnetar QPOs with ν In particular, some of these QPOs could represent mixed magneto-elastic oscillations with frequencies not greatly different from the crustal modes of an unmagnetized star. We find that many QPOs could even be accounted for using a model with a relatively weak polar field of Bp ≃ 3 × 1014 G, because of the superfluid enhancement of magnetic oscillations. Finally, we discuss the possible identification of 625 and 1837 Hz QPOs either with non-axisymmetric modes or with high-frequency axisymmetric QPOs excited by crustal mode overtones.
Trapping of superfluid persistent currents in superleaks
International Nuclear Information System (INIS)
Persistent currents in superleaks in contact with bulk superfluid helium have been investigated using Doppler shifts of the acoustic modes of an annular resonator partially packed with superleak and with a simple gyroscopic technique. In an annulus in which the bottom fraction is packed with fine powder and the upper part is left unpacked, there are two hybrid acoustic modes consisting of a combination of the three bulk sounds of superfluid helium, first, second and fourth sound. One mode, with velocity C/sub II/, consists of second sound modified by the presence of the superleak. The other mode, with velocity C14, is an interpolated first and fourth sound mode. The two modes have been studied between the temperatures 1.20K and the lambda temperature for annuli 20, 40, 60 and 80 percent filled with superleak. The velocities obtained were compared with the predictions of the two fluid hydrodynamic theory and good agreement was found. The doppler shifts of C/sub II/ and C14 were used to obtain the persistent current velocities in the unpacked or free section and the packed region of the resonator. It is found that the persistent current velocity in the powder is about the same as is found in a fully packed annulus. The decay of the observed persistent currents was observed for various initial velocities. These observations are discussed in terms of the vortex configurations in the annulus. Vortices form a sheath or cage on the surface of the superleak and prevent loss of angular momentum from the persistent current in the superleak. The arguments are extended to the case of a superleak without walls--a bare superleak--and it is shown that in this case the vortices close on themselves to form a cage to contain the current. Observations were made on a bare superleak by using a simple gyroscopic apparatus suspended from a torsion wire
Self-Ordered Limit Cycles, Chaos, and Phase Slippage with a Superfluid inside an Optical Resonator.
Piazza, Francesco; Ritsch, Helmut
2015-10-16
We study dynamical phases of a driven Bose-Einstein condensate coupled to the light field of a high-Q optical cavity. For high field seeking atoms at red detuning the system is known to show a transition from a spatially homogeneous steady state to a self-ordered regular lattice exhibiting superradiant scattering into the cavity. For blue atom pump detuning the particles are repelled from the maxima of the light-induced optical potential suppressing scattering. We show that this generates a new dynamical instability of the self-ordered phase, leading to the appearance of self-ordered stable limit cycles characterized by large amplitude self-sustained oscillations of both the condensate density and cavity field. The limit cycles evolve into chaotic behavior by period doubling. Large amplitude oscillations of the condensate are accompanied by phase slippage through soliton nucleation at a rate that increases in the chaotic regime. Different from a superfluid in a closed setup, this driven dissipative superfluid is not destroyed by the proliferation of solitons since kinetic energy is removed through cavity losses. PMID:26550874
Enrico Fermi Symposium at CERN : opening celebration
CERN. Geneva. Audiovisual Unit
2002-01-01
You are cordially invited to the opening celebration on Thursday 12 September at 16:00 (Main Building, Council Chamber), which will include speechs from: Luciano Maiani - Welcome and Introduction Antonino Zichichi - The New 'Centro Enrico Fermi' at Via Panisperna Ugo Amaldi - Fermi at Via Panisperna and the birth of Nuclear Medicine Jack Steinberger - Fermi in Chicago Valentin Telegdi - A Close-up of Fermi Arnaldo Stefanini - Celebrating Fermi's Centenary in Documents and Pictures and the screening of a documentary video about Fermi: Scienziati a Pisa: Enrico Fermi (Scientists at Pisa: Enrico Fermi) created by Francesco Andreotti for La Limonaia from early film, photographs and sound recordings (English version - c. 30 mins).
Mott-insulator-to-superfluid transition in the Bose-Hubbard model: A strong-coupling approach
International Nuclear Information System (INIS)
We present a strong-coupling expansion of the Bose-Hubbard model which describes both the superfluid and the Mott phases of ultracold bosonic atoms in an optical lattice. By performing two successive Hubbard-Stratonovich transformations of the intersite hopping term, we derive an effective action which provides a suitable starting point to study the strong-coupling limit of the Bose-Hubbard model. This action can be analyzed by taking into account Gaussian fluctuations about the mean-field approximation as in the Bogoliubov theory of the weakly interacting Bose gas. In the Mott phase, we reproduce results of previous mean-field theories and also calculate the momentum distribution function. In the superfluid phase, we find a gapless spectrum and compare our results with the Bogoliubov theory
Instability of Superfluid Flow in the Neutron Star Core
Link, Bennett
2011-01-01
Pinning of superfluid vortices to magnetic flux tubes in the outer core of a neutron star supports a velocity difference of ~10^5 cm/s between the neutron superfluid and the proton-electron fluid as the star spins down. Under the Magnus force that arises on the vortex array, vortices undergo vortex creep through thermal activation or quantum tunneling. We examine the hydrodynamic stability of this situation. Vortex creep introduces two low-frequency modes, one of which is unstable above a critical wavenumber for any non-zero flow velocity of the neutron superfluid with respect to the charged fluid. For typical pinning parameters of the outer core, the superfluid flow is unstable over wavelengths $\\lambda\\lap 10$ m and over timescales of $\\sim (\\lambda/1 m)^{1/2}$ yr down to $\\sim 1$ d. The vortex lattice could degenerate into a tangle, and the superfluid flow would become turbulent. We suggest that superfluid turbulence could be responsible for the red timing noise seen in many neutron stars, and find a predi...
Acoustic and optical investigations of superfluid 3He. Doctoral thesis
Energy Technology Data Exchange (ETDEWEB)
Manninen, A.
1993-06-15
The thesis is an experimental survey of properties of rotating and stationary superfluid (3)He. Two techniques, acoustics and optics, were used. Ultrasound, together with NMR, has provided most of the present experimental knowledge about the superfluid phases of (3)He. The author applied acoustics for the first time to study rotating (3)He. The main result was the discovery of a new vortex in (3)He-A when the magnetic field is low. New phenomena were observed in stationary (3)He as well. Most importantly, one of the collective modes, the real squashing (rsq) mode, of (3)He-B could be excited by means of two-phonon absorption. Superfluid (3)He was studied optically for the first time. No one has previously seen (3)He in the superfluid state. The principal achievement was developing techniques which facilitate optical experiments at temperatures below 1 mK, required to study superfluid (3)He. Optical fibers were used to transmit light between room temperature and the cold parts of the cryostat. Before these investigations, photography had not been done below 10 mK. The usefulness of optics as a proble of the superfluid phases of (3)He was demonstrated by studying the macroscopic shape of the free surface of rotating (3)He-B. The classical parabolic meniscus was observed, which is indicative of the equilibrium density of vortices.
Josephson effect in fermionic superfluids across the BEC-BCS crossover.
Valtolina, Giacomo; Burchianti, Alessia; Amico, Andrea; Neri, Elettra; Xhani, Klejdja; Seman, Jorge Amin; Trombettoni, Andrea; Smerzi, Augusto; Zaccanti, Matteo; Inguscio, Massimo; Roati, Giacomo
2015-12-18
The Josephson effect is a macroscopic quantum phenomenon that reveals the broken symmetry associated with any superfluid state. Here we report on the observation of the Josephson effect between two fermionic superfluids coupled through a thin tunneling barrier. We show that the relative population and phase are canonically conjugate dynamical variables throughout the crossover from the molecular Bose-Einstein condensate (BEC) to the Bardeen-Cooper-Schrieffer (BCS) superfluid regime. For larger initial excitations from equilibrium, the dynamics of the superfluids become dissipative, which we ascribe to the propagation of vortices through the superfluid bulk. Our results highlight the robust nature of resonant superfluids. PMID:26680193
Schoepe, W.
2015-07-01
This comment is on Phys. Rev. Lett. 144, 155302 (2015) by M.T. Reeves, T.P. Billam, B.P. Anderson, and A.S. Bradley "Identifying a superfluid Reynolds number via dynamical similarity" where a new superfluid Reynolds number is introduced. This definition is shown to be useful in the data analysis of the finite lifetime of turbulence observed with an oscillating sphere in superfluid helium at mK temperatures in a small velocity interval Δ v = ( v-v c ) just above the critical velocity v c . The very rapid increase in the lifetime with increasing superfluid Reynolds number is compared with the "supertransient" turbulence observed in classical pipe flow.
Depletion of the Bose-Einstein condensate in Bose-Fermi mixtures
International Nuclear Information System (INIS)
We describe the properties of a mixture of fermionic and bosonic atoms, as they are tuned across a Feshbach resonance associated with a fermionic molecular state. Provided the number of fermionic atoms exceeds the number of bosonic atoms, we argue that there is a critical detuning at which the Bose-Einstein condensate (BEC) is completely depleted. The phases on either side of this quantum phase transition can also be distinguished by the distinct Luttinger constraints on their Fermi surfaces. In both phases, the total volume enclosed by all Fermi surfaces is constrained by the total number of fermions. However, in the phase without the BEC, which has two Fermi surfaces, there is a second Luttinger constraint: the volume enclosed by one of the Fermi surfaces is constrained by the total number of bosons, so that the volumes enclosed by the two Fermi surfaces are separately conserved. The phase with the BEC may have one or two Fermi surfaces, but only their total volume is conserved. We obtain the phase diagram as a function of atomic parameters and temperature, and describe critical fluctuations in the vicinity of all transitions. We make quantitative predictions valid for the case of a narrow Feshbach resonance, but we expect the qualitative features we describe to be more generally applicable. As an aside, we point out intriguing connections between the BEC depletion transition and the transition to the fractionalized Fermi liquid in Kondo lattice models
Momentum sharing in imbalanced Fermi systems
Hen, O; Weinstein, L B; Piasetzky, E; Hakobyan, H; Higinbotham, D W; Braverman, M; Brooks, W K; Gilad, S; Adhikari, K P; Arrington, J; Asryan, G; Avakian, H; Ball, J; Baltzell, N A; Battaglieri, M; Beck, A; Beck, S May-Tal; Bedlinskiy, I; Bertozzi, W; Biselli, A; Burkert, V D; Cao, T; Carman, D S; Celentano, A; Chandavar, S; Colaneri, L; Cole, P L; Crede, V; DAngelo, A; De Vita, R; Deur, A; Djalali, C; Doughty, D; Dugger, M; Dupre, R; Egiyan, H; Alaoui, A El; Fassi, L El; Elouadrhiri, L; Fedotov, G; Fegan, S; Forest, T; Garillon, B; Garcon, M; Gevorgyan, N; Ghandilyan, Y; Gilfoyle, G P; Girod, F X; Goetz, J T; Gothe, R W; Griffioen, K A; Guidal, M; Guo, L; Hafidi, K; Hanretty, C; Hattawy, M; Hicks, K; Holtrop, M; Hyde, C E; Ilieva, Y; Ireland, D G; Ishkanov, B I; Isupov, E L; Jiang, H; Jo, H S; Joo, K; Keller, D; Khandaker, M; Kim, A; Kim, W; Klein, F J; Koirala, S; Korover, I; Kuhn, S E; Kubarovsky, V; Lenisa, P; Levine, W I; Livingston, K; Lowry, M; Lu, H Y; MacGregor, I J D; Markov, N; Mayer, M; McKinnon, B; Mineeva, T; Mokeev, V; Movsisyan, A; Camacho, C Munoz; Mustapha, B; Nadel-Turonski, P; Niccolai, S; Niculescu, G; Niculescu, I; Osipenko, M; Pappalardo, L L; Paremuzyan, R; Park, K; Pasyuk, E; Phelps, W; Pisano, S; Pogorelko, O; Price, J W; Procureur, S; Prok, Y; Protopopescu, D; Puckett, A J R; Rimal, D; Ripani, M; Ritchie, B G; Rizzo, A; Rosner, G; Rossi, P; Roy, P; Sabatie, F; Schott, D; Schumacher, R A; Sharabian, Y G; Smith, G D; Shneor, R; Sokhan, D; Stepanyan, S S; Stepanyan, S; Stoler, P; Strauch, S; Sytnik, V; Taiuti, M; Tkachenko, S; Ungaro, M; Vlassov, A V; Voutier, E; Watts, D; Walford, N K; Wei, X; Wood, M H; Wood, S A; Zachariou, N; Zana, L; Zhao, Z W; Zheng, X; Zonta, I
2014-01-01
The atomic nucleus is composed of two different kinds of fermions, protons and neutrons. If the protons and neutrons did not interact, the Pauli exclusion principle would force the majority fermions (usually neutrons) to have a higher average momentum. Our high-energy electron scattering measurements using 12C, 27Al, 56Fe and 208Pb targets show that, even in heavy neutron-rich nuclei, short-range interactions between the fermions form correlated high-momentum neutron-proton pairs. Thus, in neutron-rich nuclei, protons have a greater probability than neutrons to have momentum greater than the Fermi momentum. This finding has implications ranging from nuclear few body systems to neutron stars and may also be observable experimentally in two-spin state, ultra-cold atomic gas systems.
Density Functional Theory Studies of Magnetically Confined Fermi Gas
Institute of Scientific and Technical Information of China (English)
陈宇俊; 马红孺
2001-01-01
A theory is developed for magnetically confined Fermi gas at a low temperature based on the density functional theory. The theory is illustrated by the numerical calculation of the density distributions of Fermi atoms 40K with parameters according to DeMarco and Jin's experiment [Science, 285(1999)1703]. Our results are in close agreement with the experiment. To check the theory, we also performed calculations using our theory at a high temperature, which compared very well to the results of the classical limit.
Directory of Open Access Journals (Sweden)
Hao Guo
2015-01-01
Full Text Available Recent experimental progress allows for exploring some important physical quantities of ultracold Fermi gases, such as the compressibility, spin susceptibility, viscosity, optical conductivity, and spin diffusivity. Theoretically, these quantities can be evaluated from suitable linear response theories. For BCS superfluid, it has been found that the gauge invariant linear response theories can be fully consistent with some stringent consistency constraints. When the theory is generalized to stronger than BCS regime, one may meet serious difficulties to satisfy the gauge invariance conditions. In this paper, we try to construct density and spin linear response theories which are formally gauge invariant for a Fermi gas undergoing BCS-Bose-Einstein Condensation (BEC crossover, especially below the superfluid transition temperature Tc. We adapt a particular t-matrix approach which is close to the G0G formalism to incorporate noncondensed pairing in the normal state. We explicitly show that the fundamental constraints imposed by the Ward identities and Q-limit Ward identity are indeed satisfied.
Hartman, Thomas; Strominger, Andrew
2009-01-01
The presence of a massive scalar field near a Kerr black hole is known to produce instabilities associated with bound superradiant modes. In this paper we show that for massive fermions, rather than inducing an instability, the bound superradiant modes condense and form a Fermi sea which extends well outside the ergosphere. The shape of this Fermi sea in phase space and various other properties are analytically computed in the semiclassical WKB approximation. The low energy effective theory near the black hole is described by ripples in the Fermi surface. Expressions are derived for their dispersion relation and the effective force on particles which venture into the sea.
Maccone, C.
In this paper is provided the statistical generalization of the Fermi paradox. The statistics of habitable planets may be based on a set of ten (and possibly more) astrobiological requirements first pointed out by Stephen H. Dole in his book Habitable planets for man (1964). The statistical generalization of the original and by now too simplistic Dole equation is provided by replacing a product of ten positive numbers by the product of ten positive random variables. This is denoted the SEH, an acronym standing for “Statistical Equation for Habitables”. The proof in this paper is based on the Central Limit Theorem (CLT) of Statistics, stating that the sum of any number of independent random variables, each of which may be ARBITRARILY distributed, approaches a Gaussian (i.e. normal) random variable (Lyapunov form of the CLT). It is then shown that: 1. The new random variable NHab, yielding the number of habitables (i.e. habitable planets) in the Galaxy, follows the log- normal distribution. By construction, the mean value of this log-normal distribution is the total number of habitable planets as given by the statistical Dole equation. 2. The ten (or more) astrobiological factors are now positive random variables. The probability distribution of each random variable may be arbitrary. The CLT in the so-called Lyapunov or Lindeberg forms (that both do not assume the factors to be identically distributed) allows for that. In other words, the CLT "translates" into the SEH by allowing an arbitrary probability distribution for each factor. This is both astrobiologically realistic and useful for any further investigations. 3. By applying the SEH it is shown that the (average) distance between any two nearby habitable planets in the Galaxy may be shown to be inversely proportional to the cubic root of NHab. This distance is denoted by new random variable D. The relevant probability density function is derived, which was named the "Maccone distribution" by Paul Davies in
Ultracold Fermi and Bose gases and Spinless Bose Charged Sound Particles
Directory of Open Access Journals (Sweden)
Minasyan V.
2011-10-01
Full Text Available We propose a novel approach for investigation of the motion of Bose or Fermi liquid (or gas which consists of decoupled electrons and ions in the uppermost hyperfine state. Hence, we use such a concept as the fluctuation motion of “charged fluid particles” or “charged fluid points” representing a charged longitudinal elastic wave. In turn, this elastic wave is quantized by spinless longitudinal Bose charged sound particles with the rest mass m and charge e 0 . The existence of spinless Bose charged sound particles allows us to present a new model for description of Bose or Fermi liquid via a non-ideal Bose gas of charged sound particles . In this respect, we introduce a new postulation for the superfluid component of Bose or Fermi liquid determined by means of charged sound particles in the condensate, which may explain the results of experiments connected with ultra-cold Fermi gases of spin-polarized hydrogen, 6 Li and 40 K, and such a Bose gas as 87 Rb in the uppermost hyperfine state, where the Bose- Einstein condensation of charged sound particles is realized by tuning the magnetic field.
Fermionic condensation in ultracold atoms, nuclear matter and neutron stars
Salasnich, Luca
2013-01-01
We investigate the Bose-Einstein condensation of fermionic pairs in three different superfluid systems: ultracold and dilute atomic gases, bulk neutron matter, and neutron stars. In the case of dilute gases made of fermionic atoms the average distance between atoms is much larger than the effective radius of the inter-atomic potential. Here the condensation of fermionic pairs is analyzed as a function of the s-wave scattering length, which can be tuned in experiments by using the technique of...
Medvedev, Mikhail V
2009-01-01
Radiation from GRBs in the prompt phase, flares and an afterglow is thought to be produced by accelerated electrons in magnetic fields. Such emission may be produced at collisionless shocks of baryonic outflows or at reconnection sites (at least for the prompt and flares) of the magnetically dominated (Poynting flux driven) outflows, where no shocks presumably form at all. An astonishing recent discovery is that during reconnection strong small-scale magnetic fields are produced via the Weibel instability, very much like they are produced at relativistic shocks. The relevant physics has been successfully and extensively studied with the PIC simulations in 2D and, to some extent, in 3D for the past few years. We discuss how these simulations predict the existence of MeV-range synchrotron/jitter emission in some GRBs, which can be observed with Fermi. Recent results on modeling of the spectral variability and spectral correlations of the GRB prompt emission in the Weibel-jitter paradigm applicable to both baryo...
Ueresin, C.; Decker, L.; Treite, P.
In 2011, Linde Cryogenics, a division of Linde Process Plants, Tulsa, Oklahoma, was awarded the contract to deliver a 500 W at 2 K superfluid cryogenic plant to Fermi National Accelerator Laboratory (FNAL) in Batavia, Illinois, USA. This system includes a cold compressor string with three centrifugal compressors and a vacuum pump skid with five volumetric pumps in parallel used to pump down helium to its saturation pressure corresponding to 2 K. Linde Kryotechnik AG, Pfungen Switzerland engineered and supplied the cold compressor system and commissioned it with its control logic to cover the complete range of system operation. The paper outlines issues regarding compressor design, compressor string modeling, control algorithms, controller performance, and surge protection.
Energy-momentum tensor of quasiparticles in the effective gravity in superfluids
Volovik, G.E.
1998-01-01
The problem of the energy-momentum conservation for matter in the gravitational field is discussed on the example of the effective gravity, which arises in superfluids. The "gravitational" field experienced by the relativistic-like massless quasiparticles which form the "matter" (phonons in superfluid 4He and low-energy fermions in superfluid 3He-A), is induced by the flow of the superfluid "vacuum". It appears that the energy-momentum conservation law for quasiparticles, has the covariant fo...
Renormalization group approach to superfluid neutron matter
International Nuclear Information System (INIS)
In the present thesis superfluid many-fermion systems are investigated in the framework of the Renormalization Group (RG). Starting from an experimentally determined two-body interaction this scheme provides a microscopic approach to strongly correlated many-body systems at low temperatures. The fundamental objects under investigation are the two-point and the four-point vertex functions. We show that explicit results for simple separable interactions on BCS-level can be reproduced in the RG framework to high accuracy. Furthermore the RG approach can immediately be applied to general realistic interaction models. In particular, we show how the complexity of the many-body problem can be reduced systematically by combining different RG schemes. Apart from technical convenience the RG framework has conceptual advantage that correlations beyond the BCS level can be incorporated in the flow equations in a systematic way. In this case however the flow equations are no more explicit equations like at BCS level but instead a coupled set of implicit equations. We show on the basis of explicit calculations for the single-channel case the efficacy of an iterative approach to this system. The generalization of this strategy provides a promising strategy for a non-perturbative treatment of the coupled channel problem. By the coupling of the flow equations of the two-point and four-point vertex self-consistency on the one-body level is guaranteed at every cutoff scale. (orig.)
Superfluid Turbulence in a Nonuniform Circular Channel
Murphy, Paul Joseph
The excess dissipation due to the presence of quantized vorticity in flowing helium has been studied extensively. The success of the microscopic theory proposed by Schwarz in describing many properties of this dissipation led to a belief that the major aspects of the problem had been understood at the microscopic level. The experiment of Kafkalidis and Tough demonstrated that a weak one dimensional nonuniformity in the flow field led to a dramatic departure between the observed behavior and the predictions of the Schwarz theory using the local uniformity approximation (LUA). The research presented in this thesis was undertaken to measure the dissipative states for thermal counterflow with a weak two dimensional nonuniformity. The experiment of Kafkalidis and Tough used a flow channel with a high aspect ratio. Such channels are known to exhibit only one state of superfluid turbulence. In this research the channel is circular in cross section and shows two distinct turbulent states (T-I and T-II). This experiment demonstrates that there is no difference in the excess dissipation for flows that are either converging or diverging. The T-I state is described by the same parameters as the T-I state in uniform channels. The turbulence exhibits front behavior at the transition between states. These conclusions are consistent with the LUA. The T-II state is at variance with the LUA, but is consistant with the results found in the Kafkalidis and Tough experiment.
Superfluid turbulence in a nonuniform circular channel
International Nuclear Information System (INIS)
The excess dissipation due to the presence of quantized vorticity in flowing helium has been studied extensively. The success of the microscopic theory proposed by Schwarz in describing many properties of this dissipation led to a belief that the major aspects of the problem had been understood at the microscopic level. The experiment of Kafkalidis and Tough demonstrated that a weak one dimensional nonuniformity in the flow field led to a dramatic departure between the observed behavior and the predictions of the Schwarz theory using the local uniformity approximation (LUA). The research presented in this thesis was undertaken to measure the dissipative states for thermal counterflow with a weak two dimensional nonuniformity. The experiment of Kafkalidis and Tough used a flow channel with a high aspect ratio. Such channels are known to exhibit only one state of superfluid turbulence. In this research the channel is circular in cross section and shows two distinct turbulent states (T-I and T-II). This experiment demonstrates that there is no difference in the excess dissipation for flows that are either converging or diverging. The T-I state is described by the same parameters as the T-I state in uniform channels. The turbulence exhibits front behavior at the transition between states. These conclusions are consistent with the LUA. The T-II state is at variance with the LUA, but is consistent with the results found in the Kafkalidis and Tough experiment
Microscopic characterization of overpressurized superfluid 4He
Rossi, M.; Vitali, E.; Reatto, L.; Galli, D. E.
2012-01-01
We have studied static and dynamical properties of superfluid 4He at T=0 K in the pressure range from -6 up to 87 atm well above freezing into the metastable region. Zero temperature properties have been obtained with the exact shadow path integral ground state (SPIGS) method. Information about dynamic structure factors at different pressures have been obtained from imaginary time correlation functions via the genetic inversion via falsification of theories (GIFT) method. In the full pressure range sharp roton excitations are always present in the spectral functions. The roton energy decreases at higher pressures in good agreement with experimental data also in the metastable region. The roton energies have essentially a linear trend with pressure, going from about 7.4 K near freezing to about 4.3 K at about 87 atm. The pressure at which the linear trend would extrapolate to a zero roton energy turns out to be about 170 atm. At T=0 K, no sign of metastable glass phase has been found; the disordered systems studied at pressures above about 87 atm readily start homogeneous nucleation processes. Our results in the metastable phase for the condensate fractions and roton gaps differ remarkably from previous ones obtained via a diffusion Monte Carlo study.
Buoyancy and g-modes in young superfluid neutron stars
Passamonti, A.; Andersson, N.; Ho, W. C. G.
2016-01-01
We consider the local dynamics of a realistic neutron-star core, including composition gradients, superfluidity and thermal effects. The main focus is on the gravity g-modes, which are supported by composition stratification and thermal gradients. We derive the equations that govern this problem in full detail, paying particular attention to the input that needs to be provided through the equation of state and distinguishing between normal and superfluid regions. The analysis highlights a number of key issues that should be kept in mind whenever equation of state data is compiled from nuclear physics for use in neutron-star calculations. We provide explicit results for a particular stellar model and a specific nucleonic equation of state, making use of cooling simulations to show how the local wave spectrum evolves as the star ages. Our results show that the composition gradient is effectively dominated by the muons whenever they are present. When the star cools below the superfluid transition, the support for g-modes at lower densities (where there are no muons) is entirely thermal. We confirm the recent suggestion that the g-modes in this region may be unstable, but our results indicate that this instability will be weak and would only be present for a brief period of the star's life. Our analysis accounts for the presence of thermal excitations encoded in entrainment between the entropy and the superfluid component. Finally, we discuss the complete spectrum, including the normal sound waves and, in superfluid regions, the second sound.
Quantum chromodynamics as a microscopic theory of superfluidity
International Nuclear Information System (INIS)
It is shown that the hypothesis of the singular Bose-condensate and collective excitation can be realized in the Yang-Mills quantum theory at a definite choice of the dynamical variables. This idea is developed by using the analogy with the microscopic theory of superfluidity. The spectrum of quasiparticle excitations is obtained for the Bose-condensate in the class of cylindrically symmetric functions. It is shown that nonobservability of coloured quasiparticles can be a result of superfluid properties of vortices of the Bose-condensate. The comparison with superfluid helium in a rotating bucket has shown that it may happen to be impossible theoretically, without experimental facts, to define the parameters of gluon ''vortices'', i.e., the dimension and spatial configuration of gluon bags
Mott-superfluid transition of q-deformed bosons
International Nuclear Information System (INIS)
The effect of q-deformation of the bosonic algebra on the Mott-superfluid transition for interacting lattice bosons described by the Bose–Hubbard model is studied using mean-filed theory. It has been shown that the Mott state proliferates and the initial periodicity of the Mott lobes as a function of the chemical potential disappears as the q-deformation increases. The ground state phase diagram as a function of the q-parameter exhibits superfluid order, which intervenes in narrow regions between Mott lobes, demonstrating the new concept of statistically induced quantum phase transition. - Highlights: • We study the effect of q-deformed bosons on superfluid transition. • A mean-field theory is employed. • Bosons can change statistics due to deformation of the commutation rules. • Statistically induced quantum phase transition is found
Inhomogeneous structures in holographic superfluids. I. Dark solitons
International Nuclear Information System (INIS)
We begin an investigation of inhomogeneous structures in holographic superfluids. As a first example, we study domain wall-like defects in the 3+1 dimensional Einstein-Maxwell-Higgs theory, which was developed as a dual model for a holographic superconductor. In [V. Keraenen, E. Keski-Vakkuri, S. Nowling, and K. P. Yogendran, Phys. Rev. D 80, 121901 (2009).], we reported on such ''dark solitons'' in holographic superfluids. In this work, we present an extensive numerical study of their properties, working in the probe limit. We construct dark solitons for two possible condensing operators and find that both of them share common features with their standard superfluid counterparts. However, both are characterized by two distinct coherence length scales (one for order parameter, one for charge condensate). We study the relative charge depletion factor and find that solitons in the two different condensates have very distinct depletion characteristics.
Buoyancy and g-modes in young superfluid neutron stars
Passamonti, A; Ho, W C G
2015-01-01
We consider the local dynamics of a realistic neutron star core, including composition gradients, superfluidity and thermal effects. The main focus is on the gravity g-modes, which are supported by composition stratification and thermal gradients. We derive the equations that govern this problem in full detail, paying particular attention to the input that needs to be provided through the equation of state and distinguishing between normal and superfluid regions. The analysis highlights a number of key issues that should be kept in mind whenever equation of state data is compiled from nuclear physics for use in neutron star calculations. We provide explicit results for a particular stellar model and a specific nucleonic equation of state, making use of cooling simulations to show how the local wave spectrum evolves as the star ages. Our results show that the composition gradient is effectively dominated by the muons whenever they are present. When the star cools below the superfluid transition, the support fo...
On the disappearance of superfluidity in helium films
International Nuclear Information System (INIS)
Experiments to investigate the changes in superfluid properties when helium films become thinner are reported. A thin-film oscillator, formed by two large filmreservoirs connected by a long and narrow tube, is used to study both the mass transport properties and the third-sound phenomena. Both sets of data are analysed in the framework of a two-fluid model. Absolute values for the areal superfluid density are deduced from the results, and also the observation of friction in the film itself is briefly discussed. A series of additional measurements of the thermo-mechanical effect in the reservoirs, with the purpose of determing the thickness at which onset of superfluidity occurs, are also reported. Finally the overall picture of the film properties is discussed on the basis of a phase diagram of the observed mobilities. (Auth.)
Josephson flow oscillations in superfluid 3He-B
International Nuclear Information System (INIS)
Experiments for observing pressure-induced Josephson oscillations in superfluid 4He renewed the interest for analogous experiments in superfluid 3He. The weak coupling of two superfluids is obtained by a small channel with dimensions in the order of the coherence length. The order-parameter functions, the supercurrent Jψ through the orifice, and the Ginzburg-Landau free energy, Fψ is calculated for different cross sections. A new feature of the function Jψ in comparison to the current-phase relationships for superconducting microbridges is the occurrence of two nontrivial zeros of Jψ. It turns out that the frequency, ω, of the Josephson flow oscillations, which follow the sudden application of a force ΔF on a diaphragm, depends on ΔF in a way similar to that in which the frequency of the parallel ringing experiment in 3He-Α depends on the field step ΔΗ. (6 refs., 12 figs.)
From field theory to superfluid hydrodynamics of dense quark matter
Alford, Mark G; Schmitt, Andreas; Stetina, Stephan
2013-01-01
Hydrodynamics of superfluids can be described by formally dividing the fluid into a normal fluid and a superfluid part. In color-flavor locked quark matter, at least one superfluid component is present due to spontaneous breaking of baryon number conservation, and an additional one due to the breaking of strangeness arises once one takes into account kaon condensation. We show how such a two-component description emerges from an underlying scalar field theory which can be viewed as an effective theory for kaons. Furthermore, the occurring hydrodynamic quantities in the low-temperature limit are related to the microscopic parameters provided by the Lagrangian which closes the gap between field theory and hydrodynamics, which are important for astrophysical calculations.
A minimal model for finite temperature superfluid dynamics
Andersson, N; Comer, G L; Samuelsson, L
2012-01-01
Building on a recently improved understanding of the problem of heat flow in general relativity, we develop a hydrodynamical model for coupled finite temperature superfluids. The formalism is designed with the dynamics of the outer core of a mature neutron star (where superfluid neutrons are coupled to a conglomerate of protons and electrons) in mind, but the main ingredients are relevant for a range of analogous problems. The entrainment between material fluid components (the condensates) and the entropy (the thermal excitations) plays a central role in the development. We compare and contrast the new model to previous results in the literature, and provide estimates for the relevant entrainment coefficients that should prove useful in future applications. Finally, we consider the sound-wave propagation in the system in two simple limits, demonstrating the presence of second sound if the temperature is sub-critical, but absence of this phenomenon above the critical temperature for superfluidity.
Mott-superfluid transition of q-deformed bosons
Energy Technology Data Exchange (ETDEWEB)
Kopeć, T.K., E-mail: kopec@int.pan.wroc.pl
2015-10-16
The effect of q-deformation of the bosonic algebra on the Mott-superfluid transition for interacting lattice bosons described by the Bose–Hubbard model is studied using mean-filed theory. It has been shown that the Mott state proliferates and the initial periodicity of the Mott lobes as a function of the chemical potential disappears as the q-deformation increases. The ground state phase diagram as a function of the q-parameter exhibits superfluid order, which intervenes in narrow regions between Mott lobes, demonstrating the new concept of statistically induced quantum phase transition. - Highlights: • We study the effect of q-deformed bosons on superfluid transition. • A mean-field theory is employed. • Bosons can change statistics due to deformation of the commutation rules. • Statistically induced quantum phase transition is found.
Pulsed NMR experiments in superfluid 3He confined in aerogel
International Nuclear Information System (INIS)
Pulsed NMR experiments have been performed in both B and supercooled A phases of superfluid 3He in aerogel. Dependencies of spin precession frequency on tipping angle in B-phase of superfluid 3He in aerogel are found to be different for pure 3He and for the cell preplated with 4He. A sharp increase of the frequency for tipping angles greater than 104 deg. was observed in low temperature superfluid phase of 3He in 4He preplated aerogel as it is expected for the B-phase structure of the order parameter. Dependencies of the frequency on the tipping angle in supercooled A-phase are similar for both pure 3He and 4He preplated aerogel
A minimal model for finite temperature superfluid dynamics
Andersson, N.; Krüger, C.; Comer, G. L.; Samuelsson, L.
2013-12-01
Building on a recently improved understanding of the problem of heat flow in general relativity, we develop a hydrodynamical model for coupled finite temperature superfluids. The formalism is designed with the dynamics of the outer core of a mature neutron star (where superfluid neutrons are coupled to a conglomerate of protons and electrons) in mind, but the main ingredients are relevant for a range of analogous problems. The entrainment between material fluid components (the condensates) and the entropy (the thermal excitations) plays a central role in the development. We compare and contrast the new model to previous results in the literature, and provide estimates for the relevant entrainment coefficients that should prove useful in future applications. Finally, we consider the sound-wave propagation in the system in two simple limits, demonstrating the presence of second sound if the temperature is sub-critical, but absence of this phenomenon above the critical temperature for superfluidity.
Bose-Fermi mixtures near an interspecies Feshbach resonance: testing a non-equilibrium approach
Energy Technology Data Exchange (ETDEWEB)
Bortolotti, Daniele C E [JILA and Department of Physics, University of Colorado Boulder, CO 80309-0440 (United States); LENS and Dipartimento di Fisica, Universita di Firenze, and INFM, Sesto Fiorentino (Italy); Avdeenkov, Alexandr V [Institute of Physics and Power Engineering, Obninsk (Russian Federation); Ticknor, Christopher [JILA and Department of Physics, University of Colorado Boulder, CO 80309-0440 (United States); Bohn, John L [JILA and Department of Physics, University of Colorado Boulder, CO 80309-0440 (United States)
2006-01-14
We test a non-equilibrium approach to study the behaviour of a Bose-Fermi mixture of alkali atoms in the presence of a Feshbach resonance between bosons and fermions. To this end we derive the Hartree-Fock-Bogoliubov (HFB) equations of motion for the interacting system. This approach has proven very successful in the study of resonant systems composed of Bose particles and Fermi particles. However, when applied to a Bose-Fermi mixture, the HFB theory fails to identify even the correct binding energy of molecules in the appropriate limit. Through a more rigorous analysis we are able to ascribe this difference to the peculiar role that noncondensed bosons play in the Bose-Fermi pair correlation, which is the mechanism through which molecules are formed. We therefore conclude that molecular formation in Bose-Fermi mixtures is driven by three-point and higher-order correlations in the gas.
Bose-Fermi mixtures near an interspecies Feshbach resonance: testing a non-equilibrium approach
International Nuclear Information System (INIS)
We test a non-equilibrium approach to study the behaviour of a Bose-Fermi mixture of alkali atoms in the presence of a Feshbach resonance between bosons and fermions. To this end we derive the Hartree-Fock-Bogoliubov (HFB) equations of motion for the interacting system. This approach has proven very successful in the study of resonant systems composed of Bose particles and Fermi particles. However, when applied to a Bose-Fermi mixture, the HFB theory fails to identify even the correct binding energy of molecules in the appropriate limit. Through a more rigorous analysis we are able to ascribe this difference to the peculiar role that noncondensed bosons play in the Bose-Fermi pair correlation, which is the mechanism through which molecules are formed. We therefore conclude that molecular formation in Bose-Fermi mixtures is driven by three-point and higher-order correlations in the gas
Parity effect in a mesoscopic Fermi gas
Hofmann, Johannes; Lobos, Alejandro M.; Galitski, Victor
2016-06-01
We develop a quantitative analytic theory that accurately describes the odd-even effect observed experimentally in a one-dimensional, trapped Fermi gas with a small number of particles [G. Zürn et al., Phys. Rev. Lett. 111, 175302 (2013), 10.1103/PhysRevLett.111.175302]. We find that the underlying physics is similar to the parity effect known to exist in ultrasmall mesoscopic superconducting grains and atomic nuclei. However, in contrast to superconducting nanograins, the density (Hartree) correction dominates over the superconducting pairing fluctuations and leads to a much more pronounced odd-even effect in the mesoscopic, trapped Fermi gas. We calculate the corresponding parity parameter and separation energy using both perturbation theory and a path integral framework in the mesoscopic limit, generalized to account for the effects of the trap, pairing fluctuations, and Hartree corrections. Our results are in an excellent quantitative agreement with experimental data and exact diagonalization. Finally, we discuss a few-particle to many-particle crossover between the perturbative mesoscopic regime and nonperturbative many-body physics that the system approaches in the thermodynamic limit.
Superfluid Heat Conduction and the Cooling of Magnetized Neutron Stars
Aguilera, Deborah N.; Cirigliano, Vincenzo; Pons, José A.; Reddy, Sanjay; Sharma, Rishi
2008-01-01
We report on a new mechanism for heat conduction in the neutron star crust. We find that collective modes of superfluid neutron matter, called superfluid phonons (sPhs), can influence heat conduction in magnetized neutron stars. They can dominate the heat conduction transverse to magnetic field when the magnetic field $B \\gsim 10^{13}$ G. At density $\\rho \\simeq 10^{12}-10^{14} $ g/cm$^3$ the conductivity due to sPhs is significantly larger than that due to lattice phonons and is comparable t...
Quantised vortices and mutual friction in relativistic superfluids
Andersson, N; Vickers, J A
2016-01-01
We consider the detailed dynamics of an array of quantised superfluid vortices in the framework of general relativity, as required for quantitative modelling of realistic neutron star cores. Our model builds on the variational approach to relativistic (multi-) fluid dynamics, where the vorticity plays a central role. The description provides a natural extension of, and as it happens a better insight into, existing Newtonian models. In particular, we account for the mutual friction associated with scattering of a second "normal" component in the mixture off of the superfluid vortices.
The Fermi Paradox is Neither Fermis Nor a Paradox
Gray, Robert H.
2016-01-01
The so-called Fermi paradox claims that if technological life existed anywhere else, we would see evidence of its visits to Earth-and since we do not, such life does not exist, or some special explanation is needed. Enrico Fermi, however, never published anything on this topic. On the one occasion he is known to have mentioned it, he asked 'where is everybody?'- apparently suggesting that we don't see extraterrestrials on Earth because interstellar travel may not be feasible, but not suggesti...
Conjugate Fermi holes and its manifestation in He-like systems
International Nuclear Information System (INIS)
The structure of genuine and conjugate Fermi holes in two-electron atomic systems, namely He and He-like atomic ions, has been studied relying on accurate full configuration interaction wave functions. The standard Fermi hole exists in the vicinity of region in the two-electron coordinate space satisfying the well-known condition, r1 = r2, while the conjugate Fermi hole exists in the vicinity of region close to this genuine Fermi hole but satisfying r1 ≠ r2 instead of r1 = r2. Existence of these holes has shown to give an insightful interpretation of the origin of the first Hund rule and of the anomalously strong angular correlation manifested in the series of the singlet-triplet pair of singly-excited states of the aforementioned systems
Cinema, Fermi Problems, & General Education
Efthimiou, C J
2006-01-01
During the past several years the authors have developed a new approach to the teaching of Physical Science, a general education course typically found in the curricula of nearly every college and university. This approach, called `Physics in Films', uses scenes from popular movies to illustrate physical principles and has excited student interest and improved student performance. The analyses of many of the scenes in `Physics in Films' are a direct application of Fermi calculations -- estimates and approximations designed to make solutions of complex and seemingly intractable problems understandable to the student non-specialist. The intent of this paper is to provide instructors with examples they can use to develop skill in recognizing Fermi problems and making Fermi calculations in their own courses.
Charge distribution and Fermi level in bimetallic nanoparticles
Holmberg, Nico; Laasonen, Kari; Peljo, Pekka Eero
2016-01-01
Upon metal-metal contact, a transfer of electrons will occur between the metals until the Fermi levels in both phases are equal, resulting in a net charge difference across the metal-metal interface. Here, we have examined this contact electrification in bimetallic model systems composed of mixed Au-Ag nanoparticles containing ca. 600 atoms using density functional theory calculations. We present a new model to explain this charge transfer by considering the bimetallic system as a nanocapacit...
Information entropy and Thomas-Fermi screening functions
International Nuclear Information System (INIS)
In this work we apply the information entropy concept to analyze different trial electron densities in momentum and coordinate spaces, into the Thomas-Fermi density functional formalism. Furthermore, we try to assess how well-known physical properties of neutral atoms are reproduced and hence evaluate the quality of the screening functions in the light of their predictive capacity. (author). 32 refs, 4 figs, 3 tabs
Relativistic Thomas-Fermi Model at Finite Temperatures
G. Bertone(GRAPPA Center of Excellence, University of Amsterdam, Science Park 904, 1090 GL Amsterdam, The Netherlands); Ruffini, R.
2001-01-01
We briefly review the Thomas-Fermi statistical model of atoms in the classical non-relativistic formulation and in the generalised finite-nucleus relativistic formulation. We then discuss the classical generalisation of the model to finite temperatures in the non-relativistic approximation and present a new relativistic model at finite temperatures, investigating how to recover the existing theory in the limit of low temperatures. This work is intended to be a propedeutical study for the eval...
Ho, Wynn C G; Espinoza, Cristobal M; Glampedakis, Kostas; Haskell, Brynmor; Heinke, Craig O
2013-01-01
We present recent work on using astronomical observations of neutron stars to reveal unique insights into nuclear matter that cannot be obtained from laboratories on Earth. First, we discuss our measurement of the rapid cooling of the youngest neutron star in the Galaxy; this provides the first direct evidence for superfluidity and superconductivity in the supra-nuclear core of neutron stars. We show that observations of thermonuclear X-ray bursts on neutron stars can be used to constrain properties of neutron superfluidity and neutrino emission. We describe the implications of rapid neutron star rotation rates on aspects of nuclear and superfluid physics. Finally, we show that entrainment coupling between the neutron superfluid and the nuclear lattice leads to a less mobile crust superfluid; this result puts into question the conventional picture of pulsar glitches as being solely due to the crust superfluid and suggests that the core superfluid also participates.
DEFF Research Database (Denmark)
Bruun, Georg
2011-01-01
We examine spin diffusion in a two-component homogeneous Fermi gas in the normal phase. Using a variational approach, analytical results are presented for the spin diffusion coefficient and the related spin relaxation time as a function of temperature and interaction strength. For low temperatures......, strong correlation effects are included through the Landau parameters which we extract from Monte Carlo results. We show that the spin diffusion coefficient has a minimum for a temperature somewhat below the Fermi temperature with a value that approaches the quantum limit ~/m in the unitarity regime...
Quantum supersymmetric Fermi-solitons
International Nuclear Information System (INIS)
We investigate the quantum field theory, which is given on Minkowski manifold Md with its number of dimensions d>4 and is invariant under the group of nonlinear supersymmetric transformations proposed by Volkov and Akulov. It is shown that the vacuum state of this field theory, after such a compactification of the additional dimensions as Md → M4 centre dot Vd-4, is a particle-like Fermi-soliton. Its characteristic radius coincides with that of the compactified manifold Vd-4, and such an object is defined as a quantum supersymmetric Fermi-soliton
Palade, D I
2014-01-01
We study the static linear response in spherical Thomas-Fermi systems deriving a simple diferen- tial equation for general multipolar moments and associated polarizabilities. We test the equation on sodium clusters between 20 and 100 atoms and on fullerenes between C60 and C240 and propose it for general Thomas-Fermi systems. Our simple method provides results which deviates from experimental data with less then 15%.
BEC of 41 K in a Fermi sea of 6 Li
Lous, Rianne S.; Fritsche, Isabella; Huang, Bo; Jag, Michael; Cetina, Marko; Walraven, Jook T. M.; Grimm, Rudolf
2016-05-01
We report on the production of a 41 K Bose-Einstein condensate (BEC) immersed in a degenerate two-component 6 Li Fermi sea. After evaporation in an optical dipole trap, we obtain 1 . 2 ×104 41 K atoms with a 55% BEC fraction and a Fermi sea with T /TF work is supported by the Austrian Science Fund FWF within the collaborative research grant FoQuS.
The Low Density Matter (LDM) beamline at FERMI: optical layout and first commissioning
Energy Technology Data Exchange (ETDEWEB)
Svetina, Cristian [Elettra-Sincrotrone Trieste, I-34149 Trieste (Italy); Graduate School of Nanotechnology, University of Trieste, I-34127 Trieste (Italy); Grazioli, Cesare, E-mail: cesare.grazioli@elettra.eu [Department of Chemical and Pharmaceutical Sciences, University of Trieste, 34127 Trieste (Italy); CNR-IOM TASC, Area Science Park Basovizza, I-34149 Trieste (Italy); Laboratory of Quantum Optics, University of Nova Gorica, Nova Gorica (Slovenia); Mahne, Nicola; Raimondi, Lorenzo; Fava, Claudio [Elettra-Sincrotrone Trieste, I-34149 Trieste (Italy); and others
2015-04-21
A description of the LDM beamline of FERMI is given, with a detailed description of the photon transport. The Low Density Matter (LDM) beamline has been built as part of the FERMI free-electron laser (FEL) facility to serve the atomic, molecular and cluster physics community. After the commissioning phase, it received the first external users at the end of 2012. The design and characterization of the LDM photon transport system is described, detailing the optical components of the beamline.
The Fermi Paradox is Neither Fermis Nor a Paradox
Gray, Robert H
2016-01-01
The so-called Fermi paradox claims that if technological life existed anywhere else, we would see evidence of its visits to Earth-and since we do not, such life does not exist, or some special explanation is needed. Enrico Fermi, however, never published anything on this topic. On the one occasion he is known to have mentioned it, he asked 'where is everybody?'- apparently suggesting that we don't see extraterrestrials on Earth because interstellar travel may not be feasible, but not suggesting that intelligent extraterrestrial life does not exist, or suggesting its absence is paradoxical. The claim 'they are not here; therefore they do not exist' was first published by Michael Hart, claiming that interstellar travel and colonization of the galaxy would be inevitable if intelligent extraterrestrial life existed, and taking its absence here as proof that it does not exist anywhere. The Fermi paradox appears to originate in Hart's argument, not Fermi's question. Clarifying the origin of these ideas is important...
Third sound measurements of superfluid 4He films on multiwall carbon nanotubes below 1 K
International Nuclear Information System (INIS)
Third sound is studied for superfluid films of 4He adsorbed on multiwall carbon nanotubes packed into an annular resonator. The third sound is generated with mechanical oscillation of the cell, and detected with carbon bolometers. A filling curve at temperatures near 250 mK shows oscillations in the third sound velocity, with maxima at the completion of the 4th and 5th atomic layers. Sharp changes in the Q factor of the third sound are found at partial layer fillings. Temperature sweeps at a number of fill points show strong broadening effects on the Kosterlitz-Thouless (KT) transition, and rapidly increasing dissipation, in qualitative agreement with the predictions of Machta and Guyer. At the 4th layer completion there is a sudden reduction of the transition temperature TKT, and then a recovery back to linear variation with temperature, although the slope is considerably smaller than the KT prediction
Engineering mesoscopic superpositions of superfluid flow
Hallwood, David W
2011-01-01
Modeling strongly correlated atoms demonstrates the possibility to prepare quantum superpositions that are robust against experimental imperfections and temperature. Such superpositions of vortex states are formed by adiabatic manipulation of interacting ultracold atoms confined to a one-dimensional ring trapping potential when stirred by a barrier. Here, we discuss the influence of non-ideal experimental procedures and finite temperature. Adiabaticity conditions for changing the stirring rate reveal that superpositions of many atoms are most easily accessed in the strongly-interacting, Tonks-Girardeau, regime, which is also the most robust at finite temperature. NOON-type superpositions of weakly interacting atoms are most easily created by adiabatically decreasing the interaction strength by means of a Feshbach resonance. The quantum dynamics of small numbers of particles is simulated and the size of the superpositions is calculated based on their ability to make precision measurements. Experimental creatio...
Electron Attachment to CO2 Embedded in Superfluid He Droplets
Postler, Johannes; Vizcaino, Violaine; Denifl, Stephan; Zappa, Fabio; Ralser, Stefan; Daxner, Matthias; Illenberger, Eugen; Scheier, Paul
2014-01-01
Electron attachment to CO2 embedded in superfluid He droplets leads to ionic complexes of the form (CO2) n – and (CO2) n O– and, at much lower intensities, He containing ions of the form He m (CO2) n O–. At low energies (
Briton wins Nobel physics prize for work on superfluids
Connor, S
2003-01-01
A British born scientist, Anthony Leggett, 65, has jointly won this year's Nobel prize in physics for research into the arcane area of superfluids - when matter behaves in its lowest and most ordered state. He shares the 800,000 pounds prize with two Russian physicists who have worked in the field of superconductivity - when electrical conductors lose resistance (1/2 page).
H on He: sticking and 2d-superfluidity
International Nuclear Information System (INIS)
The sticking coefficient, which governs the sticking time τs, is discussed for high surface-coverage conditions. We point out that τs must remain large compared to a characteristic vortex diffusion time, if the system is to display 2d-superfluidity
The phenomenon of superfluidity in an electron system of crystals
International Nuclear Information System (INIS)
Experimental data are obtained as for the possibility of the luminescent indication of new properties of molecular electron-hole liquid β-Zn P2 crystals. The structure of their spectrum is explained with the dispersion law for quantum liquid elementary states typical of superfluidity states
Dislocation-induced superfluidity in a model supersolid
Energy Technology Data Exchange (ETDEWEB)
Goswami, Debajit [Universitaet des Saarlandes, Saarbruecken (Germany); Dasbiswas, Kinjal; Dorsey, Alan [University of Florida, Gainesville, FL (United States); Yoo, Chi-Deuk [University of Minnesota, Minneapolis, MN (United States)
2012-07-01
Motivated by recent experiments on the supersolid behavior of {sup 4}He, we study the effect of an edge dislocation in promoting superfluidity in a Bose crystal. Using Landau theory, we couple the elastic strain field of the dislocation to the superfluid density, and use a linear analysis to show that superfluidity nucleates on the dislocation before occurring in the bulk of the solid. Moving beyond the linear analysis, we develop a systematic perturbation theory in the weakly nonlinear regime, and use this method to integrate out transverse degrees of freedom and derive a one-dimensional Landau equation for the superfluid order parameter. We then extend our analysis to a network of dislocation lines, and derive an XY model for the dislocation network by integrating over fluctuations in the order parameter. Our results show that the ordering temperature for the network has a sensitive dependence on the dislocation density, consistent with numerous experiments that find a clear connection between the sample quality and the supersolid response.
Design and testing of a superfluid liquid helium cooling loop
International Nuclear Information System (INIS)
This paper describes the design and preliminary testing of a cryogenic cooling loop that uses a thermomechanical pump to circulate superfluid liquid helium. The cooling loop test apparatus is designed to prove forced liquid helium flow concepts that will be used on the Astromag superconducting magnet facility. 3 refs., 2 figs
Three Types of Cooling Superfluid Neutron Stars Theory and Observations
Kaminker, A D; Gnedin, O Y
2002-01-01
Cooling of neutron stars (NSs) with the cores composed of neutrons, protons, and electrons is simulated assuming $^1$S$_0$ pairing of neutrons in the NS crust, and also $^1$S$_0$ pairing of protons and weak $^3$P$_2$ pairing of neutrons in the NS core, and using realistic density profiles of the superfluid critical temperatures $T_{\\rm c}(\\rho)$. The theoretical cooling models of isolated middle-aged NSs can be divided into three main types. (I) {\\it Low-mass}, {\\it slowly cooling} NSs where the direct Urca process of neutrino emission is either forbidden or almost fully suppressed by the proton superfluidity. (II) {\\it Medium-mass} NSs which show {\\it moderate} cooling via the direct Urca process suppressed by the proton superfluidity. (III) {\\it Massive} NSs which show {\\it fast} cooling via the direct Urca process weakly suppressed by superfluidity. Confronting the theory with observations we treat RX J0822--43, PSR 1055--52 and RX J1856--3754 as slowly cooling NSs. To explain these sufficiently warm sourc...
How viscous is a superfluid neutron star core?
Andersson, N; Glampedakis, K
2004-01-01
In this paper we discuss the effects of superfluidity on the shear viscosity in a neutron star core. Our study combines existing theoretical results for the viscosity coefficients with data for the various superfluid energy gaps into a consistent description. In particular, we provide a simple model for the electron viscosity which is relevant both when the protons form a normal fluid and when they become superconducting. This result explains in a clear way why proton superconductivity leads to a significant strengthening of the shear viscosity. We present our results in a form which permits the use of data for any given modern equation of state (our final formulas are explicitly dependent on the proton fraction). We discuss a simple description of the relevant superfluid pairing gaps, and construct a number of models (spanning the range of current uncertainty) which are then used to discuss the superfluid suppression of shear viscosity. We conclude by a discussion of a number of challenges that must be met i...
Order-disorder oscillations in exciton-polariton superfluids.
Saito, Hiroki; Aioi, Tomohiko; Kadokura, Tsuyoshi
2013-01-11
The dynamics of an exciton-polariton superfluid resonantly pumped in a semiconductor microcavity are investigated by mean-field theory. Modulational instability develops into crystalline order, and then, ordered and disordered states alternately form. It is found that the crystalline order at rest can coexist with superflow. PMID:23383923
Laser cooling and control of excitations in superfluid helium
Harris, G. I.; McAuslan, D. L.; Sheridan, E.; Sachkou, Y.; Baker, C.; Bowen, W. P.
2016-08-01
Superfluidity is a quantum state of matter that exists macroscopically in helium at low temperatures. The elementary excitations in superfluid helium have been probed with great success using techniques such as neutron and light scattering. However, measurements of phonon excitations have so far been limited to average thermodynamic properties or the driven response far out of thermal equilibrium. Here, we use cavity optomechanics to probe the thermodynamics of phonon excitations in real time. Furthermore, strong light-matter interactions allow both laser cooling and amplification. This represents a new tool to observe and control superfluid excitations that may provide insight into phonon-phonon interactions, quantized vortices and two-dimensional phenomena such as the Berezinskii-Kosterlitz-Thouless transition. The third sound modes studied here also offer a pathway towards quantum optomechanics with thin superfluid films, including the prospect of femtogram masses, high mechanical quality factors, strong phonon-phonon and phonon-vortex interactions, and self-assembly into complex geometries with sub-nanometre feature size.
Meraki, Adil; Mao, Shun; McColgan, Patrick T.; Boltnev, Roman E.; Lee, David M.; Khmelenko, Vladimir V.
2016-03-01
We studied the dynamics of thermoluminescence during destruction of porous structures formed by nanoclusters of nitrogen molecules containing high concentrations of stabilized nitrogen atoms. The porous structures were formed in bulk superfluid helium by injection of the products of discharges in nitrogen-helium gas mixtures through the liquid helium surface. Fast recombination of nitrogen atoms during warming-up led to explosive destruction of the porous structures accompanied by bright flashes. Intense emissions from the α -group of nitrogen atoms, the β -group of oxygen atoms and the Vegard-Kaplan bands of N_2 molecules were observed at the beginning of destruction. At the end of destruction the M- and β -bands of NO molecules as well as bands of O_2 molecules were also observed. Observation of the emissions from NO molecules at the end of destruction was explained by processes of accumulation of NO molecules in the system due to the large van der Waals interaction of NO molecules. For the first time, we observed the emission of the O_2 molecules at the end of destruction of the porous nitrogen structures as a result of the (NO)_2 dimer formation in solid nitrogen and subsequent processes leading to the appearance of excited O_2 molecules.
International Nuclear Information System (INIS)
We study the phase coherence property of Bose−Einstein condensates confined in a one-dimensional optical lattice formed by a standing-wave laser field. The lattice depth is determined using a method of Kapitza–Dirac scattering between a condensate and a short pulse lattice potential. Condensates are then adiabatically loaded into the optical lattice. The phase coherence property of the confined condensates is reflected by the interference patterns of the expanded atomic cloud released from the optical lattice. For weak lattice, nearly all of the atoms stay in a superfluid state. However, as the lattice depth is increased, the phase coherence of the whole condensate sample is gradually lost, which confirms that the sub-condensates in each lattice well have evolved into number-squeezed states. (atomic and molecular physics)
Gurzadyan, V G
2016-01-01
Within the scheme of conformal cyclic cosmology (CCC), information can be transmitted from aeon to aeon. Accordingly, the "Fermi paradox" and the SETI programme - of communication by remote civilizations - may be examined from a novel perspective: such information could, in principle, be encoded in the cosmic microwave background. The current empirical status of CCC is also discussed.
Gurzadyan, V. G.; Penrose, R.
2016-01-01
Within the scheme of conformal cyclic cosmology (CCC), information can be transmitted from aeon to aeon. Accordingly, the "Fermi paradox" and the SETI programme --of communication by remote civilizations-- may be examined from a novel perspective: such information could, in principle, be encoded in the cosmic microwave background. The current empirical status of CCC is also discussed.
International Nuclear Information System (INIS)
Part I. The Galitskii approach to the calculation of self-energies is used to find the energy barrier opposing the penetration of electrons into liquid helium, neon, and argon. This energy is computed to second order in the s-wave scattering length using the liquid structure factor to describe the actual two-body correlations in the host liquid. Typical barrier energies for helium-four and helium-three are 0.97 eV and 0.67 eV. Dielectric screening corrections to the e-atom interaction are included for the cases of neon and argon. The method of variable phase is used to compute effective scattering lengths that account for the screening. Typical barrier energies for neon and argon are 0.50 eV and -0.45 eV. Part II. The predictions for the dielectric behavior of superfluid helium-three A are reviewed in detail. A molecular model is proposed to improve the description of the interaction between two polarized helium atoms. This model predicts a twenty percent decrease in the magnitude of the dielectric shifts due to superfluid pairing, but it does not alter their qualitative behavior. Finally, an experiment is proposed that could measure the renormalization factor (R2) of Fomin, Pethick, and Serene
A compact copper nuclear demagnetization cryostat and a search for superfluidity in solid 4He
International Nuclear Information System (INIS)
The subject of this thesis is the theoretical and experimental study of matter at low temperatures, and the development of techniques to reach and measure these temperatures. A copper nuclear demagnetization cryostat was developed in order to reach low temperatures. This system distinguishes itself from other cryostats by its compact construction. The lowest temperature recorded by a pulsed Pt-NMR thermometer was 115 μK. This system was used to search for superfluidity in solid 4He. Due to the large zero-point motion of the atoms, 4He remains liquid down to zero temperature; a pressure of 25.3 bar is needed to force the atoms in a lattice. Even in solid state, the 4He atoms remain very mobile, changing lattice sites at a frequency of approximately 107 Hz. It is possible that solid 4He contains vacancies at zero temperature. These zero point vacancies are expected to behave like a gas of bosons, and should Bose-condense at some temperature. From experiments the upper limit to the vacancy concentration is set of 4·10-5. (author). 217 refs.; 46 figs.; 2 tabs
Superfluid-insulator transitions of two-species bosons in an optical lattice
International Nuclear Information System (INIS)
We consider the two-species bosonic Hubbard model with variable interspecies interaction and hopping strength in the grand canonical ensemble with a common chemical potential. We analyze the superfluid-insulator (SI) transition for the relevant parameter regimes and compute the ground state phase diagram in the vicinity of odd filling Mott states. We find that the superfluid-insulator transition occurs with (a) simultaneous onset of superfluidity of both species or (b) coexistence of Mott insulating state of one species and superfluidity of the other or, in the case of unit filling (c) complete depopulation of one species. The superfluid-insulator transition can be first order in a large region of the phase diagram. We develop a variational mean-field method which takes into account the effect of second order quantum fluctuations on the superfluid-insulator transition and corroborate the mean-field phase diagram using a quantum Monte Carlo study
Non-Riemannian effective spacetime effects on Hawking radiation in superfluids
Garcia de Andrade, L C
2005-01-01
Riemannian effective spacetime description of Hawking radiation in $^{3}He-A$ superfluids is extended to non-Riemannian effective spacetime. An example is given of non-Riemannian effective geometry of the rotational motion of the superfluid vacuum around the vortex where the effective spacetime Cartan torsion can be associated to the Hawking giving rise to a physical interpretation of effective torsion recently introduced in the literature in the form of an acoustic torsion in superfluid $^{4}He$ (PRD-70(2004),064004). Curvature and torsion singularities of this $^{3}He-A$ fermionic superfluid are investigated. This Lense-Thirring effective metric, representing the superfluid vacuum in rotational motion, is shown not support Hawking radiation when the isotropic $^{4}He$ is restored at far distances from the vortex axis. Hawking radiation can be expressed also in topological solitons (moving domain walls) in fermionic superfluids in non-Riemannian (teleparallel) $(1+1)$ dimensional effective spacetime. A telep...
International Nuclear Information System (INIS)
Superfluidity and phase separation in 3He-4He mixtures immersed in a jungle-gym (nonrandom) aerogel are studied by renormalization-group theory. Phase diagrams are calculated for a variety of aerogel concentrations. Superfluidity at very low 4He concentrations and a depressed tricritical temperature are found at the onset of superfluidity. A superfluid-superfluid phase separation, terminating at an isolated critical point, is found entirely within the superfluid phase. These phenomena and trends with respect to aerogel concentration are explained by the connectivity and tenuousness of a jungle-gym aerogel. copyright 1997 The American Physical Society
Energy Technology Data Exchange (ETDEWEB)
Mills, R.L. [BlackLight Power, Inc., Cranbury, NJ (United States)
2001-10-01
The Schroedinger equation was originally postulated in 1926 as having a solution of the one electron atom. It gives the principal energy levels of the hydrogen atom as eigenvalues of eigenfunction solutions of the Laguerre differential equation. But, as the principal quantum number n>>1, the eigenfunctions become nonsensical. Despite its wide acceptance, on deeper inspection, the Schroedinger solution is plagued with many failings as well as difficulties in terms of a physical interpretation that have caused it to remain controversial since its inception. Only the one electron atom may be solved without approximations, but it fails to predict electron spin and leads to models with nonsensical consequences such as negative energy states of the vacuum, infinities, and negative kinetic energy. In addition to many predictions which simply do not agree with observations, the Schroedinger equation predicts noncausality, nonlocality, spooky actions at a distance or quantum telepathy, perpetual motion, and many internal inconsistencies where contradicting statements have to be taken true simultaneously. Recently, the behavior of free electrons in superfluid helium has again forced the issue of the meaning of the wave function. Electrons form bubbles in superfluid helium which reveal that the electron is real and that a physical interpretation of the wave function is necessary. Furthermore, when irradiated with light of energy of about a 0.5 to several electron volts (H.J. Marris, J. Low Temp. Phys. 120 (2000) 173), the electrons carry current at different rates as if they exist with different sizes. It has been proposed that the behavior of free electrons in superfluid helium can be explained in terms of the electron breaking into pieces at superfluid helium temperatures (H.J. Marris, J. Low Temp. Phys. 120 (2000) 173). Yet, the electron has proven to be indivisible even under particle accelerator collisions at 90 GeV (LEPII). The nature of the wave function must now be
Quantum Effects of Uniform Bose Atomic Gases with Weak Attraction
Institute of Scientific and Technical Information of China (English)
CHENG Ze
2011-01-01
@@ We find that uniform Bose atomic gases with weak attraction can undergo a Bardeen-Cooper-Schrieffer(BCS)condensation below a critical temperature.In the BCS condensation state,bare atoms with opposite wave vectors are bound into pairs,and unpaired bare atoms are transformed into a new kind of quasi-particles,i.e.the dressed atoms.The atom-pair system is a condensate or a superfluid and the dressed-atom system is a normal fluid.The critical temperature and the effective mass of dressed atoms are derived analytically.The transition from the BCS condensation state to the normal state is a first-order phase transition.%We find that uniform Bose atomic gases with weak attraction can undergo a Bardeen-Cooper-Schrieffer (BCS)condensation below a critical temperature. In the BCS condensation state, bare atoms with opposite wave vectors are bound into pairs, and unpaired bare atoms are transformed into a new kind of quasi-particles, i.e. the dressed atoms. The atom-pair system is a condensate or a superfluid and the dressed-atom system is a normal fluid. The critical temperature and the effective mass of dressed atoms are derived analytically. The transition from the BCS condensation state to the normal state is a first-order phase transition.
Enrico Fermi and the Dolomites
Battimelli, Giovanni; de Angelis, Alessandro
2014-11-01
Summer vacations in the Dolomites were a tradition among the professors of the Faculty of Mathematical and Physical Sciences at the University of Roma since the end of the XIX century. Beyond the academic walls, people like Tullio Levi-Civita, Federigo Enriques and Ugo Amaldi sr., together with their families, were meeting friends and colleagues in Cortina, San Vito, Dobbiaco, Vigo di Fassa and Selva, enjoying trekking together with scientific discussions. The tradition was transmitted to the next generations, in particular in the first half of the XX century, and the group of via Panisperna was directly connected: Edoardo Amaldi, the son of the mathematician Ugo sr., rented at least during two summers, in 1925 and in 1949, and in the winter of 1960, a house in San Vito di Cadore, and almost every year in the Dolomites; Enrico Fermi was a frequent guest. Many important steps in modern physics, in particular the development of the Fermi-Dirac statistics and the Fermi theory of beta decay, are related to scientific discussions held in the region of the Dolomites.
Enrico Fermi and the Dolomites
International Nuclear Information System (INIS)
Summer vacations in the Dolomites were a tradition among the professors of the Faculty of Mathematical and Physical Sciences at the University of Roma since the end of the XIX century. Beyond the academic walls, people like Tullio Levi-Civita, Federigo Enriques and Ugo Amaldi sr., together with their families, were meeting friends and colleagues in Cortina, San Vito, Dobbiaco, Vigo di Fassa and Selva, enjoying trekking together with scientific discussions. The tradition was transmitted to the next generations, in particular in the first half of the XX century, and the group of via Panisperna was directly connected: Edoardo Amaldi, the son of the mathematician Ugo sr., rented at least during two summers, in 1925 and in 1949, and in the winter of 1960, a house in San Vito di Cadore, and almost every year in the Dolomites; Enrico Fermi was a frequent guest. Many important steps in modern physics, in particular the development of the Fermi-Dirac statistics and the Fermi theory of beta decay, are related to scientific discussions held in the region of the Dolomites
Fermi coordinates and Penrose limits
Energy Technology Data Exchange (ETDEWEB)
Blau, Matthias; Frank, Denis; Weiss, Sebastian [Institut de Physique, Universite de Neuchatel Rue Breguet 1, CH-2000 Neuchatel (Switzerland)
2006-06-07
We propose a formulation of the Penrose plane wave limit in terms of null Fermi coordinates. This provides a physically intuitive (Fermi coordinates are direct measures of geodesic distance in spacetime) and manifestly covariant description of the expansion around the plane wave metric in terms of components of the curvature tensor of the original metric, and generalizes the covariant description of the lowest order Penrose limit metric itself, obtained in Blau et al (2004 Class. Quantum Grav. 21 L43-9). We describe in some detail the construction of null Fermi coordinates and the corresponding expansion of the metric, and then study various aspects of the higher order corrections to the Penrose limit. In particular, we observe that in general the first-order corrected metric is such that it admits a light-cone gauge description in string theory. We also establish a formal analogue of the Weyl tensor peeling theorem for the Penrose limit expansion in any dimension, and we give a simple derivation of the leading (quadratic) corrections to the Penrose limit of AdS{sub 5} x S{sup 5}.
Enrico Fermi and the Dolomites
Battimelli, Giovanni
2014-01-01
Summer vacations in the Dolomites were a tradition among the professors of the Faculty of Mathematical and Physical Sciences at the University of Roma since the end of the XIX century. Beyond the academic walls, people like Tullio Levi-Civita, Federigo Enriques and Ugo Amaldi sr., together with their families, were meeting friends and colleagues in Cortina, San Vito, Dobbiaco, Vigo di Fassa and Selva, enjoying trekking together with scientific discussions. The tradition was transmitted to the next generations, in particular in the first half of the XX century, and the group of via Panisperna was directly connected: Edoardo Amaldi, the son of the mathematician Ugo sr., rented at least during two summers, in 1925 and in 1949, and in the winter of 1960, a house in San Vito di Cadore, and almost every year in the Dolomites; Enrico Fermi was a frequent guest. Many important steps in modern physics, in particular the development of the Fermi-Dirac statistics and the Fermi theory of beta decay, are related to scient...
Fermi Timing and Synchronization System
Energy Technology Data Exchange (ETDEWEB)
Wilcox, R.; Staples, J.; Doolittle, L.; Byrd, J.; Ratti, A.; Kaertner, F.X.; Kim, J.; Chen, J.; Ilday, F.O.; Ludwig, F.; Winter, A.; Ferianis, M.; Danailov, M.; D' Auria, G.
2006-07-19
The Fermi FEL will depend critically on precise timing of its RF, laser and diagnostic subsystems. The timing subsystem to coordinate these functions will need to reliably maintain sub-100fs synchronicity between distant points up to 300m apart in the Fermi facility. The technology to do this is not commercially available, and has not been experimentally demonstrated in a working facility. Therefore, new technology must be developed to meet these needs. Two approaches have been researched by different groups working with the Fermi staff. At MIT, a pulse transmission scheme has been developed for synchronization of RF and laser devices. And at LBL, a CW transmission scheme has been developed for RF and laser synchronization. These respective schemes have advantages and disadvantages that will become better understood in coming years. This document presents the work done by both teams, and suggests a possible system design which integrates them both. The integrated system design provides an example of how choices can be made between the different approaches without significantly changing the basic infrastructure of the system. Overall system issues common to any synchronization scheme are also discussed.
Fermi Timing and Synchronization System
International Nuclear Information System (INIS)
The Fermi FEL will depend critically on precise timing of its RF, laser and diagnostic subsystems. The timing subsystem to coordinate these functions will need to reliably maintain sub-100fs synchronicity between distant points up to 300m apart in the Fermi facility. The technology to do this is not commercially available, and has not been experimentally demonstrated in a working facility. Therefore, new technology must be developed to meet these needs. Two approaches have been researched by different groups working with the Fermi staff. At MIT, a pulse transmission scheme has been developed for synchronization of RF and laser devices. And at LBL, a CW transmission scheme has been developed for RF and laser synchronization. These respective schemes have advantages and disadvantages that will become better understood in coming years. This document presents the work done by both teams, and suggests a possible system design which integrates them both. The integrated system design provides an example of how choices can be made between the different approaches without significantly changing the basic infrastructure of the system. Overall system issues common to any synchronization scheme are also discussed
Enrico Fermi and the Dolomites
Energy Technology Data Exchange (ETDEWEB)
Battimelli, Giovanni, E-mail: giovanni.battimelli@uniroma1.it; Angelis, Alessandro de, E-mail: alessandro.de.angelis@cern.ch
2014-11-15
Summer vacations in the Dolomites were a tradition among the professors of the Faculty of Mathematical and Physical Sciences at the University of Roma since the end of the XIX century. Beyond the academic walls, people like Tullio Levi-Civita, Federigo Enriques and Ugo Amaldi sr., together with their families, were meeting friends and colleagues in Cortina, San Vito, Dobbiaco, Vigo di Fassa and Selva, enjoying trekking together with scientific discussions. The tradition was transmitted to the next generations, in particular in the first half of the XX century, and the group of via Panisperna was directly connected: Edoardo Amaldi, the son of the mathematician Ugo sr., rented at least during two summers, in 1925 and in 1949, and in the winter of 1960, a house in San Vito di Cadore, and almost every year in the Dolomites; Enrico Fermi was a frequent guest. Many important steps in modern physics, in particular the development of the Fermi-Dirac statistics and the Fermi theory of beta decay, are related to scientific discussions held in the region of the Dolomites.
Cai, Rong-Gen; Wu, Yue-Liang; Zhang, Yun-Long
2016-01-01
In this paper we investigate the $(2+1)$-dimensional topological non-Fermi liquid in strongly correlated electron system, which has a holographic dual description by Einstein gravity in $(3+1)$-dimensional anti-de Sitter (AdS) space-time. In a dyonic Reissner-Nordstrom black hole background, we consider a Dirac fermion coupled to the background $U(1)$ gauge theory and an intrinsic chiral gauge field $b_M$ induced by chiral anomaly. UV retarded Green's function of the charged fermion in the UV boundary from AdS$_4$ gravity is calculated, by imposing in-falling wave condition at the horizon. We also obtain IR correlation function of the charged fermion at the IR boundary arising from the near horizon geometry of the topological black hole with index $k=0,\\pm 1$. By using the UV retarded Green's function and IR correlation function, we analyze the low frequency behavior of the topological non-Fermi liquid at zero and finite temperatures, especially the relevant non-Fermi liquid behavior near the quantum critical...
Superfluid behavior of a Bose–Einstein condensate in a random potential
International Nuclear Information System (INIS)
We investigate the relation between Bose–Einstein condensation (BEC) and superfluidity in the ground state of a one-dimensional model of interacting bosons in a strong random potential. We prove rigorously that in a certain parameter regime the superfluid fraction can be arbitrarily small while complete BEC prevails. In another regime there is both complete BEC and complete superfluidity, despite the strong disorder. (paper)
Neutrino Emissivity of Non-equilibrium beta processes With Nucleon Superfluidity
Pi, Chun-Mei; Zheng, Xiao-Ping; Yang, Shu-Hua
2009-01-01
We investigate the influence of nucleon superfluidity on the neutrino emissivity of non-equilibrium beta processes. Calculations are performed of the reduction factors for direct and modified Urca processes with three types of nucleon superfluidity in $npe$ matter. The numerical results are given since the analytical solution is impossible. We find that the behavior of the superfluid influence is closely related to the chemical departure from beta equilibrium. For small chemical departure, th...
Fermi acceleration of Lyman-alpha photons by shocks
Neufeld, David A.; Mckee, Christopher F.
1988-01-01
The repeated scattering of Ly-alpha radiation across a shock front results in a systematic blueshift which may greatly exceed the shock velocity vs and is proportional to cube root of (Nvs), where N is the column density of hydrogen atoms on either side of the shock front. The blueshifting process is similar to the Fermi acceleration of cosmic rays and may be responsible for the blue asymmetric line profiles that have been observed in high-redshift Ly-alpha galaxies. The Ly-alpha line profile in 3C 326.1 is accounted for by a model in which shocks, driven into a population of interstellar clouds by a radio lobe, trigger the formation of ionizing stars and Fermi accelerate the Ly-alpha radiation emitted by H II regions surrounding those stars. Galaxy mergers, particularly between galaxies with low dust content, should produce Ly-alpha lines with strong blue wings.
Fermi acceleration of Lyman-alpha photons by shocks
International Nuclear Information System (INIS)
The repeated scattering of Ly-alpha radiation across a shock front results in a systematic blueshift which may greatly exceed the shock velocity vs and is proportional to cube root of (Nvs), where N is the column density of hydrogen atoms on either side of the shock front. The blueshifting process is similar to the Fermi acceleration of cosmic rays and may be responsible for the blue asymmetric line profiles that have been observed in high-redshift Ly-alpha galaxies. The Ly-alpha line profile in 3C 326.1 is accounted for by a model in which shocks, driven into a population of interstellar clouds by a radio lobe, trigger the formation of ionizing stars and Fermi accelerate the Ly-alpha radiation emitted by H II regions surrounding those stars. Galaxy mergers, particularly between galaxies with low dust content, should produce Ly-alpha lines with strong blue wings. 14 references
Small metal particles and the ideal Fermi gas
International Nuclear Information System (INIS)
Kubo's theoretical model of a small metal particle consists of a number of noninteraction electrons (an ideal Fermi gas) confined to a finite volume. By 'small' it meant that the size of the particle is intermediate between that of a few atoms cluster and the bulk solid, the radius of the particle being 5 to 50 Angstroms. The model is discussed and size dependence of various energy scales is studied. For a fermi gas confined in a sphere or a cube, two size-dependent energy scales are important. The inner scale δ is the mean spacing between successive energy levels. It governs the very low temperature behaviour. The outer scale Δ is associated with the shell structure when δ ≤T<Δ, thermodynamic properties show an oscillatory fluctuations around a smooth background as the size or energy is varied. (M.G.B.) 23 refs
Superfluid-like dynamics in active vortex fluids
Slomka, Jonasz; Dunkel, Jorn
Active biological fluids exhibit rich non-equilibrium dynamics and share striking similarities with quantum fluids, from vortex formation and magnetic ordering to superfluid-like behavior. Building on universality ideas, we have recently proposed a generalization of the Navier-Stokes equations that captures qualitatively the active bulk flow structures observed in bacterial suspensions. Here, we present new numerical simulations that explicitly account for boundary and shear effects. The theory successfully reproduces recent experimental observations of bacterial suspensions, including a superfluid-like regime of nearly vanishing shear viscosity. Our simulations further predict a geometry-induced 'quantization' of viscosity and the existence of excited states capable of performing mechanical work. It is plausible that these results generalize to a broad a class of fluids that are subject to an active scale selection mechanism.
Hydrodynamics of superfluid helium in a single nanohole.
Savard, M; Dauphinais, G; Gervais, G
2011-12-16
The flow of liquid helium through a single nanohole with radius smaller than 25 nm was studied. Mass flow was induced by applying a pressure difference of up to 1.4 bar across a 50 nm thick Si(3)N(4) membrane and was measured directly by means of mass spectrometry. In liquid He I, we experimentally show that the fluid is not clamped by the short pipe with diameter-to-length ratio D/L≃1, despite the small diameter of the nanohole. This viscous flow is quantitatively understood by making use of a model of flow in short pipes. In liquid He II, a two-fluid model for mass flow is used to extract the superfluid velocity in the nanohole for different pressure heads at temperatures close to the superfluid transition. These velocities compare well to existing data for the critical superflow of liquid helium in other confined systems. PMID:22243081
Superfluid orifice pulse tube refrigerator below 1 kelvin
International Nuclear Information System (INIS)
Half the moving parts of the superfluid Stirling refrigerator have been eliminated by adopting an orifice-pulse-tube configuration. The authors first such device has cooled to 0.64 K with the hot platform anchored at 1.0 K. Performance of the refrigerator is in reasonable agreement with expectations. Two curious features of the superfluid pulse tube are in distinct contrast with features of conventional pulse tubes. First, stability of the 3He-4He mixture against free convection requires that the hot end of the pulse tube must be below the cold end. Second, the low heat capacity of metals below 1 K makes heat loss along the pulse tube due to the fluid's oscillatory motion very small
Spatial Relevancies of Hybrid Systems Relates to Superfluid
Hidajatullah-Widastra, Fatahillah
2015-05-01
After S/F hybrid system from Martin Lange, of spatial modulation Superconductor-Electromagnet hybrids superconductor producing studies conclusion, for superconductor at large Hand/or T(i.e close to the phase transitionline), when the superfluid densitiy tends to 0. Further as for He3-B superfluid ``testing ground'', after sought extensometer for every materials testing application from , in K Matsumoto:``Flux pinning Engineering for Application of HTS'', 2013 quote Higgs boson , whereas it plays role as similar phenomena of Meissner effect, both involves magnet levitating. Accompanying Gosowong vein, US 16. 3 Million costed study-report who said the toxic waste also endangering biodiversity[Dini Septanti: ``The BUYAT Case: Straddling between Environmental Securitization & De-securitization'', herewith proposed the ``complexity systems'' comparison comprises also phase transition & ``directed polymer'' notions of JP Bouchaud et al: ``Wealth condensation in a simple model of economy''. Incredibles acknowledgment to HE. Mr. Drs. P. SWANTORO & HE.Mr.Ir. H. ABURIZAL BAKRIE.
Vortex structure in rotational state superfluid 3He
International Nuclear Information System (INIS)
The structure of vortices in rotational superfluid 3He is considered. It is marked that in the A-phase quantum vortices are possible, in which the A-phase superfluid state is never disturbed. As a consequence of a discrete combined invariance (calibration transformation plus rotation of a spin subsystem) one more exotic type of vortices is possible in the A-phase. This is a hybrid of disclination in a magnetic anisotropy vector field d (with a half-integer Frank index) and vortex that possesses a half-integer number of circulation quanta. Such vortices can be observed at rotation of the A-phase confined between parallel plates. The vortex properties in the B-phase are determined by a continuous combined symmetry. The calculations show the vortex in the β-phase at low pressures to be in the ν-state. The vortices considered are observed in the NMR experiments
Lifshitz effects on holographic p-wave superfluid
Directory of Open Access Journals (Sweden)
Ya-Bo Wu
2015-02-01
Full Text Available In the probe limit, we numerically build a holographic p-wave superfluid model in the four-dimensional Lifshitz black hole coupled to a Maxwell-complex vector field. We observe the rich phase structure and find that the Lifshitz dynamical exponent z contributes evidently to the effective mass of the matter field and dimension of the gravitational background. Concretely, we obtain that the Cave of Winds appeared only in the five-dimensional anti-de Sitter (AdS spacetime, and the increasing z hinders not only the condensate but also the appearance of the first-order phase transition. Furthermore, our results agree with the Ginzburg–Landau results near the critical temperature. In addition, the previous AdS superfluid model is generalized to the Lifshitz spacetime.
From Field Theory to the Hydrodynamics of Relativistic Superfluids
Stetina, Stephan
2015-01-01
The hydrodynamic description of a superfluid is usually based on a two-fluid picture. In this thesis, basic properties of such a relativistic two-fluid system are derived from the underlying microscopic physics of a complex scalar quantum field theory. To obtain analytic results of all non-dissipative hydrodynamic quantities in terms of field theoretic variables, calculations are first carried out in a low-temperature and weak-coupling approximation. In a second step, the 2-particle-irreducible formalism is applied: This formalism allows for a numerical evaluation of the hydrodynamic parameters for all temperatures below the critical temperature. In addition, a system of two coupled superfluids is studied. As an application, the velocities of first and second sound in the presence of a superflow are calculated. The results show that first (second) sound evolves from a density (temperature) wave at low temperatures to a temperature (density) wave at high temperatures. This role reversal is investigated for ult...
Transport and extraction of radioactive ions stopped in superfluid helium
Huang Wan Xia; Gloos, K; Takahashi, N; Arutyunov, K; Pekola, J P; Äystö, J
2003-01-01
A new approach to convert a high energy beam to a low energy one, which is essential for the next generation radioactive ion beam facilities, has been proposed and tested at Jyvaeskylae, Finland. An open sup 2 sup 2 sup 3 Ra alpha-decay-recoil source has been used to produce radioactive ions in superfluid helium. The alpha spectra demonstrate that the recoiling sup 2 sup 1 sup 9 Rn ions have been extracted out of liquid helium. This first observation of the extraction of heavy positive ions across the superfluid helium surface was possible thanks to the high sensitivity of radioactivity detection. An efficiency of 36% was obtained for the ion extraction out of liquid helium.
Communication: Electron diffraction of ferrocene in superfluid helium droplets
Zhang, Jie; He, Yunteng; Kong, Wei
2016-06-01
We report electron diffraction of ferrocene doped in superfluid helium droplets. By taking advantage of the velocity slip in our pulsed droplet beam using a pulsed electron gun, and by doping with a high concentration of ferrocene delivered via a pulsed valve, we can obtain high quality diffraction images from singly doped droplets. Under the optimal doping conditions, 80% of the droplets sampled in the electron beam are doped with just one ferrocene molecule. Extension of this size selection method to dopant clusters has also been demonstrated. However, incomplete separation of dopant clusters might require deconvolution and modeling of the doping process. This method can be used for studies of nucleation processes in superfluid helium droplets.
Lifshitz effects on holographic p-wave superfluid
Energy Technology Data Exchange (ETDEWEB)
Wu, Ya-Bo, E-mail: ybwu61@163.com; Lu, Jun-Wang; Zhang, Cheng-Yuan; Zhang, Nan; Zhang, Xue; Yang, Zhuo-Qun; Wu, Si-Yu
2015-02-04
In the probe limit, we numerically build a holographic p-wave superfluid model in the four-dimensional Lifshitz black hole coupled to a Maxwell-complex vector field. We observe the rich phase structure and find that the Lifshitz dynamical exponent z contributes evidently to the effective mass of the matter field and dimension of the gravitational background. Concretely, we obtain that the Cave of Winds appeared only in the five-dimensional anti-de Sitter (AdS) spacetime, and the increasing z hinders not only the condensate but also the appearance of the first-order phase transition. Furthermore, our results agree with the Ginzburg–Landau results near the critical temperature. In addition, the previous AdS superfluid model is generalized to the Lifshitz spacetime.
An introduction to the theory of superfluid turbulence
International Nuclear Information System (INIS)
In this paper I first describe some aspects of the theory of counterflow turbulence. I then devote most of the paper to grid turbulence, where the theory is less well developed, although I make use of an important experimental result obtained with a more complicated type of flow generated by two counter-rotating discs. My aim is to stimulate interest in the theory of superfluid turbulence, particularly, at this stage, in the simple case of grid turbulence, among both low temperature physicists and those with a background in classical fluid mechanics. I focus on open questions and unsolved problems, questions and problems that are clearly seen in grid turbulence, but which are more widely relevant. My own background is in experimental quantum fluids. I tend to speculate about what I see as the physics of superfluid turbulence. (orig.)
Communication: Electron diffraction of ferrocene in superfluid helium droplets.
Zhang, Jie; He, Yunteng; Kong, Wei
2016-06-14
We report electron diffraction of ferrocene doped in superfluid helium droplets. By taking advantage of the velocity slip in our pulsed droplet beam using a pulsed electron gun, and by doping with a high concentration of ferrocene delivered via a pulsed valve, we can obtain high quality diffraction images from singly doped droplets. Under the optimal doping conditions, 80% of the droplets sampled in the electron beam are doped with just one ferrocene molecule. Extension of this size selection method to dopant clusters has also been demonstrated. However, incomplete separation of dopant clusters might require deconvolution and modeling of the doping process. This method can be used for studies of nucleation processes in superfluid helium droplets. PMID:27305988
A Neutron Scattering Study of Collective Excitations in Superfluid Helium
DEFF Research Database (Denmark)
Graf, E. H.; Minkiewicz, V. J.; Bjerrum Møller, Hans;
1974-01-01
Extensive inelastic-neutron-scattering experiments have been performed on superfluid helium over a wide range of energy and momentum transfers. A high-resolution study has been made of the pressure dependence of the single-excitation scattering at the first maximum of the dispersion curve over the...... range 1-24.4 atm and at 1 atm of the wave-vector dependence of the single-excitation scattering beyond the roton minimum. The latter data, but not the former, are consistent with the idea of an instability threshold suggested by Pitaevskii and by Enz. The pressure and wave-vector dependence of the...... multiexcitation scattering was also studied. It is shown that the multiphonon spectrum of a simple Debye solid with the phonon dispersion and single-excitation cross section of superfluid helium qualitatively reproduces these data....
Reconnection dynamics and normal fluid mutual friction in superfluid turbulence
Laurie, Jason
2014-01-01
We investigate the forcing of the normal fluid via mutual friction in finite temperature superfluid turbulence in helium-4, paying particular attention to the role of quantized vortex reconnections. Through the use of the vortex filament model, we produce three experimentally relevant vortex tangles each with different topological properties in steady state conditions. Subsequently we investigate, through statistical analysis, how the mutual friction force upon the normal fluid is affected by the characteristic of each of the vortex tangles. Finally, by monitoring the vortex reconnection events, we show how reconnections produce areas of relatively high curvature and superfluid velocity leading to regions of high normal fluid mutual friction, particularly for the homogeneous and isotropic tangles.
Coherent magneto-elastic oscillations in superfluid magnetars
Gabler, Michael; Stergioulas, Nikolaos; Font, José A; Müller, Ewald
2016-01-01
We study the effect of superfluidity on torsional oscillations of highly magnetised neutron stars (magnetars) with a microphysical equation of state by means of two-dimensional, magnetohydrodynamical- elastic simulations. The superfluid properties of the neutrons in the neutron star core are treated in a parametric way in which we effectively decouple part of the core matter from the oscillations. Our simulations confirm the existence of two groups of oscillations, namely continuum oscillations that are confined to the neutron star core and are of Alfv\\'enic character, and global oscillations with constant phase and that are of mixed magneto-elastic type. The latter might explain the quasi-periodic oscillations observed in magnetar giant flares, since they do not suffer from the additional damping mechanism due to phase mixing, contrary to what happens for continuum oscillations. However, we cannot prove rigorously that the coherent oscillations with constant phase are normal modes. Moreover, we find no crust...
Transitions and excitations in a superfluid stream passing small impurities
Pinsker, Florian
2014-05-08
We analyze asymptotically and numerically the motion around a single impurity and a network of impurities inserted in a two-dimensional superfluid. The criticality for the breakdown of superfluidity is shown to occur when it becomes energetically favorable to create a doublet—the limiting case between a vortex pair and a rarefaction pulse on the surface of the impurity. Depending on the characteristics of the potential representing the impurity, different excitation scenarios are shown to exist for a single impurity as well as for a lattice of impurities. Depending on the lattice characteristics it is shown that several regimes are possible: dissipationless flow, excitations emitted by the lattice boundary, excitations created in the bulk, and the formation of large-scale structures.
Lifshitz effects on holographic p-wave superfluid
International Nuclear Information System (INIS)
In the probe limit, we numerically build a holographic p-wave superfluid model in the four-dimensional Lifshitz black hole coupled to a Maxwell-complex vector field. We observe the rich phase structure and find that the Lifshitz dynamical exponent z contributes evidently to the effective mass of the matter field and dimension of the gravitational background. Concretely, we obtain that the Cave of Winds appeared only in the five-dimensional anti-de Sitter (AdS) spacetime, and the increasing z hinders not only the condensate but also the appearance of the first-order phase transition. Furthermore, our results agree with the Ginzburg–Landau results near the critical temperature. In addition, the previous AdS superfluid model is generalized to the Lifshitz spacetime
Superfluid hydrodynamics in the inner crust of neutron stars
Martin, Noël
2016-01-01
The inner crust of neutron stars is supposed to be inhomogeneous and composed of dense structures (clusters) that are immersed in a dilute gas of unbound neutrons. Here we consider spherical clusters forming a BCC crystal and cylindrical rods arranged in a hexagonal lattice. We study the relative motion of these dense structures and the neutron gas using superfluid hydrodynamics. Within this approach, which relies on the assumption that Cooper pairs are small compared to the crystalline structures, we find that the entrainment of neutrons by the clusters is very weak since neutrons of the gas can flow through the clusters. Consequently, we obtain a low effective mass of the clusters and a superfluid density that is even higher than the density of unbound neutrons. Consequences for the constraints from glitch observations are discussed.
Oscillatory motion: quantum whistling in superfluid helium-4.
Hoskinson, E; Packard, R E; Haard, Thomas M
2005-01-27
Fundamental considerations predict that macroscopic quantum systems such as superfluids and the electrons in superconductors will undergo oscillatory motion when forced through a small constriction. Here we induce these oscillations in superfluid helium-4 (4He) by pushing it through an array of nanometre-sized apertures. The oscillations, which are detected as an audible whistling sound, obey the so-called Josephson frequency relation and occur coherently among all the apertures. The discovery of this property in 4He at the relatively high temperature of 2 K (2,000 times higher than the temperature at which a related but different phenomenon occurs in 3He) may pave the way for a new class of practical rotation sensors of unprecedented precision. PMID:15674281
Instabilities in relativistic two-component (super)fluids
Haber, Alexander; Stetina, Stephan
2016-01-01
We study two-fluid systems with nonzero fluid velocities and compute their sound modes, which indicate various instabilities. For the case of two zero-temperature superfluids we employ a microscopic field-theoretical model of two coupled bosonic fields, including an entrainment coupling and a non-entrainment coupling. We analyse the onset of the various instabilities systematically and point out that the dynamical two-stream instability can only occur beyond Landau's critical velocity, i.e., in an already energetically unstable regime. A qualitative difference is found for the case of two normal fluids, where certain transverse modes suffer a two-stream instability in an energetically stable regime if there is entrainment between the fluids. Since we work in a fully relativistic setup, our results are very general and of potential relevance for (super)fluids in neutron stars and, in the non-relativistic limit of our results, in the laboratory.
Atomic Bose and Anderson Glasses in Optical Lattices
Damski, B.; Zakrzewski, J.; Santos, L.; Zoller, P.; Lewenstein, M.
2003-08-01
An ultracold atomic Bose gas in an optical lattice is shown to provide an ideal system for the controlled analysis of disordered Bose lattice gases. This goal may be easily achieved under the current experimental conditions by introducing a pseudorandom potential created by a second additional lattice or, alternatively, by placing a speckle pattern on the main lattice. We show that, for a noncommensurable filling factor, in the strong-interaction limit, a controlled growing of the disorder drives a dynamical transition from superfluid to Bose-glass phase. Similarly, in the weak interaction limit, a dynamical transition from superfluid to Anderson-glass phase may be observed. In both regimes, we show that even very low-intensity disorder-inducing lasers cause large modifications of the superfluid fraction of the system.
The onset of superfluidity in thin films of 4He adsorbed on ordered and disordered substrates
International Nuclear Information System (INIS)
The authors have completed a systematic study of the superfluid density of 4He films adsorbed on two substrates: exfoliated basal-plane graphite and 91% porosity aerogel glass. The authors measurements demonstrate a dramatic difference in the coverage-dependence of the superfluid density in these two systems. The onset of superfluidity in the aerogel system is similar to that observed in the case of other disordered substrates such as Vycor glass and mylar. The superfluid density at zero temperature is nearly proportional to coverage once the critical coverage for superfluidity is exceeded. The superfluid density for films adsorbed on graphite does not evolve in this simple fashion. The onset of superfluidity appears to occur near two layers, but the superfluid density increases very rapidly between 2.5 and 3 layers. This coverage regime is also characterized by a dramatic sharpening density and transition temperature remain essentially unchanged as the coverage is increased. We will discuss in the context of recent theoretical work on the onset of superfluidity in model Bose systems
Heat Capacity of Superfluid (sup 4)He in the Presence of a Heat Current Near T
Chui, Talso C. P.; Goodstein, David L.; Harter, Alexa W.; Mukhopadhyay, Ranjan
1996-01-01
The thermodynamic theory of superfluid helium in the presence of a heat current is presented. We show that there is a thermodynamic relation between the heat capacity and the expression ps(W), which describes the depression of the superfluid density with the counterflow velocity W. Using this relation we show that the heat capacity of superfluid super4He in the presence of a heat current diverges at a depressed lambda transition temperature, suggesting the possibility of a new second order phase transition where the superfluid wave function is not the order parameter.
Collective modes in superfluid-superconducting neutron stars
Kobyakov, D.; Samuelsson, L; Marklund, M.; Lundh, E; Bychkov, V.; Brandenburg, A.
2015-01-01
The collective longitudinal modes of vibration of baryon density in uniform nuclear matter are considered in a regime where the electrons are ultrarelativistic and quantum-degenerate, and the nucleons are superfluid and superconducting. The equation of state of matter in the core of neutron stars is represented phenomenologically, based on the chiral effective field theory of nuclear interactions constrained by observations of neutron stars, and is matched to properties of nuclear matter in t...
Geometric Phase for Fermionic Quasiparticles Scattering by Disgyration in Superfluids
de Andrade, L. C. Garcia; Carvalho, A. M. de M.; Furtado, C.
2004-01-01
We consider a Volovik's analog model for description of a topological defects in a superfluid and we investigate the scattering of quasiparticles in this background. The analog of the gravitational Aharonov-Bohm in this system is found. An analysis of this problem employing loop variables is considered and corroborates for the existence of the Aharonov-Bohm effect in this system. The results presented here may be used to study the Aharonov-Bohm effect in superconductors.
Emergent Majorana mass and axion couplings in superfluids
International Nuclear Information System (INIS)
Axions (in the general sense) may acquire qualitatively new couplings inside superfluids. Their conventional couplings to fermions, in empty space, involve purely imaginary masses; the new couplings involve emergent Majorana masses. A generalized concept of Majorana mass is proposed, which allows continuous interpolation between Majorana and Dirac fermions, and also extension to bosons. The possibility of weak links for axions, recently put forward, is analyzed and replaced with a non-local analogue. (fast track communication)
Baryon superfluidity and neutrino emissivity of neutron stars
Takatsuka, T.; Tamagaki, R.
2004-01-01
For neutron stars with hyperon-mixed core, neutrino emissivity is studied under the equation of state, obtained by introducing repulsive three-body force universal for all baryons so as to assure the maximum mass compatible with the observation. By paying attention to the density-dependence of critical temperatures of baryon superfluids, which reflect the nature of baryon-baryon interaction and control neutron star cooling, we show what neutrino emission processes are efficient in the regions...
Emergent Geometric Hamiltonian and Insulator-Superfluid Phase Transitions
Zhou, Fei
2005-01-01
I argue that certain bosonic insulator-superfluid phase transitions as an interaction constant varies are driven by emergent geometric properties of insulating states. The {\\em renormalized} chemical potential and distribution of disordered bosons define the geometric aspect of an effective low energy Hamiltonian which I employ to study various resonating states and quantum phase transitions. In a mean field approximation, I also demonstrate that the quantum phase transitions are in the unive...
Generalized deformed oscillator for vortices in superfluid films
Bonatsos, Dennis; Daskaloyannis, C.
1997-01-01
The algebra of observables of a system of two identical vortices in a superfluid thin film is described as a generalized deformed oscillator with a structure function containing a linear (harmonic oscillator) term and a quadratic term. In contrast to the deformed oscillators occuring in other physical systems (correlated fermion pairs in a single-$j$ nuclear shell, Morse oscillator), this oscillator is not amenable to perturbative treatment and cannot be approximated by quons. From the mathem...
Fluctuations above the superfluid transition in liquid 3He
International Nuclear Information System (INIS)
It is shown that fluctuations above the superfluid transition in liquid 3He depend strongly upon the relative angular momentum l of a Cooper pair but are insensitive to the fourth order term in the Ginsburg-Landau free energy. The effects are shown to be observable in the static magnetization, viscosity and spin diffusion and give a means of determining the value of l. (U.S.)
Phase slippage in superfluid 3He-B
International Nuclear Information System (INIS)
We review some applications of the hydrodynamic Josephson effects. The relationship between the quantum mechanical phase difference along a micro-orifice and the flow through it is discussed in terms of a simple model which accounts for the observations performed in 3He-B above 0.7 Tc. Possible uses of the superfluid hydromechanical resonator as a sensitive and stable absolute gyrometer are described
Large Chern Number Topological Superfluids in Coupled Layer System
Huang, Beibing; Chan, Jeffrey Chun Fai; Ming GONG
2014-01-01
We investigate the topological phase transition with large Chern number in a coupled layer system. The topological transitions between different topological superfluids can be realized by controlling the binding energy, interlay tunneling and layer asymmetry {\\it etc}. These topological phase transitions can be characterized by energy gap closing and reopening at the critical points at zero momentum, where the Pfaffian and Chern number undergo a discontinuous change. The bulk-edge corresponde...
Spontaneous current in an holographic s+p superfluid
Arias, Raúl
2016-01-01
We study a Maxwell-Proca action in an asymptotically AdS black hole background. When moving the temperature of the black hole, we find rich phase diagrams having, that depend strongly on the dimension of the operator dual to the Proca field . We present different solutions in the bulk that correspond to the holographic dual for $s$, $p$ or $s+p$-wave superfluids. In the last case we observe the onset of a spontaneously induced current.
Spin-up problem in superfluid /sup 4/He
Energy Technology Data Exchange (ETDEWEB)
Adams, P.W.; Cieplak, M.; Glaberson, W.I.
1985-07-01
We report the results of an experimental investigation of the nature of the vortex-boundary interaction and its role in the spin-up problem of superfluid /sup 4/He. We find evidence for two independence vortex-drag mechanisms: a drag associated with vortex lines pulling against pinning sites with a force equal to the line ''tension'' and a viscous drag associated with vortex motion through the normal-fluid Ekman layers.
Spin-up problem in superfluid 4He
International Nuclear Information System (INIS)
We report the results of an experimental investigation of the nature of the vortex-boundary interaction and its role in the spin-up problem of superfluid 4He. We find evidence for two independence vortex-drag mechanisms: a drag associated with vortex lines pulling against pinning sites with a force equal to the line ''tension'' and a viscous drag associated with vortex motion through the normal-fluid Ekman layers
Superfluid helium boiling in porous structure under microgravity: model representation
International Nuclear Information System (INIS)
The results of model calculation of superfluid helium boiling under microgravity conditions are reported. The evolution of a vapour film on the cylindrical heater surface inside the porous thick walled structure is analyzed. The molecular-kinetic theory methods are used to describe heat and mass-transfer within helium interface. The equation of vapour-liquid interface motion is solved. The effect of experimental parameters on the vapour film properties is studied. The calculation data for microgravity and terrestrial conditions are compared