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Full-Text Articles in Physics

Observation Of Spin Rotation Effects In Polarized He-3-He-4 Mixtures, Wj Gully, Wj Mullin Feb 2011

Observation Of Spin Rotation Effects In Polarized He-3-He-4 Mixtures, Wj Gully, Wj Mullin

William J. Mullin

Quantum exchange effects, predicted to occur in the spin diffusion of polarized nondegenerate gases, have been observed in a 3He-4He mixture by spin-echo techniques. Measurements of the spin rotation parameter (μM0)2 and diffusion constant D are in reasonable agreement with theoretical predictions until the degeneracy temperature is approached.


Nonlocal Quantum Effects With Bose-Einstein Condensates, F Laloe, Wj Mullin Feb 2011

Nonlocal Quantum Effects With Bose-Einstein Condensates, F Laloe, Wj Mullin

William J. Mullin

Quantum systems in Fock states do not have a phase. When two or more Bose-Einstein condensates are sent into interferometers, they nevertheless acquire a relative phase under the effect of quantum measurements. The usual explanation relies on spontaneous symmetry breaking, where phases are ascribed to all condensates and treated as unknown classical quantities. However, this image is not always sufficient: when all particles are measured, quantum mechanics predicts probabilities that are sometimes in contradiction with it, as illustrated by quantum violations of local realism. In this Rapid communication, we show that interferometers can be used to demonstrate a large variety ...


Nonlinear Spin Dynamics Of Dilute He-3-He-4 At Very High B/T, H Akimoto, Ed Adams, D Candela, Wj Mullin, V Shvarts, Ns Sullivan, Js Xia Feb 2011

Nonlinear Spin Dynamics Of Dilute He-3-He-4 At Very High B/T, H Akimoto, Ed Adams, D Candela, Wj Mullin, V Shvarts, Ns Sullivan, Js Xia

William J. Mullin

We are conducting an experimental search for spin-diffusion anisotropy in dilute 3He–4He mixtures at very high B/T (17 T, 2 mK). Previous experiments have not reached sufficiently high B/T ratios to observe the effect in very dilute mixtures, for which quantitative theoretical predictions exist. The planned experiments will require NMR experiments at very high values of the dimensionless spin rotation parameter μM. We have performed numerical simulations of the nonlinear spin dynamics to assess the feasibility of spin-wave and spin-echo experiments.


Viscosity Of Highly Polarized Very Dilute He-3-He-4 Mixtures, H Akimoto, Js Xia, Ed Adams, D Candela, Wj Mullin, Ns Sullivan Feb 2011

Viscosity Of Highly Polarized Very Dilute He-3-He-4 Mixtures, H Akimoto, Js Xia, Ed Adams, D Candela, Wj Mullin, Ns Sullivan

William J. Mullin

We present vibrating - wire viscosity measurements on a very dilute 3He-4He mixture (X3 = 150 ppm) in fields up to 14.8 T and temperatures down to 3 mK. The 3He spin polarization is greater than 99% for the highest field and lowest temperature used. In these conditions, the s-wave scattering rate decreases due to a lack of quasiparticles with the minority spin state. This enhances all transport coefficients including the viscosity. At the lowest temperature, the hydrodynamic damping of the viscometer in a 14.8 T field was more than 10 times larger than in low fields. This indicates a ...


Longitudinal And Transverse Spin Diffusion In Polarized He-3-He-4 Solutions, Jw Jeon, Wj Mullin Feb 2011

Longitudinal And Transverse Spin Diffusion In Polarized He-3-He-4 Solutions, Jw Jeon, Wj Mullin

William J. Mullin

Spin dynamics for arbitrarily polarized and very dilute 3He-4He solutions are described. We generalize previous work to include 3He-4He phenomenological interactions, and we calculate longitudinal and transverse spin diffusion coefficients and the identical-particle spin-rotation parameter. Good agreement is found in comparison with recent data. The s-wave approximation is found to be inadequate and mean-field corrections are important.


Bose-Einstein Condensation In A Harmonic Potential, Wj Mullin Feb 2011

Bose-Einstein Condensation In A Harmonic Potential, Wj Mullin

William J. Mullin

We examine several features of Bose-Einstein condensation (BEC) in an external harmonic potential well. In the thermodynamic limit, there is a phase transition to a spatial Bose-Einstein condensed state for dimensionD≥2. The thermodynamic limit requires maintaining constant average density by weakening the potential while increasing the particle numberN to infinity, while of course in real experiments the potential is fixed andN stays finite. For such finite ideal harmonic systems we show that a BEC still occurs, although without a true phase transition, below a certain “pseudo-critical” temperature, even forD=1. We study the momentum-space condensate fraction and find that ...


A Study Of Bose-Einstein Condensation In A Two-Dimensional Trapped Gas, Wj Mullin Feb 2011

A Study Of Bose-Einstein Condensation In A Two-Dimensional Trapped Gas, Wj Mullin

William J. Mullin

We examine the possibility of Bose-Einstein condensation (BEC) in two-dimensional (2D) system of interacting particles in a trap. We use a self-consistent mean-field theory of Bose particles interacting by a contact interaction in the Popov and WKB approximations. The equations show that the normal state has a phase transition at some critical temperature T c but below T c the Bose-Einstein condensed state is not a consistent solution of the equations in the thermodynamic limit. This result agrees with a theorem recently discussed by the author that shows that a BEC state is impossible for an interacting gas in a ...


Beyond Spontaneously Broken Symmetry In Bose-Einstein Condensates, Wj Mullin, F Laloe Feb 2011

Beyond Spontaneously Broken Symmetry In Bose-Einstein Condensates, Wj Mullin, F Laloe

William J. Mullin

Spontaneous symmetry breaking (SSB) for Bose-Einstein condensates cannot treat phase off-diagonal effects, and thus cannot explain Bell inequality violations. We describe another situation that is beyond a SSB treatment: an experiment where particles from two (possibly macroscopic) condensate sources are used for conjugate measurements of the relative phase and populations. Off-diagonal phase effects are characterized by a “quantum angle” and observed via “population oscillations,” signaling quantum interference of macroscopically distinct states.


Cooling By Flow Through Narrow Pores, Wj Mullin, N Kalechofsky Feb 2011

Cooling By Flow Through Narrow Pores, Wj Mullin, N Kalechofsky

William J. Mullin

We consider the possibility of cooling 3He atoms in dilute solutions with liquid 4He by “filtering out” the hot atoms through a screen of small holes or channels. The proposed method is somewhat analogous to that employed to evaporatively cool trapped gases, and the specific heat of the 3He-4He mixture makes it feasible to use in a device to refrigerate other samples. Three methods are considered: 1) Effusion through holes having diameters larger than a mean free path allowing atoms to pass through easily; 2) Particle waveguide-like motion (also effusive) using very narrow channels that greatly restrict the quantum states ...


Derivation Of Transverse Spin-Wave Dynamics From A Kinetic Equation In A Rotating Reference, Wj Mullin, Rj Ragan Feb 2011

Derivation Of Transverse Spin-Wave Dynamics From A Kinetic Equation In A Rotating Reference, Wj Mullin, Rj Ragan

William J. Mullin

In 1997 Fomin challenged the results of several theoretical groups who had predicted that there could be finite damping of spin-waves in the limit T -> 0. His method involved deriving a Lagrangian in a reference frame tied to the oscillating magnetization. He claimed to show that there was no diffusive damping (that is, of second order in wave vector q). We reopen this question by examining, under similar conditions, how a kinetic equation behaves in an equivalent reference frame. We arrive at Fomin's equations modified by inclusion of q2 damping of the spin-wave modes. Our result sharpens and perhaps ...


Permutation Cycles In The Bose-Einstein Condensation Of A Trapped Ideal Gas, Wj Mullin Feb 2011

Permutation Cycles In The Bose-Einstein Condensation Of A Trapped Ideal Gas, Wj Mullin

William J. Mullin

We consider Bose–Einstein condensation for non-interacting particles trapped in a harmonic potential by considering the length of permutation cycles arising from wave function symmetry. This approach had been considered previously by Matsubara and Feynman for a homogeneous gas in a box with periodic boundary conditions. For the ideal gas in a harmonic potential, one can treat the problem nearly exactly by analytical means. One clearly sees that the noncondensate is made up of permutation loops that are of length less-than-or-equals, slantN1/3, and that the phase transition consists of the sudden growth of longer permutation cycles. The condensate is ...


Quantum Statistics: Is There An Effective Fermion Repulsion Or Boson Attraction?, Wj Mullin, G Blaylock Feb 2011

Quantum Statistics: Is There An Effective Fermion Repulsion Or Boson Attraction?, Wj Mullin, G Blaylock

William J. Mullin

Physicists often claim that there is an effective repulsion between fermions, implied by the Pauli principle, and a corresponding effective attraction between bosons. We examine the origins and validity of such exchange force ideas and the areas where they are highly misleading. We propose that explanations of quantum statistics should avoid the idea of an effective force completely, and replace it with more appropriate physical insights, some of which are suggested here.


Analysis Of Certain Binary Collision Approximation Closures Of The Bbgky Hierarchy, Rf Snider, Wj Mullin, F Laloe Feb 2011

Analysis Of Certain Binary Collision Approximation Closures Of The Bbgky Hierarchy, Rf Snider, Wj Mullin, F Laloe

William J. Mullin

The closure of the BBGKY hierarchy to obtain the Boltzmann equation requires, in particular, restricting particle interactions to include only isolated binary collisions. Boercker and Dufty accomplish this by approximating the three-particle reduced density operator in a particular manner that favours correlation between two of the particles, while ignoring the correlation with the third. The tradition of most other closures has more closely followed Boltzmann's original thinking to completely neglect any reference to three-particle effects while assuming a generalized form of molecular chaos for the pair density operator. The two closures are compared in two ways: (a) by finding ...


Classical Phases And Quantum Angles In The Description Of Interfering Bose-Einstein Condensates, Wj Mullin, F Laloe Feb 2011

Classical Phases And Quantum Angles In The Description Of Interfering Bose-Einstein Condensates, Wj Mullin, F Laloe

William J. Mullin

The interference of two Bose-Einstein condensates, initially in Fock states, can be described in terms of their relative phase, treated as a random unknown variable. This phase can be understood either as emerging from the measurements or pre-existing to them; in the latter case, the originating states could be phase states with unknown phases, so an average over all their possible values is taken. Both points of view lead to a description of probabilities of results of experiments in terms of a phase angle, which plays the role of a classical variable. Nevertheless, in some situations, this description is not ...


Longitudinal Relaxation-Time For Dilute Quantum Gases, Wj Mullin, F Laloe, Mg Richards Feb 2011

Longitudinal Relaxation-Time For Dilute Quantum Gases, Wj Mullin, F Laloe, Mg Richards

William J. Mullin

We calculate the longitudinal relaxation timeT 1 for a polarized spin-1/2 Fermi gas, in zero magnetic field, for conditions of temperatureT and densityn such that Boltzmann statistics are valid. Our results show generally thatT 1 is independent of polarization of the gas. At highT, where the thermal wavelength lambda is small compared to the scattering lengtha, T 1 is proportionalT 1/2, while at lowT, such that lambda is greater thana, T 1 is proportional toT –1/2.T 1 thus has a minimum at some intermediate temperature confirming the numerical results of Shizgal. Physical arguments show that the ...


Path-Integral Monte Carlo And The Squeezed Trapped Bose-Einstein Gas, Jp Fernandez, Wj Mullin Feb 2011

Path-Integral Monte Carlo And The Squeezed Trapped Bose-Einstein Gas, Jp Fernandez, Wj Mullin

William J. Mullin

Bose-Einstein condensation has been experimentally found to take place in finite trapped systems when one of the confining frequencies is increased until the gas becomes effectively two-dimensional (2D). We confirm the plausibility of this result by performing path-integral Monte Carlo (PIMC) simulations of trapped Bose gases of increasing anisotropy and comparing them to the predictions of finite-temperature many-body theory. PIMC simulations provide an essentially exact description of these systems; they yield the density profile directly and provide two different estimates for the condensate fraction. For the ideal gas, we find that the PIMC column density of the squeezed gas corresponds ...


Kinetic-Equation For Dilute, Spin-Polarized Quantum-Systems, Jw Jeon, Wj Mullin Feb 2011

Kinetic-Equation For Dilute, Spin-Polarized Quantum-Systems, Jw Jeon, Wj Mullin

William J. Mullin

A kinetic equation, which includes the effects of degeneracy, is derived for dilute, polarized systems by the Green's function method of Kadanoff and Baym. When the Born approximation is used for the self-energy, the equation reduces to a result due to Silin. In the Boltzmann limit our result is equivalent to the equation of Lhuillier and Laloë, with the addition of a mean-field drift term analogous to that appearing in the Landau-Silin equation. Our kinetic equation is used to derive an expression for the transverse spin-diffusion relaxation time, τ>, for a Fermi system. In the Boltzmann and low-polarization limits ...


Multiple Spill Echoes Due To Anisotropic Spill Diffusion In He-3-He-4 Solutions, Rj Ragan, Wj Mullin Feb 2011

Multiple Spill Echoes Due To Anisotropic Spill Diffusion In He-3-He-4 Solutions, Rj Ragan, Wj Mullin

William J. Mullin

No abstract provided.


Some Equilibrium Properties Of Polarized, Dilute-Solutions Of H-3 In Superfluid He-4, P Hessling, Wj Mullin Feb 2011

Some Equilibrium Properties Of Polarized, Dilute-Solutions Of H-3 In Superfluid He-4, P Hessling, Wj Mullin

William J. Mullin

Formulas for of osmotic pressure and second sound velocity of a polarized system are derived and applied to polarized dilute solutions of3He in superfluid4He. Results are compared to experiment. Agreement is reasonable, but inferior to that obtained for transport properties reinforcing the claim of Meyerovich that the theory may have some conceptual difficulties.


Bose Condensation Of Idealized Spin-Polarized Atomic-Hydrogen In Equilibrium, Wj Mullin Feb 2011

Bose Condensation Of Idealized Spin-Polarized Atomic-Hydrogen In Equilibrium, Wj Mullin

William J. Mullin

A model of spin-polarized hydrogen (H↑) is treated in which interactions between atoms are neglected while the single-atom Zeeman and hyperfine interactions are treated exactly. These magnetic terms in the Hamiltonian are found to affect substantially the Bose-Einstein condensation and the various thermodynamic variables. Computations are discussed of the condensation temperature, condensate density, and specific heat in order to indicate how changes in magnetic field strength might be expected to affect future measurements on this quantum system.


Symmetry Constraints On The Spin Dynamics Of Polarised He-3, B Cowan, Wj Mullin, S Tehrani-Nasab Feb 2011

Symmetry Constraints On The Spin Dynamics Of Polarised He-3, B Cowan, Wj Mullin, S Tehrani-Nasab

William J. Mullin

The Leggett–Rice effect in liquid 3He was proposed on the basis of Fermi liquid interactions of the 3He quasiparticles. Consideration of the interparticle interactions in polarised gaseous 3He led, similarly, to spin rotation effects describable by a Leggett–Rice equation. In spin polarised solid 3He an analogous effect has been proposed from a consideration of the inter-nuclear exchange interaction. We show, in this paper, that spin rotation behaviour of the Leggett–Rice type in all these systems may be understood as a consequence of symmetry constraints.


Solution Of The Kinetic-Equation For Polarized Fermi Systems At All Temperatures, Jw Jeon, Wj Mullin Feb 2011

Solution Of The Kinetic-Equation For Polarized Fermi Systems At All Temperatures, Jw Jeon, Wj Mullin

William J. Mullin

We have solved the kinetic equation for a dilute, polarized Fermi system for a range of temperatures from the degenerate limit to the Boltzmann case. The solution is possible because we have been able to reduce the collision integral to two-fold form. We calculate the spin diffusion constant and find the expected results for the degenerate and Boltzmann limits, improved results for the high polarization regime in which one spin species is degenerate and one Boltzmann, and values for all intermediate temperatures as well. Because of a relation between the collision time and the “spin rotation quality parameter”, µ, we ...


Exact Transport-Properties Of Degenerate, Weakly Interacting, And Spin-Polarized Fermions, Wj Mullin, K Miyake Feb 2011

Exact Transport-Properties Of Degenerate, Weakly Interacting, And Spin-Polarized Fermions, Wj Mullin, K Miyake

William J. Mullin

Exact results for the transport coefficients of a highly degenerate spin-polarized Fermi system are presented. The case of weakly interacting particles, such as dilute3He in4He or D darr, is treated. The results are compared to the variational treatment and corrections as large as 8% are found. Detailed behavior of the polarization of an ideal Fermi gas as a function of temperature and magnetic field is discussed as a model for dilute3He in4He. Limits of applicability of the formulas are given. We find that at appropriate fields and temperatures, the two spin species may be considered to be a mixture of ...


Einstein-Podolsky-Rosen Argument And Bell Inequalities For Bose-Einstein Spin Condensates, F Laloe, Wj Mullin Feb 2011

Einstein-Podolsky-Rosen Argument And Bell Inequalities For Bose-Einstein Spin Condensates, F Laloe, Wj Mullin

William J. Mullin

We discuss the properties of two Bose-Einstein condensates in different spin states, represented quantum mechanically by a double Fock state. Individual measurements of the spins of the particles are performed in transverse directions (perpendicular to the spin quantization axis), giving access to the relative phase of the two macroscopically occupied states. Before the first spin measurement, the phase is completely undetermined; after a few measurements, a more and more precise knowledge of its value emerges under the effect of the quantum measurement process. This naturally leads to the usual notion of a quasiclassical phase (Anderson phase) and to an interesting ...


Quantum-Monte-Carlo Calculations For Bosons In A Two-Dimensional Harmonic Trap, Stefan Heinrichs, William J. Mullin Feb 2011

Quantum-Monte-Carlo Calculations For Bosons In A Two-Dimensional Harmonic Trap, Stefan Heinrichs, William J. Mullin

William J. Mullin

Path-Integral-Monte-Carlo simulation has been used to calculate the properties of a two-dimensional (2D) interacting Bose system. The bosons interact with hard-core potentials and are confined to a harmonic trap. Results for the density profiles, the condensate fraction, and the superfluid density are presented. By comparing with the ideal gas we easily observe the effects of finite size and the depletion of the condensate because of interactions. The system is known to have no phase transition to a Bose-Einstein condensation in 2D, but the finite system shows that a significant fraction of the particles are in the lowest state at low ...


Epr Argument And Bell Inequalities For Bose-Einstein Spin Condensates, Franck Laloe, Wj Mullin Feb 2011

Epr Argument And Bell Inequalities For Bose-Einstein Spin Condensates, Franck Laloe, Wj Mullin

William J. Mullin

We discuss the properties of two Bose-Einstein condensates in different spin states, represented quantum mechanically by a double Fock state. Individual measurements of the spins of the particles are performed in transverse directions (perpendicular to the spin quantization axis), giving access to the relative phase of the two macroscopically occupied states. Before the first spin measurement, the phase is completely undetermined; after a few measurements, a more and more precise knowledge of its value emerges under the effect of the quantum measurement process. This naturally leads to the usual notion of a quasiclassical phase (Anderson phase) and to an interesting ...


Evolution Of Additional (Hidden) Quantum Variables In The Interference Of Bose-Einstein Condensates, Wj Mullin, R Krotkov, F Laloe Feb 2011

Evolution Of Additional (Hidden) Quantum Variables In The Interference Of Bose-Einstein Condensates, Wj Mullin, R Krotkov, F Laloe

William J. Mullin

Additional variables (also often called “hidden variables”) are sometimes added to standard quantum mechanics in order to remove its indeterminism or “incompleteness” and to make the measurement process look more classical. Here we discuss a case in which an additional variable arises almost spontaneously from the quantum formalism: the emergence of a relative phase between two highly populated Fock-state Bose-Einstein condensates. The model simulated here involves the interference of two Bose condensates, one with all up spins and the other with down spins, along a z axis. With the clouds overlapping, we consider the results of measuring spins in a ...


Flow Of Polarized Fermi Gases Through Narrow Channels, Wj Mullin Feb 2011

Flow Of Polarized Fermi Gases Through Narrow Channels, Wj Mullin

William J. Mullin

The flow of a polarized Fermi gas through channels from one cell to another can be used to study its transport properties. If the mean free path λ in the gas is smaller than the radius r of a channel, the time constant for the filling of an empty chamber can yield the viscosity of the gas in both the Boltzmann and degenerate cases. If λ>r and the gas is degenerate, a novel effect is predicted: Because the Fermi velocities of the two spin species are different, the polarization in the second cell will initially have a value greater ...


A Leggett-Rice Effect In Solid He-3-Spin Rotation Induced By Exchange, B Cowan, Wj Mullin, S Tehraninasab Feb 2011

A Leggett-Rice Effect In Solid He-3-Spin Rotation Induced By Exchange, B Cowan, Wj Mullin, S Tehraninasab

William J. Mullin

In solid3He the internuclear exchange interaction may be interpreted as a molecular field, as in the Weiss theory of magnetism. In an applied magnetic field the magnetic moment precesses about the total magnetic field, to which the molecular field contributes. As Leggett showed for liquid helium in the Fermi liquid region, this leads to a modification of the time evolution of the magnetisation; it is no longer purely diffusive. In solid3He at low polarisation there is conventional spin diffusion; at high polarisations the evolution is in the form of spin waves. We show that the intermediate behaviour may be expressed ...


The Two-Dimensional Bose-Einstein Condensate, Jp Fernandez, Wj Mullin Feb 2011

The Two-Dimensional Bose-Einstein Condensate, Jp Fernandez, Wj Mullin

William J. Mullin

We study the Hartree–Fock–Bogoliubov mean-field theory as applied to a two-dimensional finite trapped Bose gas at low temperatures and find that, in the Hartree–Fock approximation, the system can be described either with or without the presence of a condensate; this is true in the thermodynamic limit as well. Of the two solutions, the one that includes a condensate has a lower free energy at all temperatures. However, the Hartree–Fock scheme neglects the presence of phonons within the system, and when we allow for the possibility of phonons we are unable to find condensed solutions; the uncondensed ...