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Full-Text Articles in Physics
Bose-Einstein Condensation In A Harmonic Potential, Wj Mullin
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 it vanishes …
Classical Phases And Quantum Angles In The Description Of Interfering Bose-Einstein Condensates, Wj Mullin, F Laloe
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 …
Quantum-Monte-Carlo Calculations For Bosons In A Two-Dimensional Harmonic Trap, Stefan Heinrichs, William J. Mullin
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
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
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 …
The Two-Dimensional Bose-Einstein Condensate, Jp Fernandez, Wj Mullin
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 solutions, on the other …
Quantum-Monte-Carlo Calculations For Bosons In A Two-Dimensional Harmonic Trap, S Heinrichs, Wj Mullin
Quantum-Monte-Carlo Calculations For Bosons In A Two-Dimensional Harmonic Trap, S Heinrichs, Wj 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 …
Giant Viscosity Enhancement In A Spin-Polarized Fermi Liquid, H Akimoto, Js Xia, D Candela, Wj Mullin, Ed Adams, Ns Sullivan
Giant Viscosity Enhancement In A Spin-Polarized Fermi Liquid, H Akimoto, Js Xia, D Candela, Wj Mullin, Ed Adams, Ns Sullivan
William J. Mullin
The viscosity is measured for a Fermi liquid, a dilute 3He-4He mixture, under extremely high magnetic field/temperature conditions (B≤14.8 T, T≥1.5 mK). The spin-splitting energy μB is substantially greater than the Fermi energy kBTF; as a consequence the polarization tends to unity and s-wave quasiparticle scattering is suppressed for T≪TF. Using a novel composite vibrating-wire viscometer an enhancement of the viscosity is observed by a factor of more than 500 over its low-field value. Good agreement is found between the measured viscosity and theoretical predictions based upon a t-matrix formalism.
Spin Diffusion In Trapped Gases: Anisotropy In Dipole And Quadrupole Modes, Wj Mullin, Rj Ragan
Spin Diffusion In Trapped Gases: Anisotropy In Dipole And Quadrupole Modes, Wj Mullin, Rj Ragan
William J. Mullin
Recent experiments in a mixture of two hyperfine states of trapped Bose gases show behavior analogous to a spin-1/2 system, including transverse spin waves and other familiar Leggett-Rice-type effects. We have derived the kinetic equations applicable to these systems, including the spin dependence of interparticle interactions in the collision integral, and have solved for spin-wave frequencies and longitudinal and transverse diffusion constants in the Boltzmann limit. We find that, while the transverse and longitudinal collision times for trapped Fermi gases are identical, the Bose gas shows unusual diffusion anisotropy in both dipole and quadrupole modes. Moreover, the lack of spin …
Interferometry With Independent Bose-Einstein Condensates: Parity As An Epr/Bell Quantum Variable, F Laloe, Wj Mullin
Interferometry With Independent Bose-Einstein Condensates: Parity As An Epr/Bell Quantum Variable, F Laloe, Wj Mullin
William J. Mullin
When independent Bose-Einstein condensates (BEC), described quantum mechanically by Fock (number) states, are sent into interferometers, the measurement of the output port at which the particles are detected provides a binary measurement, with two possible results ±1. With two interferometers and two BEC’s, the parity (product of all results obtained at each interferometer) has all the features of an Einstein-Podolsky-Rosen quantity, with perfect correlations predicted by quantum mechanics when the settings (phase shifts of the interferometers) are the same. When they are different, significant violations of Bell inequalities are obtained. These violations do not tend to zero when the number …
Quantum-Limited Mass Flow Of Liquid He-3, G Lambert, G Gervais, Wj Mullin
Quantum-Limited Mass Flow Of Liquid He-3, G Lambert, G Gervais, Wj Mullin
William J. Mullin
We consider theoretically the possibility of observing unusual quantum fluid behavior in liquid 3He and solutions of 3He in 4He systems confined to nanochannels. In the case of pure ballistic flow at very low temperature the conductance will be quantized in units of 2m2/h. We show that these steps should be sensitive to increases in temperature. We also use a random scattering matrix simulation to study flow with diffusive wall scattering. Universal conductance fluctuations analogous to those seen in electron systems should then be observable. Finally we consider the possibility of crossover to a one-dimensional system at sufficiently low temperature, …
Landau Damping Of Spin Waves In Trapped Boltzmann Gases, Rj Ragan, Wj Mullin, Eb Wiita
Landau Damping Of Spin Waves In Trapped Boltzmann Gases, Rj Ragan, Wj Mullin, Eb Wiita
William J. Mullin
A semiclassical method is used to study Landau damping of transverse pseudo-spin waves in harmonically trapped ultracold gases in the collisionless Boltzmann limit. In this approach, the time evolution of a spin is calculated numerically as it travels in a classical orbit through a spatially dependent mean field. This method reproduces the Landau damping results for spin-waves in unbounded systems obtained with a dielectric formalism. In trapped systems, the simulations indicate that Landan damping occurs for a given spin-wave mode because of resonant phase space trajectories in which spins are "kicked out" of the mode (in spin space). A perturbative …
Interference Of Bose-Einstein Condensates: Quantum Nonlocal Effects, Wj Mullin, F Laloe
Interference Of Bose-Einstein Condensates: Quantum Nonlocal Effects, Wj Mullin, F Laloe
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 …
Anisotropic Spin Diffusion In Trapped Boltzmann Gases, Wj Mullin, Rj Ragan
Anisotropic Spin Diffusion In Trapped Boltzmann Gases, Wj Mullin, Rj Ragan
William J. Mullin
Recent experiments in a mixture of two hyperfine states of trapped Bose gases show behavior analogous to a spin-1/2 system, including transverse spin waves and other familiar Leggett-Rice-type effects. We have derived the kinetic equations applicable to these systems, including the spin dependence of interparticle interactions in the collision integral, and have solved for spin-wave frequencies and longitudinal and transverse diffusion constants in the Boltzmann limit. We find that, while the transverse and longitudinal collision times for trapped Fermi gases are identical, the Bose gas shows diffusion anisotropy. Moreover, the lack of spin isotropy in the interactions leads to the …
Absence Of Fragmentation In Two-Dimensional Bose-Einstein Condensation, Jp Fernandez, Wj Mullin
Absence Of Fragmentation In Two-Dimensional Bose-Einstein Condensation, Jp Fernandez, Wj Mullin
William J. Mullin
We investigate the possibility that the BEC-like phenomena recently detected on two-dimensional finite trapped systems consist of fragmented condensates. We derive and diagonalize the one-body density matrix of a two-dimensional isotropically trapped Bose gas at finite temperature. For the ideal gas, the procedure reproduces the exact harmonic-oscillator eigenfunctions and the Bose distribution. We use a new collocation-minimization method to study the interacting gas in the Hartree-Fock approximation and obtain a ground-state wavefunction and condensate fraction consistent with those obtained by other methods. The populations of the next few eigenstates increase at the expense of the ground state but continue to …
Theory Of Cooling By Flow Through Narrow Pores, Wj Mullin, N Kalechofsky
Theory Of Cooling By Flow Through Narrow Pores, Wj Mullin, N Kalechofsky
William J. Mullin
We consider the possibility of adding a stage to a dilution refrigerator to provide additional cooling by “filtering out” hot atoms. Three methods are considered: (1) effusion, where holes having diameters larger than a mean-free path allow atoms to pass through easily; (2) particle waveguidelike motion using very narrow channels that greatly restrict the quantum states of the atoms in a channel; (3) wall-limited diffusion through channels, in which the wall scattering is disordered so that local density equilibrium is established in a channel. We assume that channel dimensions are smaller than the mean-free path for atom-atom interactions. The particle …
New Evidence For Zero-Temperature Relaxation In A Spin-Polarized Fermi Liquid, H Akimoto, D Candela, Js Xia, Wj Mullin, Ed Adams, Ns Sullivan
New Evidence For Zero-Temperature Relaxation In A Spin-Polarized Fermi Liquid, H Akimoto, D Candela, Js Xia, Wj Mullin, Ed Adams, Ns Sullivan
William J. Mullin
Spin-echo experiments are reported for 3He-4He solutions under extremely high B/T conditions, B=14.75 T and T≥1.73 mK. The 3He concentration x3 was adjusted close to the value xc≈3.8% at which the spin-rotation parameter μM0 vanishes. In this way the transverse and longitudinal spin-diffusion coefficients D⊥,D∥ were measured while keeping |μM0|<1. It is found that the temperature dependence of D⊥ deviates strongly from 1/T2, with anisotropy temperature Ta=4.26-0.44+0.18 mK. This value is close to the theoretical prediction for dilute solutions and suggests that spin current relaxation remains finite as the temperature tends to zero.
The Loop-Gas Approach To Bose-Einstein Condensation For Trapped Particles, Wj Mullin
The Loop-Gas Approach To Bose-Einstein Condensation For Trapped Particles, Wj Mullin
William J. Mullin
We examine Bose–Einstein condensation (BEC) for particles trapped in a harmonic potential by considering it as a transition in the length of permutation cycles that arise from wave-function symmetry. This “loop-gas” approach was originally developed by Feynman in his path-integral study of BEC for a homogeneous gas in a box. For the harmonic oscillator potential it is possible to treat the ideal gas exactly so that one can easily see how standard approximations become more accurate in the thermodynamic limit (TDL). One clearly sees that the condensate is made up of very long permutation loops whose length fluctuates ever more …