scholarly journals Snell's Law for a vortex dipole in a Bose-Einstein condensate

2019 ◽  
Vol 6 (3) ◽  
Author(s):  
Michael MacCormick Cawte ◽  
Xiaoquan Yu ◽  
Brian P. Anderson ◽  
Ashton Bradley
Keyword(s):  
Total Internal Reflection ◽  
Finite Size ◽  
Einstein Condensate ◽  
Quantum Vortex ◽  
Bose Einstein Condensate ◽  
Vortex Dipole ◽  
Wide Range ◽  
Snell’S Law ◽  
Snell's Law ◽  
Bose Einstein

A quantum vortex dipole, comprised of a closely bound pair of vortices of equal strength with opposite circulation, is a spatially localized travelling excitation of a planar superfluid that carries linear momentum, suggesting a possible analogy with ray optics. We investigate numerically and analytically the motion of a quantum vortex dipole incident upon a step-change in the background superfluid density of an otherwise uniform two-dimensional Bose-Einstein condensate. Due to the conservation of fluid momentum and energy, the incident and refracted angles of the dipole satisfy a relation analogous to Snell’s law, when crossing the interface between regions of different density. The predictions of the analogue Snell’s law relation are confirmed for a wide range of incident angles by systematic numerical simulations of the Gross-Piteavskii equation. Near the critical angle for total internal reflection, we identify a regime of anomalous Snell’s law behaviour where the finite size of the dipole causes transient capture by the interface. Remarkably, despite the extra complexity of the interface interaction, the incoming and outgoing dipole paths obey Snell’s law.

scholarly journals A degenerate Fermi gas of polar molecules

Science ◽  
2019 ◽  
Vol 363 (6429) ◽  
pp. 853-856 ◽  
Author(s):  
Luigi De Marco ◽  
Giacomo Valtolina ◽  
Kyle Matsuda ◽  
William G. Tobias ◽  
Jacob P. Covey ◽  
...  
Keyword(s):  
Fermi Gas ◽  
Einstein Condensate ◽  
Polar Molecules ◽  
Ultracold Molecules ◽  
Experimental Realization ◽  
Bose Einstein Condensate ◽  
Degenerate Fermi Gas ◽  
Fermi Temperature ◽  
Wide Range ◽  
Bose Einstein

Experimental realization of a quantum degenerate gas of molecules would provide access to a wide range of phenomena in molecular and quantum sciences. However, the very complexity that makes ultracold molecules so enticing has made reaching degeneracy an outstanding experimental challenge over the past decade. We now report the production of a degenerate Fermi gas of ultracold polar molecules of potassium-rubidium. Through coherent adiabatic association in a deeply degenerate mixture of a rubidium Bose-Einstein condensate and a potassium Fermi gas, we produce molecules at temperatures below 0.3 times the Fermi temperature. We explore the properties of this reactive gas and demonstrate how degeneracy suppresses chemical reactions, making a long-lived degenerate gas of polar molecules a reality.

scholarly journals Homogeneous one-dimensional Bose–Einstein condensate in the Bogoliubov’s regime

2016 ◽  
Vol 30 (22) ◽  
pp. 1650307 ◽  
Author(s):  
Elías Castellanos
Keyword(s):  
Ground State ◽  
Size Effects ◽  
Finite Size ◽  
Einstein Condensate ◽  
Finite Size Effects ◽  
One Dimensional ◽  
Bose Einstein Condensate ◽  
Ground State Properties ◽  
Low Dimensional ◽  
Bose Einstein

We analyze the corrections caused by finite size effects upon the ground state properties of a homogeneous one-dimensional (1D) Bose–Einstein condensate. We assume from the very beginning that the Bogoliubov’s formalism is valid and consequently, we show that in order to obtain a well-defined ground state properties, finite size effects of the system must be taken into account. Indeed, the formalism described in the present paper allows to recover the usual properties related to the ground state of a homogeneous 1D Bose–Einstein condensate but corrected by finite size effects of the system. Finally, this scenario allows us to analyze the sensitivity of the system when the Bogoliubov’s regime is valid and when finite size effects are present. These facts open the possibility to apply these ideas to more realistic scenarios, e.g. low-dimensional trapped Bose–Einstein condensates.

scholarly journals Casimir Force between Two Vortices in a Turbulent Bose–Einstein Condensate

Atoms ◽  
2020 ◽  
Vol 8 (4) ◽  
pp. 77
Author(s):  
José Tito Mendonça ◽  
Hugo Terças ◽  
João D. Rodrigues ◽  
Arnaldo Gammal
Keyword(s):  
Casimir Force ◽  
Occupation Number ◽  
Finite Size ◽  
Condensed Medium ◽  
Einstein Condensate ◽  
Density Fluctuations ◽  
Pitaevskii Equation ◽  
Phonon Modes ◽  
Bose Einstein Condensate ◽  
Bose Einstein

We consider the Casimir force between two vortices due to the presence of density fluctuations induced by turbulent modes in a Bose–Einstein condensate. We discuss the cases of unbounded and finite condensates. Turbulence is described as a superposition of elementary excitations (phonons or BdG modes) in the medium. Expressions for the Casimir force between two identical vortex lines are derived, assuming that the vortices behave as point particles. Our analytical model of the Casimir force is confirmed by numerical simulations of the Gross–Pitaevskii equation, where the finite size of the vortices is retained. Our results are valid in the mean-field description of the turbulent medium. However, the Casimir force due to quantum fluctuations can also be estimated, assuming the particular case where the occupation number of the phonon modes in the condensed medium is reduced to zero and only zero-point fluctuations remain.

scholarly journals Slowly rotating Bose–Einstein condensate compared with the rotation curves of 12 dwarf galaxies

2020 ◽  
Vol 633 ◽  
pp. A75
Author(s):  
E. Kun ◽  
Z. Keresztes ◽  
L. Á. Gergely
Keyword(s):  
Dark Matter ◽  
Angular Velocity ◽  
Surface Brightness ◽  
Rotation Curve ◽  
Dwarf Galaxies ◽  
Finite Size ◽  
Einstein Condensate ◽  
Bose Einstein Condensate ◽  
Bose Einstein ◽  
Model Fits

Context. The high plateaus of the rotation curves of spiral galaxies suggest either that there is a dark component or that the Newtonian gravity requires modifications on galactic scales to explain the observations. We assemble a database of 12 dwarf galaxies, for which optical (R-band) and near-infrared (3.6 μm) surface brightness density together with spectroscopic rotation curve data are available, in order to test the slowly rotating Bose–Einstein condensate (BEC) dark matter model. Aims. We aim to establish the angular velocity range compatible with observations, bounded from above by the requirement of finite-size halos, to check the model fits with the dataset, and the universality of the BEC halo parameter ℛ. Methods. We constructed the spatial luminosity density of the stellar component of the dwarf galaxies based on their 3.6 μm and R-band surface brightness profiles, assuming an axisymmetric baryonic mass distribution with arbitrary axis ratio. We built up the gaseous component of the mass by employing an inside-truncated disk model. We fitted a baryonic plus dark matter combined model, parametrized by the M/L ratios of the baryonic components and parameters of the slowly rotating BEC (the central density ρc, size of the BEC halo ℛ in the static limit, angular velocity ω) to the rotation curve data. Results. The 3.6 μm surface brightness of six galaxies indicates the presence of a bulge and a disk component. The shape of the 3.6 μm and R-band spatial mass density profiles being similar is consistent with the stellar mass of the galaxies emerging wavelength-independent. The slowly rotating BEC model fits the rotation curve of 11 galaxies out of 12 within the 1σ significance level, with the average of ℛ as 7.51 kpc and standard deviation of 2.96 kpc. This represents an improvement over the static BEC model fits, also discussed. For the 11 best-fitting galaxies the angular velocities allowing for a finite-size slowly rotating BEC halo are less then 2.2 × 10−16 s−1.For a scattering length of the BEC particle of a ≈ 106 fm, as allowed by terrestrial laboratory experiments, the mass of the BEC particle is slightly better constrained than in the static case as m ∈ [1.26 × 10−17 ÷ 3.08 × 10−17] (eV c−2).

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