137 research outputs found
Vortices and turbulence in trapped atomic condensates
After over a decade of experiments generating and studying the physics of
quantized vortices in atomic gas Bose-Einstein condensates, research is
beginning to focus on the roles of vortices in quantum turbulence, as well as
other measures of quantum turbulence in atomic condensates. Such research
directions have the potential to uncover new insights into quantum turbulence,
vortices and superfluidity, and also explore the similarities and differences
between quantum and classical turbulence in entirely new settings. Here we
present a critical assessment of theoretical and experimental studies in this
emerging field of quantum turbulence in atomic condensates
Análogo mecânico para a condutividade elétrica dos metais : efeitos da temperatura
Electrical conductivity is one of the most important concepts within aspects of modern physics with a great extension to materials science. It is responsible for most applications of metallic and semiconductor materials. The understanding of microscopic models that reproduce certain characteristics is an important step towards the understanding of materials. In this work we continue to use a system that constitutes a mechanical analogue to understand how the limitations of electrical conductivity of metals occur. Using this model we investigated the effect of temperature on conductivity. The model presented here is quite instructive and lends itself very well to demonstrations in the classroom or even for carrying out laboratory practices in undergraduate courses or teaching practices in Physics in High School
Simple analysis of off-axis solenoid fields using the scalar magnetostatic potential: application to a Zeeman-slower for cold atoms
In a region free of currents, magnetostatics can be described by the Laplace
equation of a scalar magnetic potential, and one can apply the same methods
commonly used in electrostatics. Here we show how to calculate the general
vector field inside a real (finite) solenoid, using only the magnitude of the
field along the symmetry axis. Our method does not require integration or
knowledge of the current distribution, and is presented through practical
examples, including a non-uniform finite solenoid used to produce cold atomic
beams via laser cooling. These examples allow educators to discuss the
non-trivial calculation of fields off-axis using concepts familiar to most
students, while offering the opportunity to introduce important advancements of
current modern research.Comment: 6 pages. Accepted in the American Journal of Physic
Bose-Einstein Condensation on Curved Manifolds
Here we describe a weakly interacting Bose gas on a curved manifold, which is
embedded in the three-dimensional Euclidean space.~To this end we start by
considering a harmonic trap in the normal direction of the manifold, which
confines the three-dimensional Bose gas in the vicinity of its
surface.~Following the notion of dimensional reduction as outlined in
[L.~Salasnich et al., Phys.~Rev.~A {\bf 65}, 043614 (2002)], we assume a large
enough trap frequency so that the normal degree of freedom of the condensate
wave function can be approximately integrated out. In this way we obtain an
effective condensate wave function on the quasi-two-dimensional surface of the
curved manifold, where the thickness of the cloud is determined
self-consistently. For the particular case when the manifold is a sphere, our
equilibrium results show how the chemical potential and the thickness of the
cloud increase with the interaction strength.~Furthermore, we determine within
a linear stability analysis the low-lying collective excitations together with
their eigenfrequencies, which turn out to reveal an instability for attractive
interactions.Comment: 33 pages, 6 figure
Intra-scales energy transfer during the evolution of turbulence in a trapped Bose-Einstein condensate
In turbulence phenomena, including the quantum turbulence in superfluids, an
energy flux flows from large to small length scales, composing a cascade of
energy. A universal characteristic of turbulent flows is the existence of a
range of scales where the energy flux is scale-invariant: this interval of
scales is often referred to as inertial region. This property is fundamental
as, for instance, in turbulence of classical fluids it characterizes the
behavior of statistical features such as spectra and structure functions. Here
we show that also in decaying quantum turbulence generated in trapped
Bose-Einstein condensates (BECs), intervals of momentum space where the energy
flux is constant can be identified. Indeed, we present a procedure to measure
the energy flux using both the energy spectrum and the continuity equation. A
range of scales where the flux is constant is then determined employing two
distinct protocols and in the same range, the momentum distribution measured is
consistent with previous work. The successful identification of a region with
constant flux in turbulent BECs is a manifestation of the universal character
of turbulence in these quantum systems. These measurements pave the way for
studies of energy conservation and dissipation in trapped atomic superfluids,
and also analogies with the related processes that take place in ordinary
fluids.Comment: 7 pages, 5 figure
Entropy of a Turbulent Bose-Einstein Condensate
Quantum turbulence deals with the phenomenon of turbulence in quantum fluids,
such as superfluid helium and trapped Bose-Einstein condensates (BECs).
Although much progress has been made in understanding quantum turbulence,
several fundamental questions remain to be answered. In this work, we
investigated the entropy of a trapped BEC in several regimes, including
equilibrium, small excitations, the onset of turbulence, and a turbulent state.
We considered the time evolution when the system is perturbed and let to evolve
after the external excitation is turned off. We derived an expression for the
entropy consistent with the accessible experimental data, that is, using the
assumption that the momentum distribution is well-known. We related the
excitation amplitude to different stages of the perturbed system, and we found
distinct features of the entropy in each of them. In particular, we observed a
sudden increase in the entropy following the establishment of a particle
cascade. We argue that entropy and related quantities can be used to
investigate and characterize quantum turbulence.Comment: 14 pages, 5 figure
- …