234 research outputs found
A primer on quantum fluids
This book introduces the theoretical description and properties of quantum
fluids. The focus is on gaseous atomic Bose-Einstein condensates and, to a
minor extent, superfluid helium, but the underlying concepts are relevant to
other forms of quantum fluids such as polariton and photonic condensates. The
book is pitched at the level of advanced undergraduates and early postgraduate
students, aiming to provide the reader with the knowledge and skills to develop
their own research project on quantum fluids. Indeed, the content for this book
grew from introductory notes provided to our own research students. It is
assumed that the reader has prior knowledge of undergraduate mathematics and/or
physics; otherwise, the concepts are introduced from scratch, often with
references for directed further reading.Comment: 132 pages. Published as SpringerBriefs in Physics book. Typos
corrected in this versio
Vortex nucleation by collapsing bubbles in Bose-Einstein condensates
The nucleation of vortex rings accompanies the collapse of ultrasound bubbles
in superfluids. Using the Gross-Pitaevskii equation for a uniform condensate we
elucidate the various stages of the collapse of a stationary spherically
symmetric bubble and establish conditions necessary for vortex nucleation. The
minimum radius of the stationary bubble, whose collapse leads to vortex
nucleation, was found to be about 28 healing lengths. The time after which the
nucleation becomes possible is determined as a function of bubble's radius. We
show that vortex nucleation takes place in moving bubbles of even smaller
radius if the motion made them sufficiently oblate.Comment: 4 pages, 5 figure
Ballistic propagation of thermal excitations near a vortex in superfluid He3-B
Andreev scattering of thermal excitations is a powerful tool for studying
quantized vortices and turbulence in superfluid He3-B at very low temperatures.
We write Hamilton's equations for a quasiparticle in the presence of a vortex
line, determine its trajectory, and find under wich conditions it is Andreev
reflected. To make contact with experiments, we generalize our results to the
Onsager vortex gas, and find values of the intervortex spacing in agreement
with less rigorous estimates
Quasiclassical and ultraquantum decay of superfluid turbulence
This letter addresses the question which, after a decade-long discussion,
still remains open: what is the nature of the ultraquantum regime of decay of
quantum turbulence? The model developed in this work reproduces both the
ultraquantum and the quasiclassical decay regimes and explains their
hydrodynamical natures. In the case where turbulence is generated by forcing at
some intermediate lengthscale, e.g. by the beam of vortex rings in the
experiment of Walmsley and Golov [Phys. Rev. Lett. {\bf 100}, 245301 (2008)],
we explained the mechanisms of generation of both ultraquantum and
quasiclassical regimes. We also found that the anisotropy of the beam is
important for generating the large scale motion associated with the
quasiclassical regime
- …