78 research outputs found
Spin dynamics and structure formation in a spin-1 condensate in a magnetic field
We study the dynamics of a trapped spin-1 condensate in a magnetic field. First, we analyze the homogeneous system, for which the dynamics can be understood in terms of orbits in phase space. We analytically solve for the dynamical evolution of the populations of the various Zeeman components of the homogeneous system. This result is then applied via a local-density approximation to trapped quasi-one-dimensional condensates. Our analysis of the trapped system in a magnetic field shows that both the mean-field and Zeeman regimes are simultaneously realized, and we argue that the border between these two regions is where spin domains and phase defects are generated. We propose a method to experimentally tune the position of this border
Spectral statistics of molecular resonances in erbium isotopes: How chaotic are they?
We perform a comprehensive analysis of the spectral statistics of the
molecular resonances in Er and Er observed in recent ultracold
collision experiments [Frisch et al., Nature {\bf 507}, 475 (2014)] with the
aim of determining the chaoticity of this system. We calculate different
independent statistical properties to check their degree of agreement with
random matrix theory (RMT), and analyze if they are consistent with the
possibility of having missing resonances. The analysis of the short-range
fluctuations as a function of the magnetic field points to a steady increase of
chaoticity until G. The repulsion parameter decreases for higher
magnetic fields, an effect that can be interpreted as due to missing
resonances. The analysis of long-range fluctuations allows us to be more
quantitative and estimate a fraction of missing levels. Finally, a
study of the distribution of resonance widths provides additional evidence
supporting missing resonances of small width compared with the experimental
magnetic field resolution. We conclude that further measurements with increased
resolution will be necessary to give a final answer to the problem of missing
resonances and the agreement with RMT.Comment: 9 pages, 6 figure
Density functional study of two-dimensional He-4 clusters
Binding energies and density profiles of two-dimensional systems of liquid
He-4 with different geometries are studied by means of a zero-range density
functional adjusted to reproduce the line tension obtained in a previous
diffusion Monte Carlo calculation (lambda_{DMC}=0.121 K/A). It is shown that
this density functional provides accurate results for the binding energy of
large clusters with a reasonable computational effort.Comment: RevTeX4, 11 pages + 2 tables + 6 figure
Spin mixing in colliding spinor condensates: formation of an effective barrier
The dynamics of F=1 spinor condensates initially prepared in a double-well
potential is studied in the mean field approach. It is shown that a small seed
of atoms on a system with initially well separated m=1 and m=-1
condensates has a dramatic effect on their mixing dynamics, acting as an
effective barrier for a remarkably long time. We show that this effect is due
to the spinor character of the system, and provides an observable example of
the interplay between the internal spin dynamics and the macroscopic evolution
of the magnetization in a spinor Bose-Einstein condensate.Comment: Accepted for publication at the Europhysics Letter
Predicting spinor condensate dynamics from simple principles
We study the spin dynamics of quasi-one-dimensional F=1 condensates both at
zero and finite temperatures for arbitrary initial spin configurations. The
rich dynamical evolution exhibited by these non-linear systems is explained by
surprisingly simple principles: minimization of energy at zero temperature, and
maximization of entropy at high temperature. Our analytical results for the
homogeneous case are corroborated by numerical simulations for confined
condensates in a wide variety of initial conditions. These predictions compare
qualitatively well with recent experimental observations and can, therefore,
serve as a guidance for on-going experiments.Comment: 4 pages, 2 figures. v3: matches version appeared in PR
Fluctuations of work in realistic equilibrium states of quantum systems with conserved quantities
The out-of-equilibrium dynamics of quantum systems is one of the most
fascinating problems in physics, with outstanding open questions on issues such
as relaxation to equilibrium. An area of particular interest concerns few-body
systems, where quantum and thermal fluctuations are expected to be especially
relevant. In this contribution, we present numerical results demonstrating the
impact of conserved quantities (or 'charges') in the outcomes of
out-of-equilibrium measurements starting from realistic equilibrium states on a
few-body system implementing the Dicke model.Comment: 12 pages, 1 fig. Contribution to Proceedings of the 24th European
Conference on Few-Body Problems in Physics (EFB24). Matches journal version
published under CC BY 4.
Temperature-independent quantum logic for molecular spectroscopy
We propose a fast and non-destructive spectroscopic method for single
molecular ions that implements quantum logic schemes between an atomic ion and
the molecular ion of interest. Our proposal relies on a hybrid coherent
manipulation of the two-ion system, using optical or magnetic forces depending
on the types of molecular levels to be addressed (Zeeman, rotational,
vibrational or electronic degrees of freedom). The method is especially suited
for the non-destructive precision spectroscopy of single molecular ions, and
sets a starting point for new hybrid quantum computation schemes that combine
molecular and atomic ions, covering the measurement and entangling steps.Comment: v3. Substantially enlarged manuscript with details of derivations and
calculations in two appendices. To appear in PR
Topological phase transitions between chiral and helical spin textures in a lattice with spin-orbit coupling and a magnetic field
We consider the combined effects of large spin-orbit couplings and a
perpendicular magnetic field in a 2D honeycomb fermionic lattice. This system
provides an elegant setup to generate versatile spin textures propagating along
the edge of a sample. The spin-orbit coupling is shown to induce topological
phase transitions between a helical quantum spin Hall phase and a chiral
spin-imbalanced quantum Hall state. Besides, we find that the spin orientation
of a single topological edge state can be tuned by a Rashba spin-orbit
coupling, opening an interesting route towards quantum spin manipulation. We
discuss the possible realization of our results using cold atoms trapped in
optical lattices, where large synthetic magnetic fields and spin-orbit
couplings can be engineered and finely tuned. In particular, this system would
lead to the observation of a time-reversal-symmetry-broken quantum spin Hall
phase.Comment: 8 pages, 3 figures, Accepted in Europhys. Lett. (Dec 2011
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