10 research outputs found
Competition between Bose Einstein Condensation and spin dynamics
We study the impact of spin-exchange collisions on the dynamics of
Bose-Einstein condensation, by rapidly cooling a chromium multi-component Bose
gas. Despite relatively strong spin-dependent interactions, the critical
temperature for Bose-Einstein condensation is reached before the spin-degrees
of freedom fully thermalize. The increase in density due to Bose-Einstein
condensation then triggers spin dynamics, hampering the formation of
condensates in spin excited states. Small metastable spinor condensates are
nevertheless produced, and manifest strong spin fluctuations.Comment: 5 pages, 4 figure
Spontaneous demagnetization of a dipolar spinor Bose gas at ultra-low magnetic field
Quantum degenerate Bose gases with an internal degree of freedom, known as
spinor condensates, are natural candidates to study the interplay between
magnetism and superfluidity. In the spinor condensates made of alkali atoms
studied so far, the spinor properties are set by contact interactions, while
magnetization is dynamically frozen, due to small magnetic dipole-dipole
interactions. Here, we study the spinor properties of S=3 Cr atoms, in
which relatively strong dipole-dipole interactions allow changes in
magnetization. We observe a phase transition between a ferromagnetic phase and
an unpolarized phase when the magnetic field is quenched to an extremely low
value, below which interactions overwhelm the linear Zeeman effect. The BEC
magnetization changes due to magnetic dipole-dipole interactions that set the
dynamics. Our work opens up the experimental study of quantum magnetism with
free magnetization using ultra-cold atoms.Comment: 6 pages, 4 figures, 2 appendice
A High Flux Source of Cold Rubidium
We report the production of a continuous, slow, and cold beam of 87-Rb atoms
with an unprecedented flux of 3.2 x 10^12 atoms/s and a temperature of a few
milliKelvin. Hot atoms are emitted from a Rb candlestick atomic beam source and
transversely cooled and collimated by a 20 cm long atomic collimator section,
augmenting overall beam flux by a factor of 50. The atomic beam is then
decelerated and longitudinally cooled by Zeeman slowing
Cooling of a Bose-Einstein Condensate by spin distillation
We propose and experimentally demonstrate a new cooling mechanism leading to
purification of a spinor Bose-Einstein Condensate (BEC). Our scheme starts with
a BEC polarized in the lowest energy spin state. Spin excited states are
thermally populated by lowering the single particle energy gap set by the
magnetic field. Then these spin-excited thermal components are filtered out,
which leads to an increase of the BEC fraction. We experimentally demonstrate
such cooling for a spin 3 52Cr dipolar BEC. Our scheme should be applicable to
Na or Rb, with perspective to reach temperatures below 1 nK.Comment: 4 figure
Non-equilibrium quantum magnetism in a dipolar lattice gas
Research on quantum magnetism with ultra-cold gases in optical lattices is
expected to open fascinating perspectives for the understanding of fundamental
problems in condensed-matter physics. Here we report on the first realization
of quantum magnetism using a degenerate dipolar gas in an optical lattice. In
contrast to their non-dipolar counterparts, dipolar lattice gases allow for
inter-site spin-spin interactions without relying on super-exchange energies,
which constitutes a great advantage for the study of spin lattice models. In
this paper we show that a chromium gas in a 3D lattice realizes a lattice model
resembling the celebrated t-J model, which is characterized by a
non-equilibrium spinor dynamics resulting from inter-site Heisenberg-like
spin-spin interactions provided by non-local dipole-dipole interactions.
Moreover, due to its large spin, chromium lattice gases constitute an excellent
environment for the study of quantum magnetism of high-spin systems, as
illustrated by the complex spin dynamics observed for doubly-occupied sites.Comment: 10 pages, 5+5 figure
ETUDE EXPERIMENTALE ET THEORIQUE DES FLUCTUATIONS QUANTIQUES DE CHAMPS ET D'ATOMES COUPLES EN CAVITE
PARIS-BIUSJ-Physique recherche (751052113) / SudocCentre Technique Livre Ens. Sup. (774682301) / SudocSudocFranceF
Relaxation of the Collective Magnetization of a Dense 3D Array of Interacting Dipolar S = 3 Atoms
International audienc
Measuring Correlations from the Collective Spin Fluctuations of a Large Ensemble of Lattice-Trapped Dipolar Spin-3 Atoms
International audienceWe perform collective spin measurements to study the buildup of two-body correlations between â104 spin s=3 chromium atoms pinned in a 3D optical lattice. The spins interact via long range and anisotropic dipolar interactions. From the fluctuations of total magnetization, measured at the standard quantum limit, we estimate the dynamical growth of the connected pairwise correlations associated with magnetization. The quantum nature of the correlations is assessed by comparisons with analytical short- and long-time expansions and numerical simulations. Our Letter shows that measuring fluctuations of spin populations for s>1/2 spins provides new ways to characterize correlations in quantum many-body systems
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