LKB - Bose-Einstein condensates

Sodium spinor condensates

Research

Phase diagram of antiferromagnetic spinor condensates

We have measured the magnetic phase diagram of antiferromagnetic spin 1 condensates in equilibrium. Two phases are competing against each other, reflecting the competition between spin-exchange interactions and the (quadratic) Zeeman energy in an applied magnetic field. This competition leads to a quantum phase transition from an “antiferromagnetic” state, where m=0 is absent, to a “mixed” or “broken-axisymmetry” state where the population in m=0 does not vanish and increases with the applied magnetic field. The measured phase diagram shows this population (normalized to the total atom number) as a function of the two experimental control parameters, the longitudinal magnetization mz and of the applied magnetic field B (or equivalently, of the quadratic Zeeman energy). A sequence of images for a fixed magnetization and increasing magnetic fields is also shown, demonstrating visually the phase transition.

References :

  • D. Jacob, L. Shao, V. Corre, T. Zibold, L. De Sarlo, E. Mimoun, J. Dalibard, and F. Gerbier, Phase diagram of antiferromagnetic spin 1 Bose-Einstein condensates, Phys. Rev. A 86, 061601(R); arXiv:1209.2533 (2012).
  • T. Zibold, V. Corre, C. Frapolli, A. Invernizzi, J. Dalibard, and F. Gerbier, Spin-nematic order in antiferromagnetic spinor condensates, Phys. Rev. A 93, 023614 (2016); arXiv:1506.06176.

Stern-Gerlach imaging of a spinor condensate

Condensates produced in the optical trap are inherently spinor, as all three Zeeman states in the hyperfine spin F=1 manifold are trapped with the same strength. We detect the spin composition of the atomic sample using a time-of-flight technique, releasing the atoms from the trap while simultaneously applying a magnetic field gradient that separates the spin components according to their magnetic moments (as in the historical experiment by O. Stern and W. Gerlach). The picture shows a snapshot of a Sodium Bose-Einstein condensate taken using this Stern-Gerlach imaging technique, showing all three Zeeman components.

Preparing a spinor condensate in a microtrap

In our experiment, Sodium atoms are introduced using dispensers inside the vacuum chamber. LIADThey quickly deposit on the chamber walls and viewports surfaces. Using strong near-ultraviolet light emitted by power LEDs and the light-induced atomic desorption (LIAD) effect, we are able to modulate the Sodium partial pressure in the chamber by a factor 50, going from a situation where a magneto-optical trap (MOT) can be efficiently loaded to a situation with much better vacuum for evaporation in an optical trap. We trap typically a few tens millions atoms in the MOT after several seconds loading. Once the atoms are laser-cooled in the MOT, we turn on a crossed optical trap formed by a 1070 nm laser focused down to 40 microns and folded onto itself. After loading, MOT lasers are switched off and atoms, which are now “in the dark”, can relax via elastic collisions to a kinetic equilbrium state. During this phase, the depth of the dipole trap is fixed, and atoms can accumulate in the crossing region. A dense sample builds up there, allowing us to perform evaporative cooling.

BECProfileAfter about one second of evaporation, atoms are transferred to a secondary crossed dipole trap to improve the efficiency of evaporative cooling (the so-called “dimple trap” technique). This second trap, more focused than the first one, (about 10 microns 1/e2 waist) boosts the spatial density (and thus the collision rate), allowing us to produce small “microcondensates” of a few thousand atoms.

Condensates produced in the optical trap are inherently spinor, as all three Zeeman states in the hyperfine spin F=1 manifold are trapped with the same strength. We detect the spin composition of the atomic sample using a time-of-flight technique, releasing the atoms from the trap while simultaneously applying a magnetic field gradient that separates the spin components according to their magnetic moments (as in the historical experiment by O. Stern and W. Gerlach). The picture shows a snapshot of a Sodium Bose-Einstein condensate taken using this Stern-Gerlach imaging technique, showing all three Zeeman components.

References:

  • D. Jacob, E. Mimoun, L. DeSarlo, M. Weitz, J. Dalibard, F. Gerbier, Production of sodium Bose–Einstein condensates in an optical dimple trap, New J. Phys. 13, 065022 (2011); arXiv:1104.1009.
  • E. Mimoun, L. de Sarlo, D. Jacob, J. Dalibard, F. Gerbier, Fast production of ultracold sodium gases using light-induced desorption and optical trapping,Phys. Rev A 81, 023631 (2010);arXiv:0911.5656

 

An all-solid-state laser for laser cooling of Sodium atoms

sodium_S1aCollaboration : Jean-Jacques Zondy (INM-CNAM)

Our experiment relies on a home-designed and built laser system emitting at 589 nm (the wavelength of the famous yellow doublet of Sodium). Our approach relies on sum-frequency generation from two monolithic YAG lasers at 1320 nm and 1064 nm. We demonstrated a conversion efficiency of 90%, with output power as high as 700 mW starting from 0.5 W and 1 W from the two infrared pumps. A patented locking system [*] was essential to obtain this conversion efficiency. This work was done as part of the PhD thesis of Emmanuel Mimoun, and performed in collaboration with Jean-Jacques Zondy (INM-CNAM).

References :

  • E. Mimoun, L. de Sarlo, J.-J. Zondy, J. Dalibard, and F. Gerbier, All solid-state laser system for laser cooling of sodium, Applied Physics B 99, 31 (2010); arXiv:0908.0279. arXiv:0908.0279.
  • E. Mimoun, L. de Sarlo, J.-J. Zondy, J. Dalibard, and F. Gerbier, Sum-frequency generation of 589 nm light with near-unit efficiency, Optics Express 16, 18684-18691 (2008); arXiv:0807.2965.
  • [*] Brevet INPI 0803153 (6 juin 2008) : Dispositif optique de conversion de longueur d’onde et source de lumière utilisant un tel dispositif; US Patent 8,717,665 (2014) : Optical wavelength conversion device, and coherent light source using same.