Bose-Einstein condensation in Chromium and rf-assisted dipolar collisions

1. Bose-Einstein condensation in Chromiumand rf-assisted dipolar collisions Laboratoire de Physique des Lasers Université Paris Nord Villetaneuse - France Bruno Laburthe Tolra

2. Chromium : S=3 Large magnetic Dipole-dipole interactions Interesting spinor structure Large sensitivity to (rf) magnetic fields - Rf control of Landé factor - rf-assisted collisions BEC: Stuttgart 2004 Villetaneuse 2007 Santos and Pfau PRL 96, 190404 (2006) Rf-induced ground state degeneracy Stuttgart: d-wave collapse 1050 kHz 900 kHz 700 kHz 500 kHz 400 kHz 400 kHz 300 kHz Pfau, PRL 101, 080401 (2008)

3. The Villetaneuse roadmap to ChromiumBECs. 7P4 7P3 650 nm 600 425 nm 550 5S,D (2) (1) 500 427 nm Z 450 500 550 600 650 700 750 7S3 • An atom: 52Cr • An oven • A Zeeman slower MOT 52Cr / 53Cr Magnetic trap Oven at 1550 °C (Rb 150 °C) • A small MOT (Rb=780 nm) N = 4.106 Optical trap optimized (Rb=109 or 10) Optical trap Stuttgart roadmap: Load a magnetic trap And evaporate d-wave Feshbach resonance BEC in strong rf field Rf association BEC • A dipole trap • A BEC every 15 s • All optical evaporation • A crossed dipole trap

4. Rf control of the Landé factor Modify the Landé factor of the atomsgJwithverystrong off resonantrffields. If the RF frequencyωislargerthan the Larmor frequencyω0,then: Eigenenergies Rf power A spinor is a multicomponent BEC (with degenerate components): the magnetic fields needs to be small (interaction energy > Zeeman energy) < 1 mG !!... • Serge Haroche thesis • S.Haroche, et al., PRL 24 16 (1970) • True in 2D… Generalization in 3D ? 3 2 1 0 -1 -2 -3 Can we use this degeneracy for spinor physics ?

5. Control magnetism Weapplybluedetunedrffields to a Cr BEC in a one beamopticaltrap, plus a magneticfield gradient. B = 0 at the center of the trap. The atoms, highfieldseekers, leave the center of the trap. RF modifies the effect of such a gradient: Rf dressing is reversible (adiabatic)

6. Collision properties of off-resonantly rf dressed states : Elastic s-wave collisions: Rf does not couple different molecular potentials -> s-wave elastic collisions should be unchanged. Dipolar interactions: No rf répulsive attractive Rf perpendicular to static field : a new geometrical dependence ! q f

7. N+1 w N N-1 Inelastic collision properties of off-resonantly rf dressed states : Beware of the lowest energy state argument !!

8. Interpretation: an rf-assisted dipolar relaxation Gap ~ Similar mechanism than dipolar relaxation Within first order Born approximation: In collaboration with Anne Crubellier (LAC – Ifraf) and Paolo Pedri (Ifraf postdoc in our group)

9. Why Bessel functions ? Analytical expression for dressed state (from C. Cohen-Tannoudji) First order perturbation theory: Anotherinterestingrf-assisted collision: Rf association of molecules near a Feshbachresonance d-wave Feshbach resonnance due to dipolar interactions 1050 kHz 900 kHz 700 kHz 500 kHz 400 kHz 400 kHz 300 kHz 18 mK 14 mK 10 mK 6 mK 4 mK 1050 kHz 700 kHz 500 kHz 400 kHz 400 kHz 300 kHz

10. Future • Optical lattices – dipolar gases in reduced dimensions • Feshbach resonances – pure dipolar gases • Fermions – degenerate Fermi sea with polarized atoms with dipole interactions

11. L. Vernac E. Maréchal J. C. Keller G. Bismut Paolo Pedri B. Laburthe B. Pasquiou Q. Beaufils O. Gorceix Have left: T. Zanon, R. Barbé, A. Pouderous, R. Chicireanu Collaboration:Anne Crubellier (Laboratoire Aimé Cotton)