Bose-Fermi Degeneracy in a Micro-Magnetic Trap

1. Bose-Fermi Degeneracy in a Micro-Magnetic Trap Seth A. M. Aubin University of Toronto / Thywissen Group February 25, 2006 CIAR Ultra-cold Matter Workshop, Banff. Work supported by NSERC, CFI, OIT, PRO and Research Corporation.

2. Outline • Motivation • Micro-magnetic traps and apparatus • Boson and Fermion degeneracy • Surprises in Rb-K scattering • Future experiments

3. Why ultra-cold bosons and fermions? • Objectives: • Condensed matter physics. • Boson-fermion mixtures. • Atom interferometry. Why on a chip? • Advantages: • Short experimental cycle. • Single UHV chamber. • Complex multi-trap geometries.

4. Z-trap current Evaporated Ag and Au (B. Cieslak and S. Myrskog) Trap Potential: Z-wire trap defects Iz RF for evaporation Micro-Magnetic Trap • Technology: • Electroplated gold wires on a silicon substrate. • Manufactured by J. Estève (Aspect/Orsay).

8. Solution: Use LIAD to control pressure dynamically !  405nm LEDs (power=600 mW) in a pyrex cell. Light-Induced Atom Desorption (LIAD) • Conflicting pressure requirements: • Large Alkali partial pressure  large MOT. • UHV vacuum  long magnetic trap lifetime.

9. Rapid High Efficiency Bose-Fermi Degeneracy

10. 10-13 10-6 1 105 PSD thermal atoms MOT magnetic trapping evap. cooling BEC Evaporation Efficiency High Efficiency Evaporation of 87Rb

11. RF@1.660 MHz: N=1.4x105, T<Tc RF@1.725 MHz: N = 6.4x105, T~Tc RF@1.740 MHz: N = 7.3x105, T>Tc Surprise! Reach Tc with only a 30x loss in number. (trap loaded with 2x107 atoms)  Experimental cycle = 5 - 15 seconds 87Rb BEC

12. 104 102 100 105 106 107 Cooling Efficiency 10-2 Phase Space Density 10-4 10-6 10-8 Atom Number Sympathetic Cooling of fermionic 40K with bosonic 87Rb

13. Optical Density EF 0 200 400 Radial distance (m) Fit Residuals 0 200 400 Radial distance (m) Non-Gaussian Distribution 1st signature of Fermi Degeneracy Fit: N = 4104 TF = 960 nK T/TF = 0.14(2) z = 1.4103 Residuals: Non-Thermal Distribution

14. EF Fermi Boltzmann Gaussian Fit EK,release/EF kTRb/EF Pauli Pressure -- 2nd signature of Fermi Degeneracy

15. Surprises with Rb-K cold collisions

16. Collision Rates Rb-Rb Rb-K Sympathetic cooling should work really well !!! Naïve Scattering Theory Sympathetic cooling 1st try: • “Should just work !” -- Anonymous • Add 40K to 87Rb BEC  No sympathetic cooling observed !

17. Evaporation 3 times slower than for BEC Experiment: Sympathetic cooling only works for slow evaporation

18. TK40(K) Cross-Section Measurement Thermalization of 40K with 87Rb

19. Rb-K cross-section (nm2) What’s happening?

20. Future Experiments … come see the poster • Pauli Blocking of light scattering: • Fermi sea reduces number of states an excited atom can recoil into. • Atomic lifetime increases, linewidth decreases. B. DeMarco and D. Jin, Phys. Rev. A58, R4267 (1998). • Species-specific trapping potentials ? • Bosons and fermions in different trapping potentials. • Isothermal “cooling” of fermions with bosons. • Boson-mediated interaction of fermions in an optical lattice. … or use a “magic” wavelength for Rb and K. C. Precilla and R. Onofrio, Phys. Rev. Lett.90, 030404 (2003).

21. EF First time on a chip ! arXiv: cond-mat/0512518 Summary • 87Rb BEC with up to 2105 atoms.  cycle time as short as 5 s. • 40K Fermi degeneracy: T/TF~0.1 with 4104 atoms.  Sympathetic cooling to 0.1TF in 6 s.  cycle time of 30 s. • Observation of severe reduction of Rb-K scattering cross-section at high T. • Bose-Fermi degeneracy in a chip trap.

22. Colors: Staff/Faculty Postdoc Grad Student Undergraduate S. Myrskog S. Aubin L. J. LeBlanc M. H. T. Extavour A. Stummer B. Cieslak J. H. Thywissen D. McKay Thywissen Group