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? Advantages:  Short experimental cycle.  Single UHV chamber.  Complex multi-trap geometries. Advantages:  Short experimental cycle.  Single UHV chamber.  Complex multi-trap geometries. Why on a chip? Objectives:  Condensed matter physics.  Boson-fermion mixtures.  Atom interferometry. Objectives:  Condensed matter physics.  Boson-fermion mixtures.  Atom interferometry.

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

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

9. Rapid High Efficiency Bose-Fermi Degeneracy

10. High Efficiency Evaporation of 87 Rb Evaporation Efficiency BEC thermal atoms magnetic trapping evap. cooling MOT 10 -13 110 -6 10 5 PSD

11. 87 Rb BEC Surprise! Reach T c with only a 30x loss in number. (trap loaded with 2x10 7 atoms)  Experimental cycle = 5 - 15 seconds RF@1.740 MHz: N = 7.3x10 5, T>T c RF@1.725 MHz: N = 6.4x10 5, T~T c RF@1.660 MHz: N=1.4x10 5, T<T c

12. Sympathetic Cooling of fermionic 40 K with bosonic 87 Rb Cooling Efficiency 10 -8 10 -6 10 -4 10 -2 10 0 10 2 10 4 10 5 10 6 10 7 Atom Number Phase Space Density

13. Non-Gaussian Distribution 1 st signature of Fermi Degeneracy Optical Density 0200400 Radial distance (  m) Fit Residuals 0200400 Radial distance (  m) Fit: Residuals: N = 4  10 4 T F = 960 nK T/T F = 0.14(2) z = 1.4  10 3 N = 4  10 4 T F = 960 nK T/T F = 0.14(2) z = 1.4  10 3 Non-Thermal Distribution EFEF

14. EFEF kT Rb /E F E K,release /E F Pauli Pressure -- 2 nd signature of Fermi Degeneracy Fermi Boltzmann Gaussian Fit

15. Surprises with Rb-K cold collisions

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

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

18. Cross-Section Measurement T K40 (  K) Thermalization of 40 K with 87 Rb

19. What’s happening? Rb-K cross-section (nm 2 )

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. A 58, R4267 (1998). 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. A 58, 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. 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. Summary  87 Rb BEC with up to 2  10 5 atoms.  cycle time as short as 5 s.  40 K Fermi degeneracy: T/T F ~0.1 with 4  10 4 atoms.  Sympathetic cooling to 0.1T F 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. EFEF First time on a chip ! arXiv: cond-mat/0512518

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