1 / 34

The Pennsylvania State University Ken O’Hara Jason Williams Eric Hazlett Ronald Stites Yi Zhang

Stability of a Fermi Gas with Three Spin States. The Pennsylvania State University Ken O’Hara Jason Williams Eric Hazlett Ronald Stites Yi Zhang John Huckans. Three-Component Fermi Gases. Many-body physics in a 3-State Fermi Gas

tanner-delacruz
Download Presentation

The Pennsylvania State University Ken O’Hara Jason Williams Eric Hazlett Ronald Stites Yi Zhang

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Stability of a Fermi Gas with Three Spin States The Pennsylvania State University Ken O’Hara Jason Williams Eric Hazlett Ronald Stites Yi Zhang John Huckans

  2. Three-Component Fermi Gases • Many-body physics in a 3-State Fermi Gas • Mechanical stability with resonant interactions an open question • Novel many-body phases • Competition between different Cooper pairs • Competition between Cooper pairing and 3-body bound states • Analog to Color Superconductivity and Baryon Formation in QCD • Polarized 3-state Fermi gases: Imbalanced Fermi surfaces • Novel Cooper pairing mechanisms • Analogous to mass imbalance of quarks

  3. QCD Phase Diagram C. Sa de Melo, Physics Today, Oct. 2008

  4. Simulating the QCD Phase Diagram • Color Superconducting-to-“Baryon” Phase Transition • 3-state Fermi gas in an optical lattice • Rapp, Honerkamp, Zaránd & Hofstetter, PRL 98, 160405 (2007) • A Color Superconductor in a 1D Harmonic Trap • Liu, Hu, & Drummond, PRA 77, 013622 (2008) • Rapp, Hofstetter & Zaránd, • PRB 77, 144520 (2008)

  5. Universal Three-Body Physics • The Efimov Effect in a Fermi system • Three independent scattering lengths • More complex than Efimov’s original scenario • New phenomena (e.g. exchange reactions) • Importance to many-body phenomena • Two-body and three-body physics completely described • Three-body recombination rate determines stability of the gas

  6. Three-State 6Li Fermi Gas Hyperfine States of 6Li

  7. Inelastic Collisions • No Spin-Exchange Collisions • Energetically forbidden • (in a bias field) • Minimal Dipolar Relaxation • Suppressed at high B-field • Electron spin-flip process irrelevant in electron-spin-polarized gas • Three-Body Recombination • Allowed in a 3-state mixture • (Exclusion principle suppression for 2-state mixture)

  8. Making and Probing 3-State Mixtures Radio-frequency magnetic fields drive transitions 0 200 400 600 800 1000 Magnetic Field (Gauss) Spectroscopically resolved absorption imaging

  9. The Resonant QM 3-Body Problem (1970) Efimov: An infinite number of bound 3-body states for . · · · Inner wall B.C. determined by short-range interactions Vitaly Efimov circa 1970 Infinitely many 3-body bound states (universal scaling): A single 3-body parameter:

  10. QM 3-Body Problem for Large a & (1970 & 1971) Efimov: Identical Bosons in Universal Regime • Observable for a < 0: • Enhanced 3-body recombination rate at E. Braaten, et al. PRL 103, 073202 • Note: • Only two free parameters: • Log-periodic scaling: Diagram from: E. Braaten & H.-W. Hammer,Ann. Phys. 322,120 (2007)

  11. Universal Regions in 6Li

  12. The Threshold Regime and the Unitarity Limit • Universal predictions only valid at threshold • Collision Energy must be small • Smallest characteristic energy scale • Comparison to theory requires low temperature • and low density (for fermions) • Recombination rate unitarity limited in a thermal gas

  13. Making Fermi Gases Cold • Evaporative Cooling in an Optical Trap • Optical Trap Formed from two 1064 nm, 80 Watt laser beams • Create incoherent 3-state mixture • Optical pumping into F=1/2 ground state • Apply two RF fields in presence of field gradient

  14. Making Fermi Gases Ultracold Adiabatically Release Gas into a Larger Volume Trap

  15. Low Field Loss Features Resonance Resonance T. B. Ottenstein et al., PRL 101, 203202 (2008). J. H. Huckans et al., PRL102, 165302 (2009). Resonances in the 3-Body Recombination Rate!

  16. Measuring 3-Body Rate Constants Loss of atoms due to recombination: Evolution assuming a thermal gas at temperature T : “Anti-evaporation” and recombination heating:

  17. Recombination Rate in Low-Field Region

  18. Recombination Rate in Low-Field Region P. Naidon and M. Ueda, PRL 103, 073203 (2008). E. Braaten et al., PRL 103, 073202 (2009). S. Floerchinger, R. Schmidt, and C. Wetterich, Phys. Rev. A 79, 053633 (2009)

  19. Recombination Rate in Low-Field Region P. Naidon and M. Ueda, PRL 103, 073203 (2008). E. Braaten et al., PRL 103, 073202 (2009). S. Floerchinger, R. Schmidt, and C. Wetterich, Phys. Rev. A 79, 053633 (2009) Better agreement if h* tunes with magnetic field – A. Wenz et al., arXiv:0906.4378 (2009).

  20. Efimov Trimer in Low-Field Region

  21. 3-Body Recombination in High Field Region

  22. 3-Body Recombination in High Field Region

  23. Determining the Efimov Parameters using calculations from E. Braaten et al., PRL 103, 073202 (2009).

  24. Determining the Efimov Parameters using calculations from E. Braaten et al., PRL 103, 073202 (2009).

  25. Determining the Efimov Parameters using calculations from E. Braaten et al., PRL 103, 073202 (2009).

  26. Efimov Trimers in High-Field Region also predicts 3-body loss resonances at 125(3) and 499(2) G

  27. 3-Body Observables in High Field Region from E. Braaten, H.-W. Hammer, D. Kang and L. Platter, arXiv (2009).

  28. Prospects for Color Superfluidity • Color Superfluidity in a Lattice (increased density of states) • TC= 0.2 TF(in a lattice with d= 2 mm, V0= 3ER ) • Atom density ~1011 /cc • Atom lifetime ~ 200 ms (K3 ~ 5 x 10-22 cm6/s) • Timescale for Cooper pair formation

  29. Summary • Observed variation of three-body recombination rate by 8 orders of magnitude • Experimental evidence for ground and excited state Efimov trimers in a three-component Fermi gas • Observation of Efimov resonance near three overlapping Feshbach resonances • Determined three-body parameters in the high field regime which is well described by universality • The value of k* is nearly identical for the high-field and low-field regions despite crossing non-universal region • Three-body recombination rate is large but does not necessarily prohibit future studies of many-body physics

  30. Fermi Gas Group at Penn State Ken O’Hara John HuckansRon Stites Eric Hazlett Jason Williams Yi Zhang

  31. Future Prospects • Efimov Physics in Ultracold Atoms • Direct observation of Efimov Trimers • Efimov Physics (or lack thereof) in lower dimensions • Many-body phenomena with 3-Component Fermi Gases

More Related