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Progress on Light Scattering From Degenerate Fermions

Explore the modification of excited state lifetime/linewidth with quantum statistics in light scattering experiments with degenerate fermions. Investigation into reducing recoil states and increasing lifetime. Discussion of Pauli blocking effects and comparisons with condensed matter systems to enhance understanding. Implementation and challenges in manipulating Fermi energies for increased likelihood of processes.

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Progress on Light Scattering From Degenerate Fermions

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  1. Progress on Light Scattering From Degenerate Fermions Seth A. M. Aubin University of Toronto / Thywissen Group May 20, 2006 DAMOP 2006 Work supported by NSERC, CFI, OIT, PRO and Research Corporation.

  2. Outline • Motivation • Apparatus • Light Scattering: Simple approach • Light Scattering: next generation

  3. Light Scattering with Fermions Objective: Modify the lifetime/linewidth of an excited state with quantum statistics. • Motivation: • Trapping environment reduces the number of recoil states  lifetime increases. • Analogous phenomena observed in cavity QED systems. • Similar phenomena frequently observed in condensed matter systems. See for example, A. Högele et al., Appl. Phys. Lett. 86, 221905 2005).

  4. Rb + K

  5. Optical Density 0 200 400 Observation of Pauli Pressure Radial distance (m) EF Fermi-Dirac Statistics Boltzmann Statistics EK,release/EF kTRb/EF Signatures of Degeneracy 87Rb Bose-Einstein Condensate: 104 - 105 atoms Fermion (40K) momentum distribution 0.1TF with 410440K atoms S. Aubin et al., Nature Physics (2006).

  6. Observation of Pauli Pressure EF Fit Residuals EK,release/EF 0 200 400 Radial distance (m) kTRb/EF Signatures of Degeneracy 87Rb Bose-Einstein Condensate: 104 - 105 atoms Fermion (40K) momentum distribution Fermi-Dirac Statistics Boltzmann Statistics 0.1TF with 410440K atoms S. Aubin et al., Nature Physics (2006).

  7. Probe Laser Erecoil = 0.4 K EFermi = 1.1 K Light Scattering with Fermions: Simple Approach • Degenerate Fermions: • 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). Th. Busch et al., Europhys. Lett.44, 755 (1998). DFG kF

  8. kx krecoil krecoil kx Fermi Sea kx Fermi Sea kx Further difficulty with Fermions We want this process More likely process  Almost no Pauli blocking.

  9. kx krecoil Fermi Sea DFG, mf=7/2 kx Non-DFG, mf=9/2 Solution ? IDEA: different states can have different Fermi energies/momentum (i.e. different populations), but still be in thermal equilibrium. • Excite mf = 7/2 atoms. • Look for Pauli blocking of decay into mf = 9/2.

  10. M, suppresion factor EF,2 = 4Erecoil EF,2 = 6Erecoil EF,2 = 8Erecoil How well does it work ? Suppression factor: T=0 EF,1 EF,2 Theory for a spherical harmonic trap, based on: B. DeMarco and D. Jin, Phys. Rev. A58, R4267 (1998). Th. Busch et al., Europhys. Lett.44, 755 (1998).

  11. 11/2 9/2 9/2 7/2 7/2 5/2 5/2 Implementation F = 11/2 • Procedure: • State preparation: prepare DFG in mf=7/2, and non-DFG in mf=9/2. • Apply weak excitation pulse (atom scatters less than 1 photon). • Measure population ratios. • Look for a change in ratio as T is decreased. Non-DFG DFG F = 9/2

  12. Potential Difficulties • Rescattering of scattered light.  far off resonance probe • Unwanted transitions to unsuppressed levels.  dipole trap + large Zeeman splittings • Heating due to probe.  short pulse

  13. Loading into the optical trap: 10587Rbatoms at ~ 1 µK Dipole Trap Currently installing a 1064 nm dipole trap:  Aligned with Z-wire trap.  It works!  ~100% loading efficiency with 87Rb.

  14. EF krecoil Fermi Sea Summary • Degenerate Bose-Fermi mixture on a chip. • New scheme for light scattering with fermions. • Dipole trap installed.

  15. 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 T. Schumm

  16. Chip by J. Esteve, Orsay. Trap Potential: Z-wire trap Atom Chip for Bose-Fermi mixtures • Advantages: • Short experimental cycle (5-40 s). • Single UHV chamber. • Complex multi-trap geometries. • On-chip RF and B-field sources.

  17. 11/2 9/2 9/2 7/2 7/2 5/2 5/2 Simple Version F = 11/2 • Procedure: • State preparation: prepare DFG in mf=9/2, and nothing in mf=7/2. • Apply weak excitation pulse to in-trap atoms. (atom scatters less than 1 photon) • Use Stern-Gerlach to image the states separately. • Measure population ratios. • Look for a change in ratio as T is decreased. DFG empty F = 9/2

  18. Cross-Section plot

  19. F = 11/2 11/2 F = 9/2 9/2 9/2 9/2 7/2 7/2 7/2 5/2 5/2 5/2 Implementation #2 • Procedure: • State preparation: prepare DFG in mf=9/2, and non-DFG in mf=7/2. • Apply 2-photon excitation pulse (1 RF + 1 optical). • Look for a decrease in scattering rate as T is decreased. DFG Non-DFG F = 9/2

  20. Rb-K cross-section (nm2) Sympathetical Cooling

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