Transcript Slide 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. Outline Motivation Apparatus Light Scattering: Simple approach Light Scattering: next generation 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). Rb + K Signatures of Degeneracy 87Rb Bose-Einstein Condensate: 104 - 105 atoms 0 Observation of Pauli Pressure EF Fermi-Dirac Statistics Boltzmann Statistics 200 400 Radial distance (m) EK,release/EF Optical Density Fermion (40K) momentum distribution 0.1TF with 4104 40K atoms S. Aubin et al., Nature Physics (2006). kTRb/EF Signatures of Degeneracy 87Rb Bose-Einstein Condensate: 104 - 105 atoms Fermion (40K) momentum distribution Observation of Pauli Pressure Fermi-Dirac Statistics Boltzmann Statistics 0 EK,release/EF Fit Residuals EF 200 400 Radial distance (m) 0.1TF with 4104 40K atoms S. Aubin et al., Nature Physics (2006). kTRb/EF Light Scattering with Fermions: Simple Approach Degenerate Fermions: Pauli Blocking of light scattering Probe Laser Fermi sea reduces number of states an excited atom can recoil into. DFG Atomic lifetime increases, linewidth decreases. B. DeMarco and D. Jin, Phys. Rev. A 58, R4267 (1998). Th. Busch et al., Europhys. Lett. 44, 755 (1998). Erecoil = 0.4 K EFermi = 1.1 K EFermi 2.75 Erecoil kF Further difficulty with Fermions We want this process kx More likely process Fermi Sea kx krec oil kx Fermi Sea krec oil kx Almost no Pauli blocking. 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. kx Look for Pauli blocking of decay into mf = 9/2. Fermi Sea DFG, mf=7/2 krecoil kx Non-DFG, mf=9/2 How well does it work ? Suppression factor: Γ Maxwell Boltzmann EF,2 = 4Erecoil M, suppresion factor M Γ Fermi Dirac T=0 EF,2 = 6Erecoil EF,2 = 8Erecoil EF,1 EF,2 EF,1 EF,2 Theory for a spherical harmonic trap, based on: B. DeMarco and D. Jin, Phys. Rev. A 58, R4267 (1998). Th. Busch et al., Europhys. Lett. 44, 755 (1998). Implementation 11/2 F = 11/2 9/2 7/2 Procedure: 5/2 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). NonDFG DFG 9/2 7/2 5/2 F = 9/2 Measure population ratios. Look for a change in ratio as T is decreased. 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 Dipole Trap Currently installing a 1064 nm dipole trap: Aligned with Z-wire trap. It works! ~100% loading efficiency with 87Rb. Loading into the optical trap: 105 87Rb atoms at ~ 1 µK Summary EF Degenerate Bose-Fermi mixture on a chip. New scheme for light scattering with fermions. Fermi Sea Dipole trap installed. krecoil Thywissen Group S. Aubin D. McKay B. Cieslak S. Myrskog M. H. T. Extavour A. Stummer T. Schumm Colors: Staff/Faculty Postdoc Grad Student Undergraduate L. J. LeBlanc J. H. Thywissen 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. Trap Potential: Z-wire trap Chip by J. Esteve, Orsay. Simple Version 11/2 F = 11/2 9/2 7/2 Procedure: State preparation: prepare DFG in mf=9/2, and nothing in mf=7/2. 5/2 Apply weak excitation pulse to intrap atoms. (atom scatters less than 1 photon) Use Stern-Gerlach to image the states separately. DFG empty 9/2 7/2 5/2 F = 9/2 Measure population ratios. Look for a change in ratio as T is decreased. Cross-Section plot Implementation #2 11/2 9/2 F = 11/2 7/2 5/2 9/2 7/2 F = 9/2 5/2 Procedure: NonDFG DFG 9/2 7/2 5/2 F = 9/2 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. Rb-K cross-section (nm2) Sympathetical Cooling