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