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Roger DingDr. Daniel S. Elliott
John LorenzJuly 29, 2010
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Overall Project Goal:• Photoassociation of Li and Rb
My REU Goals:◦ Work on electronics to help control the dual-
species magneto-optical trap (MOT) Laser locking circuits Timing Controls
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Rb Repump Laser
Locking Circuit
Li Trapping and Repump Laser
Rb Trapping Laser
Locking Circuit
Locking Circuit
Timing Control
Timing Control
Timing Control
Dual-Species Magneto-Optical Trap (MOT)
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Using light to form molecules from atoms
J. M. Sage et al. “Optical Production of Ultracold Polar Molecules”
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Why LiRb?◦ Polar molecule ◦ More complicated than atoms
Potential applications:◦ Quantum computing
D. DeMille. “Quantum Computation with Trapped Polar Molecules”
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Magneto-Optical Trap◦ Used to trap and cool
atoms Requirements to trap
atoms:1. Velocity-dependent
force2. Position-dependent
force
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Principle ideas:◦ Photons carry momentum◦ Atoms can absorb photons◦ Conservation of momentum◦ Doppler shift
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85Rb~780nm
85Rb
J. Lorenz
3035.73 MHz
361.58 MHz
63.40 MHz
120.65 MHz
D2780.241 nm
85Rb2
3
3
2
2
3
4
22S1/2
22P1/2
22P3/2
29.37 MHz1
D1794.979 nm
Conservation of Momentum
v
p=hf/c
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Atom at rest:
Atom moving towards the right:
85Rb fL,RfL,L
v85Rb fL,R + fDfL,L - fD
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Red-detune the laser from the transition frequency by
Slow moving atoms
Fast moving atoms
85Rb fL,RfL,L
fL,L - fD fL,R + fD85RbvFnet
L R
fL
=fD=fD
L R
fL
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Principle Ideas:◦ Slow moving atoms◦ Zeeman effect◦ Selection rules
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Zeeman Effect Used to shift atomic
energy levels onto resonance
Slow Moving Atoms Too slow to
Doppler shift laser onto resonance
fD
fL
fL
fD
E=gL�BmFB
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Selection Rules In a magnetic field, atoms preferentially
absorb light depending on its polarization
University of Colorado. “Advanced Optics Lab: Laser Cooling and Trapping”
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A. Mills. “Nonlinear Ground-state Pump-probe Spectroscopy in Ultracold Rubidium: Raman-coupled Dressed State
Spectroscopy”
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+-
I
I
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Lasers must be tuned and kept at specific frequencies
Stabilizing lasers:◦ Temperature control◦ Current control◦ Electronic feedback
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Peak Locking
Small capture range:◦ Accurate ◦ Sensitive to
disturbances
Dichroic Atomic Vapor Laser Lock (DAVLL)
Large capture range:◦ Robust◦ Tendency to drift
f
V
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Idea: take the “derivative” of the Doppler-free saturated absorption signal
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Rb Cell Rb Cell
Doppler broadening “Hole burning”
87RbF=2
85RbF=3
85RbF=2
87RbF=1
87RbF=2
85RbF=3
85RbF=2
87RbF=1
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Rb Cell
Doppler-free saturated absorption
87RbF=2
85RbF=3
85RbF=2
87RbF=1
Physical implementation of Doppler-free saturated absorption
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F=3
2-3 C.O.
2-4 C.O.
F=4
3-4 C.O.
Close-up of 85Rb hyperfine peaks
F=2
Doppler-free saturated absorption87Rb
F=285RbF=3
85RbF=2
87RbF=1
Look at 85Rb F=3 ground state
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Hyperfine Peaks Crossover Resonances
F=3
F=2
F=3
F=3
F=2
F=3
-fD
+fD
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1. Apply a dither to the Doppler-free saturated absorption signal
2. Use a lock-in amplifier and low-pass filter to convert amplitude of dither on signal to voltage
Dither
Lock-in +Low-pass
f
Abs.
f
Abs.
f
Abs.
f
V
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Idea: in a magnetic field, atoms absorb light differently depending on its polarization
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f
Abs.
f
Abs.
Rb Cell+
-
B
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A. Mills. “Nonlinear Ground-state Pump-probe Spectroscopy in Ultracold Rubidium: Raman-coupled Dressed State
Spectroscopy”
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Want benefits of both peak locking and DAVLL schemes◦ Accurate◦ Robust
Brute force approach
Peak Locking
DAVLL +
_ Error Signal
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Have not yet had the chance to do extensive testing
Appears to be somewhat quirky:◦ Does not yet lock as well as we had hoped
Improvements:◦ Tweak component values◦ Adjust error signals◦ Better method of combining signals
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Need method of controlling multiple acousto-optic modulators for the dual-species MOT
Interface with National Instruments data acquisition card
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AOMs are used for:◦ Frequency shifting◦ Fast shutters
RP Photonics “Acousto-optic Modulators”
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Voltage Controlled Oscillator
(VCO)
RF Switch
Voltage Controlled Attenuator
National Instruments Card
AmplifierAcousto-Optic
Modulator (AOM)
Voltage Controlled Oscillator
(VCO)
AmplifierAcousto-Optic
Modulator (AOM)
x6
x2
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My projects involved working on control mechanisms for the dual-species MOT◦ Laser locking circuits◦ AOM controller board
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Dr. Daniel S. Elliott Dr. Sergei Savikhin John Lorenz Adeel Altaf Dionysios Antypas