Transcript Slide 1

Spatial distributions in a
cold strontium Rydberg gas
Graham Lochead
Rydberg states
High principal quantum number n
Ionization limit
n = 68
n = 67
n = 66
n=8
n=7
Properties
n=6
H ~ 0.1 nm
n=5
n = 100 ~ 1 μm
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Dipole blockade
Strong, tunable interactions
M. Saffman et al., Rev. Mod. Phys. 82 2313 (2010)
C.L. Vaillant et al., J. Phys. B 45 135004 (2012)
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Experimental dipole blockade
Saturation of excitation
H. Schempp et al, Phys. Rev. Lett. 104, 173602 (2010)
Enhanced Rabi frequency
Two atoms
One atom
A. Gaëtan et al, Nature Physics 5, 115 (2009)
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Dipole blockade directions
CNOT gate operation
L. Isenhower et al, Phys. Rev. Lett. 104, 010503 (2010)
Single photon emitter
Y. O. Dudin et al, Science 336, 887 (2012)
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Dipole blockade spatial effects
Excited state
Column
density
Autocorrelation
Ground state
Radius (μm)
Position
A. Schwartzkopf et al., Phys. Rev. Lett. 107, 103001 (2011)
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Further spatial effects
Dynamical crystallisation
P. Schauß et al., arXiv:1209.0944
T. Pohl et al., Phys. Rev. Lett. 104, 043002 (2010)
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Outline
• Coherent Rydberg excitation
• Laser stabilization
• CPT in cold strontium atoms
• Optical Bloch Equation model
• Two electron information
• State transfer
• Autoionization microscopy
• Statistical distributions
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Dispenser cell
Need atomic reference cell
Problems:
• No vapour pressure at room temperature
• Strontium reacts with glass
Solution:
• Dispenser-based cell
E. M. Bridge et. al., Rev. Sci. Instrum. 80, 013101 (2009)
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Probe/cooling laser stabilization
Sub-Doppler frequency modulation spectroscopy
5snd
Coupling
λ2 = 413 nm
5s5p
Probe
λ1 = 461 nm
5s2
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Coupling laser stabilization
EIT-based lock
5snd
Coupling
λ2 = 413 nm
5s5p
Probe
λ1 = 461 nm
5s2
M. Fleischhauer et al, Rev. Mod. Phys. 77, 633 (2005)
R. P. Abel et al, Appl. Phys. Lett. 94, 071107 (2009)
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Cold atom source
• Zeeman slowed atomic beam
• 107 strontium atoms at 5 mK
• 5 x 109 atoms/cm3
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Chamber insides
R. Löw et al, arXiv:0706.2639v1
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Detecting Rydberg atoms
Small signal
– number resolving
Large signal
– average only
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CPT spectra
• Coupling laser locked
• Probe laser frequency stepped
• E-field does not field ionize
• Sub-natural linewidth
• Data for n = 56
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Optical Bloch Equations
5snd
Ωc
5s5p
Free parameters
• Laser linewidths
• Rabi frequencies
• Laser detuning
• State linewidths
• Amplitude scaling
Ωp
Fixed parameters
5s2
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Why strontium?
Two valence electrons
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Autoionization
• Resonant optical ionization for l < 8
• Independent of excitation
W.E. Cooke et al, Phys. Rev. Lett. 40, 178 (1978)
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Temporal information
Pulsed dye laser used for this
experiment, ECDL for the rest
J. Millen et al, J. Phys. B 44 184001 (2011)
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Spectral information
Low Rydberg density
High Rydberg density
• Shape depends on state
• Multi-channel quantum defect fit
E. Y. Xu et al., Phys. Rev. A 35, 1138 (1987)
J. Millen et al., Phys. Rev. Lett. 105, 213004 (2010)
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State transfer
At high density allow the Rydberg gas to evolve:
Δt = 0.5 μs
Δt = 60 μs
Δt = 100 μs
At low density spectrum unchanged
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Lifetime analysis
Look at the decay of signal at different spectral points:
Δt = 100 μs
54F state
60μs
25μs
A
B
25μs
A
B
Blue line: The decay of the 5s54f 1F3 state.
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60μs
Including 5s54f state
13 ± 3% of the Rydberg population transferred to 5s54f state
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Mechanism
The mechanism for population transfer is cold plasma formation:
Plasma threshold
Spontaneous ionization
Population transferred
• l-changing collisions
Initial Rydberg #
Black data: population
transfer
Red data: spontaneous
ionization
M. P. Robinson et. al., Phy. Rev. Lett. 85, 4466 (2000)
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Focus coupling laser
Fewer Rydberg atoms – no plasma formation
Spatial intensity variation of
beam makes a difference
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Spatial information
Translate a focused autoionizing beam
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Lens setup
100 mm long
10 μm resolution
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Rydberg spatial distribution
• Ground state fluorescence collected
• Can take distributions in both directions
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Spatial widths: Coupling power
OBE
simulation
Autoionizing
probability
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Spatial widths: Autoionizing power
T.F. Gallagher, Rydberg Atoms
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Detection efficiency
ng : ground state density
Pde → 1
V : overlap volume
ρ33 : Rydberg probability
C : single ion conversion
ε: detector efficiency
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ε = 21 ± 4 %
Statistical information
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Towards blockade
n = 75
1P
3P
1
3P
λ = 461 nm
Γ = 2π x 32 MHz
1st stage cooling
1S
3P
2
1
0
λ = 689 nm
Γ = 2π x 7.5 kHz
2nd stage cooling
0
Blue MOT: ~ 5 mK
~ 2 x 109 atoms/cm3
Red MOT: ~ 400 nK
~ 2 x 1012 atoms/cm3
H. Schempp et al., Phys. Rev. Lett. 104, 173602 (2010)
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Electrometry
Use Stark effect to alter Rydberg distribution
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Summary
•
Coherently excite strontium atoms to Rydberg states
•
10 µm resolution spatial distribution
•
Number resolving technique
•
No interactions seen
→ Implement second stage cooling
Thanks for listening
Graham Lochead 06/11/12
The group
Matt Jones
Charles Adams
Liz Bridge
James Millen
Danielle Boddy
Daniel
Christophe
Sadler
Vaillant
Graham Lochead 06/11/12
Graham Lochead 06/11/12