Rydberg & plasma physics using ultra-cold strontium James Millen Supervisor: Dr. M.P.A. Jones Rydberg & plasma physics using ultra-cold strontium
Dec 21, 2015
Rydberg & plasma physics using ultra-cold strontium
James Millen
Supervisor: Dr. M.P.A. Jones
Rydberg & plasma physics using ultra-cold strontium
Outline
• The strontium experiment
• Introduction and motivation
• The strontium MOT
Rydberg & plasma physics using ultra-cold strontium
Rydberg physics
• A Rydberg state is one of high principle quantum number n
• Rydberg atoms can be very large (orbital radius scales as n2)
• Very strong Rydberg-Rydberg interactions (van-der-Waals interaction scales as n11)
• This can lead to “frozen” Rydberg gases, where the interaction energy is much greater than the thermal energy.
Johannes Rydberg
1854-1919
Rydberg & plasma physics using ultra-cold strontiumIntroduction
Ultra-cold plasma physics
• Most plasmas are hot, dense and dominated by their kinetic energy
• The behaviour of ultra-cold neutral plasmas is governed by Coulomb interactions
• Other “strongly coupled” plasmas are not accessible in the lab Killian, Science 316 705-708
Rydberg & plasma physics using ultra-cold strontiumIntroduction
Ultra-cold plasma physics
• Plasmas can be formed from cold atoms by optically exciting above the ionisation threshold
• Some electrons leave, leading to the system being bound
• Frozen Rydberg gasses spontaneously evolve into plasmas and visa versa(T. F. Gallagher, P. Pillet, D. A. Tate et al. Phys. Rev. A 70 042713 (2004)S.L. Rolston et al. Phys. Rev. Lett. 86, 17 (2001) )
Killian, Science 316 705-708
Rydberg & plasma physics using ultra-cold strontiumIntroduction
Rydberg & plasma physics using ultra-cold strontiumIntroduction
Long term goals of our project (!)
• Create a cold Rydberg gas / neutral plasma in a 1D lattice
• Lattice spacing can be on the order of the size of the Rydberg atoms
• Narrow linewidth transitions (7kHz) could lead to single site addressability.
Introduction to Strontium
• Atomic Number: 38
• An alkaline earth metal (Group II)
• Four naturally occurring isotopes: 88Sr (82.6%), 87Sr (7.0%), 86Sr (9.9%) & 84Sr (0.6%)
• 88,86,84Sr have no hyperfine structure (Bosonic I=0), 87Sr has I=9/2 (Fermionic)
• Negligible vapour pressure at room temperature(1 mTorr at 1000K)
Rydberg & plasma physics using ultra-cold strontiumIntroduction
88Sr energy level diagram
F. Sorrentino, G. Ferrari, N. Poli, R. Drullingerand G. M. Tino arXiv:physics/0609133v1
412.7nm
Rydberg & plasma physics using ultra-cold strontiumIntroduction
Why strontium?
• Singlet-triplet mixing leads to narrow intercombination lines, allowing cooling to <μK(spin forbidden 1S0-3P1 red MOT ~800nK Katori et al. Phys. Rev. Lett. 82 (6) (1998))
• This also allows high spectroscopic resolution(Same transition as above 7.6kHz)
• 1S0 ground state can make spectroscopy more simple (no optical pumping required)
• Singly charged ion Sr+ has several transitions in the visible, allowing spatially resolved diagnostics(5s 2S1/2 → 5p 2P1/2 transition is at 422nm)Rydberg & plasma physics using ultra-cold strontium
Introduction
Rydberg & plasma physics using ultra-cold strontium
Experimental apparatus
Rydberg & plasma physics using ultra-cold strontiumExperimental apparatus
• Vacuum system
• Chamber internals
• Electrodes
• Zeeman slower
• Detection systems
• Laser system
• Strontium vapour cell
The vacuum system
• The oven is heated by thermocoax heater wire to ~600°C, and the strontium beam is collimated with a nozzle.
• The oven can be isolated from the chamber with a gate valve and there is good differential pumping.
Rydberg & plasma physics using ultra-cold strontiumExperimental apparatus
Internals
• Coils wound from 1mm Kapton insulated copper wire
• Can produce a field gradient of 30Gcm-1 at 2.5A
• Mounted directly on top flange so can directly “plug” into the chamber
• No electrical connections in any optical path
Rydberg & plasma physics using ultra-cold strontiumExperimental apparatus
The electrodes
• Split ring geometry mounted onto MOT coil formers
• Blocks no optical access
• 8 independently controllable electrodes
• Can produce reasonably flat fields and also gradients
Rydberg & plasma physics using ultra-cold strontiumExperimental apparatus
Field calculations
• Field changes by <1% in central 4mm cube
Rydberg & plasma physics using ultra-cold strontiumExperimental apparatus
The Zeeman slower
6mm mild steel “yoke”
Copper former Heatsink block
Vacuum pipe
Extractioncoil
27cm
Rydberg & plasma physics using ultra-cold strontiumExperimental apparatus
Field
(Tesla)
Data with shield
Data without shieldSimulation
With Shield
Without Shield
The Zeeman slower
Rydberg & plasma physics using ultra-cold strontiumExperimental apparatus
Detection systems
• A home built photodiode for temporal fluorescence/absorption measurements
• A pixelfly qe CCD camera for taking images (controlled by LabView)
• A Hamamatsu micro-channel plate for detecting charges
Rydberg & plasma physics using ultra-cold strontiumExperimental apparatus
Laser System
-240MHz
Toptica frequency doubled
laser system at 461nm
Spectroscopy:
Locking our laser
using modified
PolSpec
Double pass at +120MHz
→ 0 MHz
(All frequencies quoted
relative to the
5s2 1S0 → 5s5p 1P1
transition in 88Sr)
Imaging:
For absorption
imaging
Double pass at +120MHz
→ 0 MHz
Zeeman SlowerDouble pass at -136MHz
→ +512 MHz
MOT beamsSingle pass at
+200MHz
→ -40 MHzRydberg & plasma physics using ultra-cold strontium
Experimental apparatus
Strontium vapour cell
0
0,1
0,2
0,3
0,4
0,5
0,6
0,7
0,8
0,9
1
-1,50E-01 -1,00E-01 -5,00E-02 0,00E+00 5,00E-02 1,00E-01 1,50E-01
Frequency (arb.)
Tra
ns
mis
sio
n
11.0 A
12.2 A
13.0 A
14.0 A
15.0 A
15.6 A
15.8 A
• Strontium must be heated, and hot strontium reacts with glass and copper.
• We have built a cell based on strontium dispensers that we use for spectroscopy and locking our 461nm laserA vapor cell based on dispensers for laser spectroscopy E. M. Bridge, J. Millen, C. S. Adams, M. P. A. Jones arXiv:0710.1245v2
• Second generation design has 100% optical thickness
Rydberg & plasma physics using ultra-cold strontiumExperimental apparatus
A magneto-optical trap for strontium
Rydberg & plasma physics using ultra-cold strontiumStrontium MOT
Our strontium MOT
Our very first strontium MOT
August 22nd 2008 (Friday, 17:30!)
Our much improved strontium MOT
October 2008
Theory
Rydberg & plasma physics using ultra-cold strontiumStrontium MOT
689nm
7.6kHz
Up to
13mins*
*Yasuda, Katori
Phys. Rev. Lett. 92, 153004 (2004)
(5s2) 1S0
461nm
32MHz
(5s5p) 1P1
620Hz
(5s4d) 1D2
0.33
(105Hz)
(5s5p) 3P2
0.67
(213Hz)
3P1
679nm
(1.4MHz)707nm
(6.4MHz)
(5s6s) 3S0
3P07.6kHz
Experimental sequence
Rydberg & plasma physics using ultra-cold strontiumStrontium MOT
Controlled by LabView via FPGA cardMOT beams always on
A) B-field & slowing
light off
B) Slowing light on
C) B-field and slowing
light on
D) B-field on, slowing
light off
E) B-field & slowing
light off
Some preliminary results – MOT lifetime
Rydberg & plasma physics using ultra-cold strontiumStrontium MOT
Black line I = Ipeak Blue line I = Iaverage Green line I = αIpeak
Some preliminary results – MOT atom number
Rydberg & plasma physics using ultra-cold strontiumStrontium MOT
Some preliminary results – MOT atom number
Rydberg & plasma physics using ultra-cold strontiumStrontium MOT
Conclusion
Rydberg & plasma physics using ultra-cold strontium
• We have a functioning magneto-optical trap for strontium, trapping on the primary transition at 461nm
• Preliminary number and lifetime measurements have been performed, and the apparatus is under computer control
• We are ready to take temperature and density measurements.
• Now we just need to decide on our first experiment...!
Rydberg & plasma physics using ultra-cold strontium
Dr. Matt Jones
Graham Lochead
Clémentine Javaux
(Ecole Superiure d'Optique )
Elizabeth Bridge
(Durham, now Oxford/NPL)
Sarah Mauger
(Ecole Superiure d'Optique )
Benjamin Pasquiou
(Ecole Superiure d'Optique )http://massey.dur.ac.uk/research/strontium/
strontium.html