Rydberg & plasma physics using ultra-cold strontium

1. Rydberg & plasma physics using ultra-cold strontium James Millen Supervisor: Dr. M.P.A. Jones Rydberg & plasma physics using ultra-cold strontium

2. Outline • Introduction and motivation • The strontium experiment • The strontium MOT Rydberg & plasma physics using ultra-cold strontium

3. 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 Introduction Rydberg & plasma physics using ultra-cold strontium

4. 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, Science316 705-708 Introduction Rydberg & plasma physics using ultra-cold strontium

5. 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, Science316 705-708 Introduction Rydberg & plasma physics using ultra-cold strontium

6. 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 Rydberg & plasma physics using ultra-cold strontium

7. 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) Introduction Rydberg & plasma physics using ultra-cold strontium

8. 88Sr energy level diagram 412.7nm F. Sorrentino, G. Ferrari, N. Poli, R. Drullingerand G. M. Tino arXiv:physics/0609133v1 Introduction Rydberg & plasma physics using ultra-cold strontium

9. 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) Introduction Rydberg & plasma physics using ultra-cold strontium

10. Experimental apparatus • Vacuum system • Chamber internals • Electrodes • Zeeman slower • Detection systems • Laser system • Strontium vapour cell Experimental apparatus Rydberg & plasma physics using ultra-cold strontium Rydberg & plasma physics using ultra-cold strontium

11. The vacuum system Experimental apparatus Rydberg & plasma physics using ultra-cold strontium

12. 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. Experimental apparatus Rydberg & plasma physics using ultra-cold strontium

13. 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 Experimental apparatus Rydberg & plasma physics using ultra-cold strontium

14. 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 Experimental apparatus Rydberg & plasma physics using ultra-cold strontium

15. Field calculations • Field changes by <1% in central 4mm cube Experimental apparatus Rydberg & plasma physics using ultra-cold strontium

16. The Zeeman slower 6mm mild steel “yoke” Extraction coil Vacuum pipe Copper former Heatsink block 27cm Experimental apparatus Rydberg & plasma physics using ultra-cold strontium

17. The Zeeman slower Field (Tesla) Data with shield Data without shield Simulation With Shield Without Shield Experimental apparatus Rydberg & plasma physics using ultra-cold strontium

18. 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 Experimental apparatus Rydberg & plasma physics using ultra-cold strontium

19. Laser System Spectroscopy: Locking our laser using modified PolSpec Double pass at +120MHz → 0 MHz Imaging: For absorption imaging Double pass at +120MHz → 0 MHz Double pass at -136MHz → +512 MHz Zeeman Slower Single pass at +200MHz → -40 MHz MOT beams (All frequencies quoted relative to the 5s21S0 → 5s5p 1P1 transition in 88Sr) -240MHz Toptica frequency doubled laser system at 461nm Experimental apparatus Rydberg & plasma physics using ultra-cold strontium

20. Strontium vapour cell • 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 spectroscopyE. M. Bridge, J. Millen, C. S. Adams, M. P. A. Jones arXiv:0710.1245v2 • Second generation design has 100% optical thickness Experimental apparatus Rydberg & plasma physics using ultra-cold strontium

21. A magneto-optical trap for strontium Our strontium MOT Our very first strontium MOT August 22nd 2008 (Friday, 17:30!) Our much improved strontium MOTOctober 2008 Strontium MOT Rydberg & plasma physics using ultra-cold strontium

22. Theory (5s5p) 1P1 (5s6s) 3S0 679nm (1.4MHz) 620Hz 707nm (6.4MHz) (5s4d) 1D2 0.33 (105Hz) 0.67 (213Hz) 461nm 32MHz (5s5p) 3P2 3P1 3P0 Up to 13mins* 7.6kHz 689nm 7.6kHz *Yasuda, Katori Phys. Rev. Lett. 92, 153004 (2004) (5s2) 1S0 Strontium MOT Rydberg & plasma physics using ultra-cold strontium

23. Experimental sequence Controlled by LabView via FPGA card MOT beams always on • 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 Strontium MOT Rydberg & plasma physics using ultra-cold strontium

24. Some preliminary results – MOT lifetime Black line I = Ipeak Blue line I = IaverageGreen line I = αIpeak Strontium MOT Rydberg & plasma physics using ultra-cold strontium

25. Some preliminary results – MOT atom number Strontium MOT Rydberg & plasma physics using ultra-cold strontium

26. Some preliminary results – MOT atom number Strontium MOT Rydberg & plasma physics using ultra-cold strontium

27. Conclusion • 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

28. 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 Dr. Matt Jones Graham Lochead Rydberg & plasma physics using ultra-cold strontium