Spatial distributions in a cold strontium Rydberg gas Graham Lochead

Graham Lochead 09/10/12 The group Matt Jones Liz Bridge Charles Adams Daniel Sadler Danielle Boddy Christophe Vaillant James Millen

Graham Lochead 09/10/12 Rydberg states n = 5 n = 8 n = 7 n = 6 Ionization limit Properties High principal quantum number n n = 68 n = 67 n = 66 H ~ 0.1 nm n = 100 ~ 1 μ m

Graham Lochead 09/10/12 Dipole blockade Strong, tunable interactions C.L. Vaillant et al., J. Phys. B (2012) M. Saffman et al., Rev. Mod. Phys (2010)

Graham Lochead 09/10/12 Dipole blockade spatial effects A. Schwartzkopf et al., Phys. Rev. Lett. 107, (2011) Radius ( μ m) Autocorrelation Position Column density Excited state Ground state

Graham Lochead 09/10/12 Further spatial effects T. Pohl et al., Phys. Rev. Lett. 104, (2010) P. Schauß et al., arXiv: Dynamical crystallisation

Graham Lochead 09/10/12 Outline Coherent Rydberg excitation Laser stabilization CPT in cold strontium atoms Optical Bloch Equation model Two electron information State transfer Autoionization microscopy Statistical distributions

Graham Lochead 09/10/12 Dispenser cell E. M. Bridge et. al., Rev. Sci. Instrum. 80, (2009) Need atomic reference cell Problems: No vapour pressure at room temperature Strontium reacts with glass Solution: Dispenser-based cell

Graham Lochead 09/10/12 Probe/cooling laser stabilization Sub-Doppler frequency modulation spectroscopy 5s 2 5s5p 5snd λ 1 = 461 nm λ 2 = 413 nm Probe Coupling

Graham Lochead 09/10/12 Coupling laser stabilization 5s 2 5s5p 5snd λ 1 = 461 nm λ 2 = 413 nm Probe Coupling R. P. Abel et al, Appl. Phys. Lett. 94, (2009) EIT-based lock M. Fleischhauer et al, Rev. Mod. Phys. 77, 633 (2005)

Graham Lochead 09/10/12 Cold atom source Zeeman slowed atomic beam 10 7 strontium atoms at 5 mK 5 x 10 9 atoms/cm 3

Graham Lochead 09/10/12 Chamber insides R. Löw et al, arXiv: v1

Graham Lochead 09/10/12 Detecting Rydberg atoms Small signal – number resolving Large signal – average only

Graham Lochead 09/10/12 CPT spectra Coupling laser locked Probe laser frequency stepped E-field does not field ionize Sub-natural linewidth Data for n = 56

Graham Lochead 09/10/12 Optical Bloch Equations Free parameters Laser linewidths Laser detuning Amplitude scaling Fixed parameters Rabi frequencies State linewidths 5s 2 5s5p 5snd ΩpΩp ΩcΩc

Graham Lochead 09/10/12 What do two electrons allow us to do?

Graham Lochead 09/10/12 Autoionization Resonant optical ionization for l < 8 Independent of excitation W.E. Cooke et al, Phys. Rev. Lett. 40, 178 (1978)

Graham Lochead 09/10/12 Temporal information J. Millen et al, J. Phys. B (2011) Pulsed dye laser used for this experiment, ECDL for the rest

Graham Lochead 09/10/12 Spectral information J. Millen et al., Phys. Rev. Lett. 105, (2010) E. Y. Xu et al., Phys. Rev. A 35, 1138 (1987) Low Rydberg densityHigh Rydberg density Shape depends on state Multi-channel quantum defect fit

Graham Lochead 09/10/12 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

Graham Lochead 09/10/12 Lifetime analysis Δt = 100 μs Look at the decay of signal at different spectral points: A A B B Blue line: The decay of the 5s54f 1 F 3 state. 54F state 25μs 60μs

Graham Lochead 09/10/12 Including 5s54f state 13 ± 3% of the Rydberg population transferred to 5s54f state

Graham Lochead 09/10/12 Mechanism The mechanism for population transfer is cold plasma formation: l-changing collisions Black data: population transfer. Red data: spontaneous ionization. Plasma threshold Initial Rydberg # Population transferred Spontaneous ionization M. P. Robinson et. al., Phy. Rev. Lett. 85, 4466 (2000)

Graham Lochead 09/10/12 Focus coupling laser Spatial intensity variation of beam makes a difference Fewer Rydberg atoms – no plasma formation

Graham Lochead 09/10/12 Spatial information Translate a focused autoionizing beam

Graham Lochead 09/10/12 Lens setup 10 μm resolution 100 mm long

Graham Lochead 09/10/12 Rydberg spatial distribution Ground state fluorescence collected Can take distributions in both directions

Graham Lochead 09/10/12 Spatial widths: Coupling power OBE simulation Autoionizing probability

Graham Lochead 09/10/12 Spatial widths: Autoionizing power T.F. Gallagher, Rydberg Atoms

Graham Lochead 09/10/12 Detection efficiency n g : ground state density P de → 1 V : overlap volume ρ 33 : Rydberg probability C : single ion conversion ε: detector efficiency ε = 21 ± 4 %

Graham Lochead 09/10/12 Statistical information

Graham Lochead 09/10/12 Towards blockade H. Schempp et al., Phys. Rev. Lett. 104, (2010) 1P11P1 1S01S0 3P03P0 3P13P1 3P23P2 λ = 689 nm Γ = 2π x 7.5 kHz 2 nd stage cooling Blue MOT: ~ 5 mK ~ 2 x 10 9 atoms/cm 3 Red MOT: ~ 400 nK ~ 2 x atoms/cm 3 λ = 461 nm Γ = 2π x 32 MHz 1 st stage cooling n = 75

Graham Lochead 09/10/12 Electrometry Use Stark effect to alter Rydberg distribution

Graham Lochead 09/10/12 Summary Thanks for listening Coherently excite strontium atoms to Rydberg states 10 µm resolution spatial distribution Number resolving technique No interactions seen → Implement second stage cooling

Graham Lochead 09/10/12