Spatial distributions in a cold strontium Rydberg gas Graham Lochead

Graham Lochead 06/11/12 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 06/11/12 Dipole blockade Strong, tunable interactions C.L. Vaillant et al., J. Phys. B (2012) M. Saffman et al., Rev. Mod. Phys (2010)

Graham Lochead 06/11/12 Experimental dipole blockade Saturation of excitation H. Schempp et al, Phys. Rev. Lett. 104, (2010) A. Gaëtan et al, Nature Physics 5, 115 (2009) One atom Enhanced Rabi frequency Two atoms

Graham Lochead 06/11/12 Dipole blockade directions L. Isenhower et al, Phys. Rev. Lett. 104, (2010) CNOT gate operation Y. O. Dudin et al, Science 336, 887 (2012) Single photon emitter

Graham Lochead 06/11/12 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 06/11/12 Further spatial effects T. Pohl et al., Phys. Rev. Lett. 104, (2010) P. Schauß et al., arXiv: Dynamical crystallisation

Graham Lochead 06/11/12 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 06/11/12 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 06/11/12 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 06/11/12 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 06/11/12 Cold atom source Zeeman slowed atomic beam 10 7 strontium atoms at 5 mK 5 x 10 9 atoms/cm 3

Graham Lochead 06/11/12 Chamber insides R. Löw et al, arXiv: v1

Graham Lochead 06/11/12 Detecting Rydberg atoms Small signal – number resolving Large signal – average only

Graham Lochead 06/11/12 CPT spectra Coupling laser locked Probe laser frequency stepped E-field does not field ionize Sub-natural linewidth Data for n = 56

Graham Lochead 06/11/12 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 06/11/12 Why strontium? Two valence electrons

Graham Lochead 06/11/12 Autoionization Resonant optical ionization for l < 8 Independent of excitation W.E. Cooke et al, Phys. Rev. Lett. 40, 178 (1978)

Graham Lochead 06/11/12 Temporal information J. Millen et al, J. Phys. B (2011) Pulsed dye laser used for this experiment, ECDL for the rest

Graham Lochead 06/11/12 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 06/11/12 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 06/11/12 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 06/11/12 Including 5s54f state 13 ± 3% of the Rydberg population transferred to 5s54f state

Graham Lochead 06/11/12 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 06/11/12 Focus coupling laser Spatial intensity variation of beam makes a difference Fewer Rydberg atoms – no plasma formation

Graham Lochead 06/11/12 Spatial information Translate a focused autoionizing beam

Graham Lochead 06/11/12 Lens setup 10 μm resolution 100 mm long

Graham Lochead 06/11/12 Rydberg spatial distribution Ground state fluorescence collected Can take distributions in both directions

Graham Lochead 06/11/12 Spatial widths: Coupling power OBE simulation Autoionizing probability

Graham Lochead 06/11/12 Spatial widths: Autoionizing power T.F. Gallagher, Rydberg Atoms

Graham Lochead 06/11/12 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 06/11/12 Statistical information

Graham Lochead 06/11/12 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 06/11/12 Electrometry Use Stark effect to alter Rydberg distribution

Graham Lochead 06/11/12 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 06/11/12 The group Matt Jones Liz Bridge Charles Adams Daniel Sadler Danielle Boddy Christophe Vaillant James Millen

Graham Lochead 06/11/12