Resonant energy transport in aggregates of ultracold Rydberg-Atoms

Transcription

1 Resonant energy transport in aggregates of ultracold Rydberg-Atoms C.S. Hofmann, G. Günter, H. Schempp, N. Müller, O. Mülken 1, A. Blumen 1, A. Eisfeld 2, T. Amthor, and M. Weidemüller Quantum dynamics of atomic and molecular systems Ruprecht-Karls-University Heidelberg Physics Department Varenna, June 30 th :Physics Department, University of Freiburg, Freiburg, Germany 2: Max Planck Institute for the Physics of Complex Systems, Dresden, Germany Overview Introduction to ultracold Rydberg physics Resonant energy transfer in unstructured Rydberg gases Exciton transfer in Rydberg Aggregates Conclusion

2 Alkali Rydberg atoms 0 rubidium S P D F G+ hydrogen Rydberg states: Highly excited (n > 30) hydrogen-like electronic states b inding e nerg c m -1 D D1 / D2 lines (780 nm) rich internal degrees of freedom (n, l) δ = δ = δ = δ = Scalings Small binding energy n -2 (10 cm n=100) Long radiative lifetimes n 3 (1 n=100) n 5 (circular states) Orbital radius n 2 (0.5 n=100) Transition dipole moment n 2 (10 4 ea n=100) Frequency n n+1 n -3 (10 n=100) Polarizability n 7 ( ea n=100) T. F. Gallagher, Rydberg Atoms (Cambridge university Press, Cambridge, 1994)

3 Ultracold Rydberg Gases magneto-optical trap (MOT) atoms ρ ~ cm -3 T < 100 µk ultralong range interactions: - large polarizability n 7 - strong dipole interaction n 4 - strong van-der-waals forces n 11 Experimantal Setup 10 cm

4 Creation and detection of an ultracold Rydberg gas Magneto-optical trapping of 87 Rb atoms ρ = cm -3 cm T < 100 µk ns / nd 5P 3/2 780nm 5S 1/2 Creation and detection of an ultracold Rydberg gas Rydberg excitation ns / nd 480nm 5P 3/2 780nm 5S 1/2

5 Creation and detection of an ultracold Rydberg gas Sate-selective field ionization MCP Excitation schemes STIRAP 0.3 µs ns / nd 480nm 5P 3/2 780nm 5S 1/2 Rydberg Signal [arb.u.] delay [ns] 1 st sequence 2 nd sequence Deiglmayr et al., Opt.Comm. 264, 293 (2006)

6 Excitation schemes STIRAP Coherent Rydberg excitation 2 photon 2 level ns ns / nd / nd 5P 3/2 5P 3/2 5S 1/2 5S 1/2 Reetz-Lamour et al., PRL 100, (2008), Reetz-Lamour et al., NJP 10, (2008) see also: Johnson et al., PRL 100, (2008) Blockade of excitation Potential V(R) dipole interaction suppression excitation internuclear distance R ~10 5 a 0 r> r> g> r> g> g> Number of Rydberg atoms blockade radius Singer et al., PRL 93, (2004) Singer et al., JPhys B 38, 295 (2005) Reetz-Lamour et al., NJP 10, (2008) see also: Tong et al., PRL 93, (2004)

7 Resonant energy transfer processes s' 2-atom picture energy p s electric field dipole operator unstructured clouds vs micro structured aggregates Westermann et al., EPJ D 40, 37 (2006) Mülken et al., PRL 99, (2007) Overview Introduction to ultracold Rydberg physics Resonant energy transfer in unstructured Rydberg gases Exciton transfer in Rydberg Aggregates Conclusion

8 Modelling dynamics of RET in a cold gas Two atom energy transfer Atom 1 Atom 2 Pair oscillations fraction of ns atoms Interaction time (µs) Modelling dynamics of RET in a cold gas How does RET work in an unstructured gas? preparation energy transfer energy diffusion energy transfer restarts energy

9 Modelling dynamics of RET in a cold gas Complex dynamics Pair oscillations fraction of ns atoms fraction of ns atoms Interaction time (µs) Interaction time (µs) Theory vs. experiment Many-body effects and spatial variations wash out oscillation Underlying processes fully coherent! fraction of s atoms atoms 4 atoms 6 atoms 8 atoms interaction time [µs] 10 atoms number of atoms (arb. u.) 5 number of atoms (arb. u.) number of atoms (arb. u.) high density cm -3 medium density cm low density cm Westermann et al., EPJD 40, 37 (2006)

10 Energy transfer dynamics Biological systems: Rydberg aggregates: 2-level system: resonant dipole couplings between atoms nonradiative energy transfer chains with fixed pair distances tunable interaction strength! Tailored model system: excitation Controllable, coherent excitation transport! detection Overview Introduction to ultracold Rydberg physics Resonant energy transfer in unstructured Rydberg gases Exciton transfer in Rydberg Aggregates Conclusion

11 Exciton dynamics on a 1-D chain exciton transport on an ideal chain: separation between sites: R ~ µm dipole-dipole coupling:ω dd Experimental implementation: time t / hopping time excitation probablity site calculations by A. MPIPKS Exciton dynamics on a 1-D chain exciton transport under the presence of excitation traps trap site tunable trapping efficiencyγ experimental implementation: time t / hopping time excitation probablity site Γ= 0.5 Ω dd calculations by A. MPIPKS

12 Exciton dynamics on a 1-D chain exciton transport under the presence of excitation traps trap site tunable trapping efficiencyγ experimental implementation: time t / hopping time excitation probablity site Γ= 2 Ω dd calculations by A. MPIPKS Introducing spatial disorder What happens if we introduce spatial disorder? time t / hopping time excitation probablity time t / hopping time excitation probablity site no spatial disorder: σ = 0 Γ = Ω dd site spatial disorder: σ= 0.3 R Γ = Ω dd localization of excitation loss of coherence calculations by A. MPIPKS

13 Classical vs quantum transport What is the underlying nature of the exciton transport? exciton survival probability Continuous time classical random walk (CRW) Continuous time Quantum walk (CTQW) time t / hopping time CRW very different to CTQW Classical and quantum transport experimentally distinguishable! Mülken et al., PRL 99, (2007) Conclusion 1 Resonant energy transfer in ultracold Rydberg gases Good agreement of coherent many-body model with experiment in unstructured gas Exciton transport in Rydberg aggrgates under the presence of: - excitation traps - spatial disorder Classical vs quantum transport Possible experimental implementations

14 Heidelberg Rydberg team Heidelberg Rydberg-Team: C. H., G. Günter, H. Schempp, N. Müller, T. Amthor, and M. Weidemüller B. DePaola (Guest from Kansas State) Former members: C. Giese, M. Reetz-Lamour, S. Westermann, J. Deiglmayer, K. Singer Thank you for your attention