Dynamical localization in the microwave ionization of Rydberg atoms
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Dynamical localization in the microwave ionization of Rydberg atoms

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Literature seminar in physical chemistry (CHEM 545, Spring 2006) at UIUC

Literature seminar in physical chemistry (CHEM 545, Spring 2006) at UIUC

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  • Aluminum foil on a CD-ROM ionizing in a domestic microwave oven. Intro: Rydberg atoms are close to ionization threshold Correspondence principle => good for semiclassical theory Ionization behavior in microwave fields => good model for quantum chaos No well-defined adiabatic – nonadiabatic transition Anomalous diffusion rate in quantum chaos => dynamical localization Classical chaotic trajectories killed by interference with everything else The larger the path in phase space, the more likely it will die Compare with experiment. To do: Look up chemical applications of Anderson localization. Peter Wolynes.

Dynamical localization in the microwave ionization of Rydberg atoms Dynamical localization in the microwave ionization of Rydberg atoms Presentation Transcript

  • Dynamical localization in the microwave ionization of Rydberg atoms Jiahao Chen May 2, 2006 http://www.gull.us/photos/misc/cd.jpg
  • rydberg states structure of a highly-excited atom
  • What Rydberg states are
    • Loosely bound electrons, i.e. n À 1
    • Just below ionization threshold
      • Classical-like behavior
    n À 1 nucleus and core electrons 100 nm Energy continuum Rydberg states  n = 3 n = 2 n = 1 low-lying electronic states 0
  • Quantum defect in Rydberg spectra
    • In atomic units, the energy of a Rydberg state is
    • The quantum defect  l measures how much a Rydberg state resembles a hydrogenic state
      • Wide range of  l : ~ 0.001 - 3
    • Each atom and angular momentum state (Z, l ) has a different spectrum
    T. F. Gallagher, Rydberg Atoms , Cambridge Univ. Press, 2005 .
  • Bohr model of the hydrogen atom n = 3, E = -1.5 eV n = 12 E = -0.09 eV E = -9 kJ/mol E = -2 kcal/mol E = -800 cm -1 E = -20 THz n = 1 E = -13.6 eV 10 a.u. = 5.3 Å Rydberg electrons are weakly bound core electrons are tightly bound Microwave ionization involves ~ 200 photons at 10 GHz distances are to scale
  • Rydberg electrons are very sensitive to core electrons Accurate polarizabilities from Stark Effect H. Gould, T. M. Miller, Adv. At. Mol. Opt. Phys. 51 (2005), 343-361 E. L. Snow et. al. , Phys. Rev. A 71 (2005), art. no. 022510 Molecular fingerprinting J. L. Gosselin, P. M. Weber, J. Phys. Chem. A 109 (2005), 4899-4904 Electron energy/eV Intensity/a.u. Theory review: W. Clark, C. H. Greene, Rev. Mod. Phys. 71 (1999), 821-833 Electric field Energy same n, different l
  • Rydberg atoms as single-photon microwave detectors
    • Monitor Rydberg transition in 85 Rb atomic beam
    • Sensitive to record low temperature thermal radiation (67 mK – 1 K)
    M. Tada, Y. Kishimoto, K. Kominato, A. Shibata, S. Yamada, T. Haseyama, I. Ogawa, H. Funahashi, K. Yamamoto, S. Matsuki, Phys. Lett. A 349 (2006) 488-493. Photon count F /Vcm -1 3.2 4.5 6.5
  • hydrogen atom a simple classical model explains its behavior well
  • The Bayfield-Koch experiment prepare Rydberg state take atoms out of storage microwave the atoms remove electrons Detect and record Hydrogen: J. E. Bayfield, P. M. Koch, Phys. Rev. Lett. 33 (1974), 258-261. Sodium: T. W. Ducas et. al. , Phys. Rev. Lett. 35 (1975), 366-369. Rubidium: L. Sirko, M. Arndt, P. M. Koch, H. Walther, Phys. Rev. A 49 (1994), 3831-3841. Lithium: C. H. Cheng, C .Y. Lee, T. F. Gallagher, Phys. Rev. A 54 (1996), 3303-3309. T. F. Gallagher, Rydberg Atoms , Cambridge Univ. Press, 2005 . Prevents ions from recombining with electrons H: electric discharge Alkali atoms: laser ablation Interaction time ~ 10 ns microwave resonator atomic beam excitation laser, e.g. CO 2 AC oscillator ion detector, e.g. mass spectrometer anode DC bias laser resonator
  • Field ionization mechanism R* + n   ! R + + e - Combined potential Potential due to applied electric field Coulomb binding potential Classical energy of Rydberg electron position Energy
  • H is described well classically
    • One-dimensional projection (no centrifugal forces)
    • Analogous to planetary motion with periodic perturbation
    • 1-D model is an accurate approximation of full 3-D atom*
    P. M. Koch, K. A. H. van Leeuwen, Phys. Rep. 255 (1995) 289-403. *E. Persson, S. Yoshida, X. M. Tong, C. O. Reinhold, J. Burgdorfer, Phys. Rev. A 68 (2003) art. no. 063406
  • Features in phase space show nature of trajectories P. M. Koch, K. A. H. van Leeuwen, Phys. Rep. 255 (1995) 289-403.
    • KAM torus
    • quasiperiodic orbits
    • bound trajectories
    • Localized in phase space
    • Chaotic layer
    • diffusive transport
    • “ ionized trajectories”
    0   Angle Action 80 65
  • Destruction of KAM tori means more chaos
    • Strong fields destroy KAM tori
    • Less bound orbits, more unbound orbits
    • Stronger fields cause more classical ionization
    P. M. Koch, Physica D 83 (1995), 178-205. weak field strong field
  • Classical model predicts onset of anomaly P. M. Koch, Physica D 83 (1995), 178-205. Classical theory: Initial state is already chaotic Wrong scaling behavior Experiment and classical model agree well at low frequencies: Transition from regular to chaotic Negligible effect from tunneling There exists a frequency at which Rydberg H atoms ionize most easily! Experiment shows suppressed ionization threshold due to dynamical localization
  • How dynamical localization occurs
    • Paths need not propagate the same way in time, leading to different dynamical phases
    • Noise suppresses localization effect
    position time time potential O. Benson et. al. , Phys. Rev. A 51 (1995), 4862-4876. E. Persson et. al. , Phys. Rev. A 66 (2002), art. no. 043407. No noise (solid line) Noise (all others)
  • alkali metal atoms
  • How alkali atoms differ
    • Theoretically:
      • Electron correlations lead to ‘core scattering effect’
      • Ionization depends greatly on exactly how microwave field was turned on
    • Experimentally:
      • Easier to prepare atomic beam
      • Heavier, slower atoms allow longer interactions
    • Observe different ionization behavior vs. H, even for very small quantum defects
    nucleus core electrons valence Rydberg electron D. Campos, M. C. Spinel, J. Madroñero, J. Phys. A 34 (2001), 8101-8118. A. Krug, A. Buchleitner, Phys. Rev. A 66 (2002), art. no. 053416. H,  l = 0 Li,  l = 0.002129 Na,  l = 0.015543
  • Nonadiabatic ionization threshold
    • Stark effect splits degeneracies in l
    • Incremental non-adiabatic transitions
    • n  n+1 transition is rate-limiting
    P. Pillet et. al. , Phys. Rev. A 30 , (1983) 280–294. L. Perotti, Phys. Rev. A 71 , (2005) art. no. 033405. Electric field Energy same n, different l
  • Li and H data show different onsets
    • Different threshold for onset of dynamical localization
    • Alkali atoms consistently easier to ionize
    • Weak time-dependence of ionization threshold (e.g. in Rb data)
    H, calc. H, expt. Li, calc. Li, expt. A. Krug, Ph.D. thesis, 2001 , http://edoc.ub.uni-muenchen.de/archive/00000336/01/Krug_Andreas.pdf L. Perotti, Phys. Rev. A 71 , (2005) art. no. 033405. H, expt.,  = 36 GHz ,  = 4 ns H, expt.,  = 36 GHz ,  = 4 ns Rb, calc.,  = 36 GHz ,  = 4 ns Rb, calc.,  = 8.87 GHz ,  = 4 ns Rb, expt.,  = 8.87 GHz,  = 5 µs
  • Calculations for Li, Na, Rb v. H atoms A. Krug, A. Buchleitner, Phys. Rev. A 72 (2005), art. no. 061402 H, expt. #2 H, expt. #1 H, calc. H, expt. #2 Li,  l = 0.40, calc. Rb,  l = 3.13, calc. Na,  l = 1.35, calc. H, calc. Li, calc. Rb, calc. Na, calc. universal scaling/ data collapse H threshold alkali threshold chaotic field ionization
    • Alkali atoms show same threshold different from H
    • Core scattering enhances dynamical localization
  • Conclusions
    • Rydberg states are great semiclassical systems
    • Ionization behavior of H Rydberg atoms well described by classical model
      • Transition from regular to chaotic motion
    • Effect electron correlation in non-H Rydberg atoms still poorly understood
      • Core electrons in alkali atoms change onset of dynamical localization
      • Effect of angular quantum number still not well understood
  • Acknowledgments
    • Prof. Jim Lisy
    • Matt Ackerman
    • Christine Cecala
    • Jason Rodriguez
    • Prof. Todd Martínez
    • The Martínez Group
    • for valued feedback and suggestions