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“Double-slit” Experiment for Electrons

5 min 20 min. “Double-slit” Experiment for Electrons. Electrons are accelerated to 50 keV  l = 0.0055 nm Central wire is positively charged  bends electron paths so they overlap A position-sensitive detector records where they appear. << 1 electron in system at any time.

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“Double-slit” Experiment for Electrons

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  1. 5 min 20 min “Double-slit” Experiment for Electrons • Electrons are accelerated to 50 keV  l = 0.0055 nm • Central wire is positively charged  bends electron paths so they overlap • A position-sensitive detector records where they appear. • << 1 electron in system at any time [A. TONOMURA (Hitachi) --pioneered electron holography] Play Video: www.hqrd.hitachi.co.jp/em/doubleslit.cfm

  2. ICTP Triest, 8.11. 2004 • Which-Path Information, • Decoherence & Dephasing • in Macromolecule Interferometry • Markus Arndt • Institut für Experimentalphysik, Universität Wien

  3. Part A: Matter wave experiments BEC, Atom Lasers … (1995 …) Proteins ? C60 (1999) Porphyrins (2003) Na2, I2, He2-He26(1994-1996) Cold atoms (1988 …) He & H2 (1930) Neutron (1936) Electron (1927)

  4. l = h/p = 2.5 pm (c.f. C60 is ~ 1 nm across!) [A. Zeilinger (U. Vienna), 1999] Interference of larger particles • Matter-wave interference has now been demonstrated with electrons, neutrons, atoms, small molecules, BIG molecules, & biological molecules • Recent Example: Interference of C60, a.k.a. “fullerenes”, “buckyballs” Mass = (60 C)(12 g/mole) = 1.2 x 10-24 kg

  5. Short reminder: Far-Field Diffraction at a nanograting Original distribution Narrowed distribution Without v-selection With v-selection M. Arndt et al., Nature 401, 680 (1999). O. Nairz, M. Arndt, A. Zeilinger, AJP 71, 319 (2003).

  6. Matter waves of very massive objects ? • Challenges for very massive objects: •  smaller de Broglie wavelength •  tighter collimation •  smaller count rate •  high-resolution detector required, … Solutions: Slowing and Cooling: still open field of research Near-field interferometery

  7. Talbot-Lau Interferometer Visibility: Gratings: Heidenhain, Traunreut, AXAF/CHANDRA

  8. Interferometry with Porphyrins: C44H30N4 (TPP) Question: Will high interference visibility vanish with reduced symmetry of the quantum object ? ~ 2 nm

  9. Exploring higher mass & complexity C60 F48 1632 amu ! 108 atoms in a single object ! Several isomers with different symmetries Classical Expect.: V ~ 14 % Quantum model : V ~ 37 % Experiment : V > 27 % Low velocity → Vibrational Dephasing !!

  10. Quantitative decoherence experiments Thermal emission of light Collisions

  11. Decoherence by collisions:The Idea Collision generates entanglement

  12. Decoherence by collisions:Realization Various gases can be added with a well controlled pressure

  13. Fringe visibility:Exponential pressure dependence

  14. Three models lead to the same predictions forpure de Broglie experiments Bohr: Complementarity Which-path information and interference contrast are complementary Heisenberg: „microscope“ argument Random recoils wash out the interference pattern Modern language: „Entanglement“ with the environment Leads to an uncontrolled extension of the quantum system. May be regarded as a mathematical formulation of Bohr‘s view.

  15. Can collisions limit matter interferometry ? Is a virus interferometer conceivable? A „Virus Interferometer“ would not yet be limited by collisions

  16. When a quantum talks about its position … • Loss of interference due to Thermal Radiation Idea: • Warm bodies emit light • A single photon suffices to localize the emitter to within the photon‘s wavelength

  17. “Self-Localization“ due to thermal radiation Heating of C70before it enters the interferometer (up to ~ 3000 K). Hot fullerenes emit visible light (see Mitzner& Campbell) The interference contrastdecreases, with increasing temperature L. Hackermüller, K. Hornberger, B. Brezger, A. Zeilinger & M. Arndt, Nature 427, 711(2004)

  18. Interference patterns for Increasing heating laser power

  19. Interference of heated molecules Molecule fragments or ionizes (misses detector altogether) increasing temperature vanishing quantum interference

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