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Do Quantum Mechanical Wave Functions Exist and Can They Be Measured?

Professor David Villeneuve

Joint Attosecond Science Laboratory, National Research Council and University of Ottawa, Canada

3:30 pm Monday, 3 February 2014
EN101 Lecture Theatre (EN Building), Hawthorn.

In introductory physics courses we are taught the Copenhagen interpretation of quantum mechanics, which states that the wave function is a mathematical construct that has no basis in reality. And yet we happily calculate wave functions and use them to describe atoms and molecules. In fact quantum mechanics has been called the most accurate theory ever devised by humans. The Copenhagen interpretation does allow us to measure observables such as transition moments. If we measure the transition moments between an unknown bound-state wave function and a set of plane waves in the continuum, can we mathematically reconstruct the bound state wave function? I will show how this is possible.

High harmonic spectroscopy is a field that is only about five years old, yet holds great potential to measure the electronic structure of atoms and molecules on the femtosecond and attosecond time scales. This technique is based on the process of high harmonic generation, whereby an electron is pulled away from its parent atom by an intense laser field, and then is driven back and recombines with the ion, leading to the coherent emission of XUV photons. Since only part of the wave function that describes the electron is removed, the continuum portion interferes quantum mechanically with the bound portion, much like light does in a Michelson interferometer. It is this interference process that enables us to visualize a single molecular orbital wave function [1].  I will also briefly describe applications of high harmonic spectroscopy in the study of molecular dynamics of Br2 [2] and NO2 [3] molecules.

[1] J. Itatani, J. Levesque, D. Zeidler, H. Niikura, H. Pépin, J. C. Kieffer, P. B. Corkum and D. M. Villeneuve, Tomographic imaging of molecular orbitals, Nature (London) 432, 867-871 (2004).
[2] H. J. Worner, J. B. Bertrand, D. V. Kartashov, P. B. Corkum and D. M. Villeneuve, Following a chemical reaction using high-harmonic spectroscopy, Nature (London) 466, 604 (2010).
[3] H. J. Wörner, J. B. Bertrand, B. Fabre, J. Higuet, H. Ruf, A. Dubrouil, S. Patchkovskii, M. Spanner, Y. Mairesse, V. Blanchet, E. Mével, E. Constant, P. B. Corkum, and D. M. Villeneuve, Conical Intersection Dynamics in NO2 Probed by Homodyne High-Harmonic Spectroscopy, Science 334, 208 (2011).

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