Quantum Interferometry and Correlated Two-Electron Wave-Packet Observation in Helium
Abstract
The concerted motion of two or more bound electrons governs atomic and molecular non-equilibrium processes and chemical reactions. It is thus a long-standing scientific dream to measure the dynamics of two bound correlated electrons in the quantum regime. Quantum wave packets were previously observed for single-active electrons on their natural attosecond timescales. However, at least two active electrons and a nucleus are required to address the quantum three-body problem. This situation is realized in the helium atom, but direct time-resolved observation of two-electron wave-packet motion remained an unaccomplished challenge. Here, we measure a 1.2-femtosecond quantum beating among low-lying doubly-excited states in helium to evidence a correlated two-electron wave packet. Our experimental method combines attosecond transient-absorption spectroscopy at unprecedented high spectral resolution (20 meV near 60 eV) with an intensity-tuneable visible laser field to couple the quantum states from the perturbative to the strong-coupling regime. This multi-dimensional transient-coupling scheme reveals an inversion of the characteristic Fano line shapes for a range of doubly-excited states. Employing Fano-type autoionization as a natural quantum interferometer, a dynamical phase shift by laser coupling to the N=2 continuum is postulated and experimentally quantified. This phase maps a transition from effectively single-active-electron to two-electron dynamics as the electron-electron interaction increases in lower-lying quantum states. In the future, such experiments will provide benchmark data for testing dynamical few-body quantum theory. They will boost our understanding of chemically and biologically important metastable electronic transition states and their dynamics on attosecond time scales.
- Publication:
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arXiv e-prints
- Pub Date:
- May 2012
- DOI:
- 10.48550/arXiv.1205.0519
- arXiv:
- arXiv:1205.0519
- Bibcode:
- 2012arXiv1205.0519O
- Keywords:
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- Physics - Atomic Physics;
- Physics - Chemical Physics;
- Physics - Optics;
- Quantum Physics
- E-Print:
- in peer review (first reports obtained, result: scientifically sound, high quality, conclusions are robust and reliable)