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Symmetry breaking by quantum coherence in single electron attachment

Nature Physics volume 14, pages 149–153 (2018)Cite this article

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Abstract

Quantum coherence-induced effects in atomic and molecular systems are the basis of several proposals for laser-based control of chemical reactions. So far, these rely on coherent photon beams inducing coherent reaction pathways that may interfere with one another, to achieve the desired outcome. This concept has been successfully exploited for removing the inversion symmetry in the dissociation of homonuclear diatomic molecules, but it remains to be seen if such quantum coherent effects can also be generated by the interaction of incoherent electrons with such molecules. Here we show that resonant electron attachment to H2 and the subsequent dissociation into H (n = 2) + H− is asymmetric about the inter-nuclear axis, whereas the asymmetry in D2 is far less pronounced. We explain this observation as due to attachment of a single electron resulting in a coherent superposition of two resonances of opposite parity. In addition to exemplifying a new quantum coherent process, our observation of coherent quantum dynamics involves the active participation of all three electrons and two nuclei, which could provide new tools for studying electron correlations as a means to control chemical processes, and demonstrates the role of coherent effects in electron-induced chemistry.

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Figure 1: Expected angular distribution of H− from H2.
Figure 2: Velocity slice images of H− from H2 and D− from D2 at different electron energies.
Figure 3: Schematic of the DA process at 14 eV in H2 and D2.
Figure 4: Simulated forward–backward asymmetry (η) of the angular distribution for H2 and D2.

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Acknowledgements

We thank B. Nestmann and Y. Sajeev for useful discussions. E.K. acknowledges a Marie Curie Fellowship during the course of the measurements and E.K. and V.S.P. acknowledge the Department of Atomic Energy, India for financial support during the course of the work. N.J.M. recognizes support from the European Union Framework 7 programme LASSIE Marie Curie ITN Grant Agreement 238258 and VAMDC INFRA-2008-1.2.2 Scientific Data Infrastructure. Grant Agreement number: 239108.

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Authors and Affiliations

  1. Tata Institute of Fundamental Research, Homi Bhabha Road, Colaba, Mumbai 400005, India

    E. Krishnakumar & Vaibhav S. Prabhudesai

  2. Open University, Walton Hall, Milton Keynes MK7 6AA, UK

    Nigel J. Mason

Authors
  1. E. Krishnakumar
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  2. Vaibhav S. Prabhudesai
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Contributions

E.K. and N.J.M. planned the research. E.K. built the experiment with help from N.J.M. and carried out the measurements. V.S.P. carried out the simulations and V.S.P. and E.K. interpreted the results. E.K. and V.S.P. prepared the manuscript.

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Correspondence to E. Krishnakumar.

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The authors declare no competing financial interests.

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Krishnakumar, E., Prabhudesai, V. & Mason, N. Symmetry breaking by quantum coherence in single electron attachment. Nat. Phys. 14, 149–153 (2018). https://doi.org/10.1038/nphys4289

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