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Ultrafast manipulation of the weakly bound helium dimer

Abstract

Controlling the interactions between atoms with external fields opened up new branches in physics ranging from strongly correlated atomic systems to ideal Bose1 and Fermi2 gases and Efimov physics3,4. Such control usually prepares samples that are stationary or evolve adiabatically in time. In contrast, in molecular physics, external ultrashort laser fields are used to create anisotropic potentials that launch ultrafast rotational wave packets and align molecules in free space5. Here we combine these two regimes of ultrafast times and low energies. We apply a short laser pulse to the helium dimer, a weakly bound and highly delocalized single bound state quantum system. The laser field locally tunes the interaction between two helium atoms, imparting an angular momentum of 2 and evoking an initially confined dissociative wave packet. We record a video of the density and phase of this wave packet as it propagates from small to large internuclear distances. At large internuclear distances, where the interaction between atoms is negligible, the wave packet is essentially free. This work paves the way for future tomography of wave-packet dynamics and provides the technique for studying exotic and otherwise hardly accessible quantum systems, such as halo and Efimov states.

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Fig. 1: Field-induced interatomic potential of He2.
Fig. 2: Temporal evolution of field-induced alignment.
Fig. 3: Time evolution of the dissociative wave packet in He2 after the laser ‘kick’.
Fig. 4: Schematic of radial response of the highly delocalized single-state helium dimer to a strong laser field (pump).

Data availability

All experimental data has been archived at the Goethe-University of Frankfurt am Main and is available upon request. Source data are provided with this paper.

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Acknowledgements

We thank B. Friedrich for inspiring this work over many years and M. Lemeshko for many helpful discussions and calculations. The experimental work was supported by Deutsche Forschungsgemeinschaft (DFG). This work used the OU Supercomputing Center for Education and Research (OSCER) at the University of Oklahoma. Q.G. and D.B. acknowledge support by the US National Science Foundation (grant no. PHY-1806259).

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M.K., H.M., J.H., S.E., S.Z., A.K., M.S., L.P.H.S. and T.J. contributed to the experiment. M.K. and R.D. analysed the experimental data. Q.G. and D.B. developed the theory. Q.G. performed the calculations. All authors contributed to the manuscript.

Corresponding authors

Correspondence to Maksim Kunitski or Reinhard Dörner.

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The authors declare no competing interests.

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Peer review information Nature Physics thanks Daniel Rolles and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

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Supplementary information

Supplementary Information

Supplementary Figs. 1–21 and Discussion.

Supplementary Video 1

The video shows the field-induced temporal evolution of the change of the probability density \(|\Psi_{\text{obs}}(\vec{R},t)|^{2}-|\Psi_{\text{GS}}(R)|^{2}\) of He2 as a \((R_{\parallel},R_{\perp})\) projection in cylindrical coordinates. \(R_{\parallel}\) and \(R_{\perp}\) are the parallel and perpendicular components of the internuclear distance vector \(\vec{R}\) with respect to the laser field polarization. Left: original experimental data. Right: the same as on the left but after applying a low-pass filter in Fourier space.

Source data

Source Data Fig. 2

Panels b and c.

Source Data Fig. 3

Panels a and b.

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Kunitski, M., Guan, Q., Maschkiwitz, H. et al. Ultrafast manipulation of the weakly bound helium dimer. Nat. Phys. 17, 174–178 (2021). https://doi.org/10.1038/s41567-020-01081-3

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