Imaging the He$_2$ quantum halo state using a free electron laser

TL;DR

This paper demonstrates imaging of the He$_2$ quantum halo state's wavefunction using Coulomb explosion techniques with femtosecond laser pulses and free electron laser ionization, revealing the exponential decay of the wavefunction over large distances.

Contribution

It introduces a novel experimental approach to visualize the wavefunction of a quantum halo state using advanced ionization methods.

Findings

Measured the exponential decay of the wavefunction over 250 Å.

Determined the binding energy as 151.9 ± 13.3 neV, consistent with theoretical predictions.

Showed that Coulomb explosion imaging can visualize quantum halo states.

Abstract

We report on coulomb explosion imaging of the wavefunction of the quantum halo system He$_2$. Each atom of this system is ionized by tunnelionization in a femto second laser pulse and in a second experiment by single photon ionization employing a free electron laser. We visualize the exponential decay of the probability density of the tunneling particle over distance for over two orders of magnitude up to an internuclear distance of 250 {\AA}. By fitting the slope of the density in the tunneling regime we obtain a binding energy of 151.9 $\pm$ 13.3 neV, which is in agreement with most recent calculations.