Matthias Sonnleitner
University of Innsbruck
Matthias Sonnleitner did his PhD in Innsbruck working with Helmut Ritsch and Monika Ritsch-Marte on optical forces pulling atoms towards hot objects. He then received a Schrodinger Fellowship and moved to Glasgow where he worked with Steve Barnett. A year ago he came back to Innsbruck and continues to work on subtle features in atom-light interaction.
In these exciting times where lasers control atoms with ever increasing precision it becomes necessary to remember small effects and interactions which could previously be safely neglected but may soon become measurable.
One of these effects is the Roentgen term which describes the interaction between an atom and the magnetic component of a radiation field. Its physical interpretation is that a moving electric dipole (the atom) appears to have a magnetic dipole moment in the laboratory frame such that it can interact with magnetic fields as well.
Although this Roentgen interaction is very weak it has been shown, for example, that it must be included in the calculation of emission patterns of moving atoms [Wilkens, PRA 49, 570 (1994)]. A simple extension of these calculations leads to the surprising result, that an excited two-level atom moving through vacuum appears to experience a spurious friction force in first order v/c. At first this seems to be in obvious contradiction to other calculations showing that the interaction with the vacuum does not change the velocity of an atom. Even worse, it appears to be in contradiction to the principle of relativity. It can be shown, however, that this is a side effect of the surprising appearance of E=mc^2 in non-relativistic atomic physics [MS, Trautmann, Barnett, PRL 118, 053601 (2017)].
More generally however, the Roentgen term leads to additional forces between atoms and lasers. These forces appear whenever there is some time-modulation in the atom-light coupling, for example, if the light intensity or phase is modified or if the laser frequency is detuned from the atomic transition. We will discuss the characteristics of these Roentgen forces, explore their magnitudes and several peculiar results, such as forces acting perpendicular to the propagation axis of circularly polarized laser beams as shown in the figure [MS, Barnett, EPJD 71, 336 (2017)].
Fundamental science for quantum technologies , Atom and ion trapping
