Quantum delocalization, gauge and quantum optics: The light-matter interaction in relativistic quantum information

Abstract

We revisit the interaction of a first-quantized atomic system (consisting of two charged quantum particles) with the quantum electromagnetic field, pointing out the subtleties related to the gauge nature of electromagnetism and the effect of multipole approximations. We connect the full minimalcoupling model with the typical effective models used in quantum optics and relativistic quantum information such as the Unruh-DeWitt (UDW) model and the dipole coupling approximation. We point out in what regimes different degrees of approximation are reasonable and in what cases effective models need to be refined to capture the features of the light-matter interaction. This is particularly important when considering the center of mass (COM) of the atom as a quantum system that can be delocalized over multiple trajectories. For example, we show that the simplest UDW approximation with a quantum COM fails to capture crucial Röntgen terms coupling COM and internal atomic degrees of freedom with each other and the field. Finally we show how effective dipole interaction models can be covariantly prescribed for relativistically moving atoms.

Entanglement Harvesting of Inertially Moving Unruh-DeWitt Detectors in Minkowski Spacetime

“…The UDW detector is a two-level qubit with an energy gap Ω between its ground and excited states that couples linearly to a scalar field φ. Despite its simplicity, this model captures the essential features of light-matter interaction when no angular momentum is exchanged [32]. It also allows us to straightforwardly and quantitatively model the harvesting of entanglement [1][2][3][4] from the field.…”