Nonadiabatic contributions to Bragg-regime dynamics in atomic Kapitza-Dirac scattering

TL;DR

This paper investigates how nonadiabatic effects influence the dynamics of atomic Bragg scattering in the Kapitza-Dirac regime, emphasizing the importance of including multiple off-resonant states for accurate modeling.

Contribution

It demonstrates that accurately modeling Bragg-regime scattering requires considering an increasing number of off-resonant intermediate states proportional to the square root of the field strength.

Findings

Correct Pendellösung frequencies depend on multiple off-resonant states.

Including more off-resonant states improves the accuracy of scattering phase calculations.

Nonadiabatic contributions significantly affect energy transfer in the process.

Abstract

Atomic Kapitza-Dirac Bragg regime scattering is a multiphoton process in which a neutral atom undergoes a change of momentum through an interaction with a coherent light source. When the Bragg conditions are met, the outgoing atom beams are spatially quantized. Counterpropagating lasers act as pump and probe scattering from far-off-resonant excited intermediate electronic states, leaving the atoms in the electronic ground state with quantized transverse momentum. Each nontrivial scattering event imparts transverse velocity and therefore kinetic energy to the deflected atoms through recoil. In the Bragg regime, the loss of energy in the light fields is equal to the gain of kinetic energy in the atom. Energy nonconserving intermediate states, which are described by nonadiabatic contributions, are not accounted for by first-order off-resonant states. By comparing the solutions of increasing orders of off-resonant intermediate states, it becomes clear that calculating the correct Pendell\"{o}sung frequencies and phases requires including an ever increasing number of off-resonant states in proportion to the square root of the field strength.