Complete Excitation of Discrete Quantum Systems by Single Free Electrons

TL;DR

This paper demonstrates that single free electrons can fully excite discrete quantum systems with 100% probability under specific conditions, revealing nonlinear, recoil effects, and potential for controlled quantum excitations.

Contribution

It introduces a quantum theoretical framework showing complete excitation of two-level systems by single electrons, highlighting conditions for maximum excitation and recoil effects.

Findings

Maximum excitation probability of 100% achieved

Recoil effects significant near transition threshold

Excitation probability independent of electron wave function

Abstract

We reveal a wealth of nonlinear and recoil effects in the interaction between individual low-energy electrons and samples comprising a discrete number of states. Adopting a quantum theoretical description of combined free-electron and two-level systems, we find a maximum achievable excitation probability of $100\%$, which requires specific conditions relating to the coupling strength and the transition symmetry, as we illustrate through calculations for dipolar and quadrupolar modes. Strong recoil effects are observed when the kinetic energy of the probe lies close to the transition threshold, although the associated probability remains independent of the electron wave function even when fully accounting for nonlinear interactions with arbitrarily complex multilevel samples. Our work reveals the potential of free electrons to control localized excitations and delineates the boundaries of such control.