Free-Electron–Bound-Electron Resonant Interaction

Abstract

Here we present a new paradigm of free-electron-bound-electron resonant interaction. This concept is based on a recent demonstration of the optical frequency modulation of the free-electron quantum electron wave function (QEW) by an ultrafast laser beam. We assert that pulses of such QEWs correlated in their modulation phase, interact resonantly with two-level systems, inducing resonant quantum transitions when the transition energy ΔE ¼ ℏω 21 matches a harmonic of the modulation frequency ω 21 ¼ nω b. Employing this scheme for resonant cathodoluminescence and resonant EELS combines the atomic level spatial resolution of electron microscopy with the high spectral resolution of lasers.

The coherence of light is fundamentally tied to the quantum coherence of the emitting particle

“…The findings detailed below determine between the contradicting results, showing explicitly that without postselection, the wave function does not affect the power spectrum of spontaneous emission, while suggesting a new observable—spectral coherence—which explicitly depends on the wave function, and how the size and shape of the latter could be extracted from it. In this context, our findings can help promote the fast-growing field of free-electron quantum optics ( 50 , 51 ) and emphasize the effect of the electron wave function in ultrafast electron beam spectroscopy experiments ( 15 ).…”

“…Considering the outlook for using free electrons as quantum probes ( 15 , 51 , 69 ), our work paves the way toward quantum measurement of free electrons and other charged particles based on spontaneous emission. One interesting direction for extending the research is to consider light emission from low-energy (tens to hundreds of electron volts) coherent electrons ( 70 , 71 ), for which the zero-recoil approximation is no longer valid.…”

Free‐Electron Qubits

“…It is interesting to explore what information could possibly be extracted from a specimen by using a free‐electron qubit as a probe for imaging or energy loss spectroscopy. For example, attention was brought recently [ 63,64 ] to studying the interaction between a quantum electron wave packet and a two‐level system representing a qubit. Imbuing the incident electron with quantum information prior to the interaction may potentially introduce new techniques to read/write data from such systems.…”

Quantum Wave-Particle Duality in Free-Electron–Bound-Electron Interaction

“…In analogy with the interaction of a QEW with radiation, the reality of the QEW shape and its modulation features were also claimed to be manifested in an interaction with matter in a newly proposed effect of free-electron-boundelectron resonant interaction (FEBERI) [31]. Based on a simple semiclassical model it was asserted in Ref.…”

“…Based on a simple semiclassical model it was asserted in Ref. [31] that a QEW, passing in the vicinity of a two-level system (TLS) target (e.g., an atom, quantum dot, crystal color center, or trapped ion), would induce QEW size-and shape-dependent transitions in the TLS. Specifically, it was suggested that an ensemble of optical frequency modulated QEWs would excite resonantly TLS transitions if their frequency of modulation (produced by a laser of frequency ω b in a PINEM setup [17]) is a subharmonic of the TLS transition frequency:…”