Free Electrons Probe Quantum Coherence, Revealing Oscillations with Femtosecond Resolution

The ability to observe quantum coherence, a fundamental aspect of quantum mechanics, presents a significant challenge in materials science, but new research offers a promising pathway forward. H. B. Crispin and N. Talebi, working on this theoretical development, demonstrate how free electrons can probe and reveal these fleeting quantum states within individual emitters. Their analysis shows that an interaction between a free electron and an emitter initially in a superposition of states generates measurable oscillations, and crucially, these oscillations leave a distinct signature in the electron’s energy spectrum. This breakthrough establishes a method for characterizing the quantum-coherent dynamics of single emitters using electron-based techniques, potentially revolutionizing the study of quantum materials and nanoscale devices.

Talebi’s theoretical work demonstrates how free electrons can probe and reveal fleeting quantum states within individual emitters, establishing a method for characterizing their quantum-coherent dynamics using electron-based techniques.

The analysis shows that when a free electron interacts with an emitter initially in a superposition of states, measurable oscillations are generated, leaving a distinct signature in the electron’s energy spectrum. This breakthrough potentially revolutionizes the study of quantum materials and nanoscale devices.

Free Electrons Probe Bound Electron Quantum States

Recent advances in time-resolved cathodoluminescence have enabled ultrafast studies of single emitters in quantum materials, and this work develops a quantum theory modelling the dynamics of free electrons interacting with these emitters in arbitrary initial states.

The research demonstrates that a free electron can induce transient coherent oscillations in the populations of the emitter, dependent on its initial quantum state, creating a superposition of states that leads to observable oscillations in emitted light. This theoretical framework provides a means to interpret experimental data from time-resolved cathodoluminescence and offers insights into the fundamental quantum processes occurring within materials at extremely short timescales.

The approach allows for the prediction of coherent effects and establishes a pathway for controlling quantum dynamics using free electron beams, with the system exhibiting a clear signature of quantum coherence and sensitivity to the emitter’s transition frequency when prepared in a coherent superposition.

These coherence effects manifest as oscillations in the zero-loss peak of the spectral energy-loss probability, providing a means to observe and quantify these quantum phenomena. Measurements map the spectral energy-loss probability, focusing on the zero-loss peak, enabling researchers to directly observe the influence of quantum coherence on the electron energy spectrum and determine the emitter’s transition frequency with high precision.

Emitter State Controls Electron-Emitter Interactions

This research presents a theoretical framework for understanding how electrons interact with quantum emitters, revealing a surprising sensitivity to the emitter’s initial quantum state. Scientists have demonstrated that an electron can induce coherent oscillations in the populations of a quantum emitter when the system begins in a superposition of states, a phenomenon observable through changes in the electron’s energy spectrum.

The analysis shows these coherence effects manifest as oscillations in the zero-loss peak of the spectral energy-loss probability, offering a new way to probe the dynamics of individual emitters using electron-based techniques. The team’s calculations demonstrate that the duration of these coherent oscillations depends on the emitter’s transition frequency, being longer for infrared transitions compared to optical transitions.

Importantly, the strength of these oscillations is influenced by the electron’s energy, with lower energy electrons exhibiting more prominent effects, and the relative phase of the initial superposition state acting as a control parameter. By examining the electron energy spectrum, the researchers establish a clear link between the emitter’s quantum coherence and measurable changes in the energy loss probability, opening possibilities for characterizing these subtle quantum properties.