Attosecond physics hidden in Cherenkov radiation

TL;DR

This paper develops a quantum theoretical framework to analyze the microscopic dynamics of Cherenkov radiation, revealing attosecond-scale features and quantum effects that connect macroscopic phenomena to atomic-scale processes.

Contribution

It introduces a novel quantum approach to Cherenkov radiation, uncovering intrinsic dynamics and temporal features not captured by classical or existing quantum models.

Findings

Identification of finite photon formation length and spreading time.

Discovery of negative spreading time near the Cherenkov angle.

Proposal to measure photon emission duration to infer electron packet size.

Abstract

Cherenkov radiation of charged particles moving with superluminal velocities in transparent media is a well-studied phenomenon with a plethora of applications. Its microscopic origins can be traced to the polarization of atomic shells, characterized by time scales in the subfemtosecond range - dynamics that eludes conventional macroscopic treatment. Here we present a theoretical framework for probing the intrinsic dynamics of Cherenkov radiation, unveiling quantum features absent in classical realm and even in a fully quantum theory in momentum space. These features include a finite formation length and spreading time of the photon, the latter becoming negative nearby the Cherenkov angle, a finite flash duration tied to the size of the electron packet, along with a shift in the photon arrival time that can be either positive or negative and necessitates going beyond the far-field approximation. The calculated time scales lie in the attosecond range for the relevant parameters, thus linking this macroscopic phenomenon back to its atomic origins. Finally, we propose that by measuring the duration of the Cherenkov flash one can in principle retrieve the length of the emitting packet, deepening our understanding of quantum coherence effects in photon emission.