BYU Physics and Astronomy

Abstract: We develop a model that reduces quantum electrodynamics (QED) in time plus three spatial dimensions to time plus a single spatial dimension, making it is possible to numerically calculate the dynamic behavior of simple QED systems. The dimensionality is restricted in such a way as to preserve the influence of spin and angular momentum. In contrast to the S -matrix scattering approach, these calculations are not perturbative within the zero- and one-photon sector of the relevant Hilbert space. The model restricts the electron occupation number to one and the photon occupation number to zero or one. We use this model to calculate the dynamics of a so-called bare electron that dresses itself by a photon field.

Abstract: We investigated the uniformity of electron transit times for two 5-in photomultiplier tubes: the Hamamatsu R1250 and the Adit B133D01S. We focused a highly attenuated short-pulse laser on the tubes while they were mounted on a programmable stage. The stage translated the tubes relative to the incident beam so that measurements could be made with light focused at points along a grid covering the entire photocathodes. A portion of the incident light was split from the incident beam and measured and recorded by a fast photodiode. Electron transit times were measured by computing the time delay between the recorded photodiode signal and photomultiplier signal using software constant-fraction discrimination. The Hamamatsu tube exhibited a uniform timing response that varied by no more than 1.7 ns. The Adit tube was much less uniform, with transit times that varied by as much as 57 ns. The Adit response also exhibited a spatially varying double-peak structure in its response. The technique described in this paper could be usefully employed by photomultiplier tube manufacturers to characterize the performance of their products.

Abstract:

We present calibrated measurements of single-photon Thomson scattering from free electrons driven by a laser with intensity 10¹⁸  W/cm². The measurements demonstrate that individual electrons radiate with the strength of point emitters, even when their wave packets spread to the scale of the driving-laser wavelength. The result agrees with predictions of quantum electrodynamics.