Blackbody Radiation Noise Broadening of Quantum Systems

TL;DR

This paper investigates how blackbody radiation causes a broadening of quantum system energy levels due to photon number variance, with implications for high-precision measurements like atomic clocks.

Contribution

It introduces the concept that photon number variance in blackbody radiation leads to parametric broadening of quantum energy levels, a factor previously overlooked.

Findings

Photon number variance causes energy level broadening.

Effect inversely proportional to square-root of volume.

Unlikely to affect transition linewidths in small volumes.

Abstract

Precision measurements of quantum systems often seek to probe or must account for the interaction with blackbody radiation. Over the past several decades, much attention has been given to AC Stark shifts and stimulated state transfer. For a blackbody in thermodynamic equilibrium, these two effects are determined by the expectation value of photon number in each mode of the Planck spectrum. Here, we explore how the photon number variance of an equilibrium blackbody generally leads to a parametric broadening of the energy levels of quantum systems that is inversely proportional to the square-root of the blackbody volume. We consider the the effect in two cases which are potentially highly sensitive to this broadening: Rydberg atoms and atomic clocks. We find that even in blackbody volumes as small as 1\,cm$^3$, this effect is unlikely to contribute meaningfully to transition linewidths.