A Test of Jaynes’ Neoclassical Theory: Incoherent Resonance Fluorescence from a Coherently Excited State

Abstract

There were two motivations for observing the incoherent[1] resonance fluorescence from coherently excited Rb atoms. The first was to demonstrate the quantum-electro-dynamic (QED) coherent-optical effect that the fluorescence should have maxima when the atoms are left in a state of maximum excitation and minima when the excitation is minimized[2,3]. This effect in an optically thin sample is analogous to the precession of a permanent magnetic moment driven by an external magnetic field rotating at the Larmor frequency. The second motivation was to test the semiclassical or neoclassical theory (NCT) of Jaynes, Crisp, Stroud, and co-workers[4,5]. NCT assumes that the expectation value of the dipole moment operator is an actual dipole moment which radiates according to classical electrodynamics. Thus NCT predicts a maximum fluorescence for equal admixtures of the ground and excited states and minima when the atom is closest to a pure state whether it is the excited or ground state. Whereas QED predicts maximum fluorescence for a pure excited state, NCT predicts no fluorescence. NCT’s electromagnetic field is not quantized so no zero-point fluctuations exist to give rise to spontaneous emission from a pure excited state.