Quantum Rabi Oscillation: A Direct Test of Field Quantization in a Cavity

TLDR

The Fourier component weights are used to determine the photon number distribution in the cavity field. Rabi oscillations of circular Rydberg atoms in a high‑Q cavity show discrete Fourier components at frequencies proportional to √n, directly evidencing field quantization and revealing nonlinear quantum features at very low field strengths.

Abstract

We have observed the Rabi oscillation of circular Rydberg atoms in the vacuum and in small coherent fields stored in a high Q cavity. The signal exhibits discrete Fourier components at frequencies proportional to the square root of successive integers. This provides direct evidence of field quantization in the cavity. The weights of the Fourier components yield the photon number distribution in the field. This investigation of the excited levels of the atom-cavity system reveals nonlinear quantum features at extremely low field strengths.