Quantum state reduction and conditional time evolution of wave-particle correlations in cavity QED.

We report measurements in cavity QED of a wave-particle correlation function which records the conditional time evolution of the field of a fraction of a photon. Detection of a photon prepares a state of well-defined phase that evolves back to equilibrium via a damped vacuum Rabi oscillation. We record the regression of the field amplitude. The recorded correlation function is nonclassical and provides an efficiency independent path to the spectrum of squeezing. Nonclassicality is observed even when the intensity fluctuations are classical. PACS numbers: 42.50.Dv, 32.80. ‐ t, 42.50.Ct The seminal work of Hanbury-Brown and Twiss [1] marks the beginning of the systematic study of the quantum fluctuations of light. Two lines of experiments are notable: those measuring correlations between pairs of photodetections (particle aspect of light) [2‐6] and squeezing experiments which measure the variance of the electromagnetic field amplitude (wave aspect of light) [7‐9]. No attempt has been made previously to draw the particle and wave aspects together by correlating a photon detection with fluctuations of the electromagnetic field amplitude. We have done this, extending the ideas of Hanbury-Brown and Twiss to record the conditional time evolution of the amplitude fluctuations of an electromagnetic wave. Measurements are made in the strong-coupling regime of cavity quantum electrodynamics (QED) [10] and exhibit the nonclassical fluctuations of light in a dramatic new way.