Spectrum of the cavity-QED microlaser: Quantum frequency pulling

Summary form only given. We have investigated the wave properties manifested in the first-order coherence or the spectrum of the cavity-QED microlaser by using a high-sensitive photon-counting-based heterodyne spectroscopy. The emission spectrum exhibited a linewidth broadening due to the quantum frequency pulling effect, namely the frequency pulling dependent on the intracavity atom- and photon-number intrinsic distributions, in the presence of nonzero atom-cavity detuning. We also observed a large per-atom frequency pulling (2.1 kHz maximally), enhanced by the strong atom-cavity coupling. Moreover, a stepwise change in the frequency pulling, associated with the coherent Rabi oscillations, was observed with the increased pumping over multiple thresholds.