Resolving multiple peaks using a sub-transit-linewidth cross-correlation resonance

Abstract

In a recent paper [L. Feng et al., Phys. Rev. Lett. 109, 233006 (2012)], we demonstrated a sub-transit-linewidth resonance based on cross correlation between optical fields in an electromagnetically induced transparency (EIT) system. Here, we investigate the ability of such resonance to resolve multiple resonance peaks. We first report the implementation of the cross-correlation resonance in a hyperfine EIT system, with a linewidth of about $1/16$ of the transit EIT width. Then, a magnetic field is applied to create multipeak EIT resonance with tunable spacing. Cross-correlation resonance with multipeaks is observed and the line shape agrees qualitatively with our numerical simulations. We find that the multipeak correlation resonance has better contrast than the corresponding EIT resonance, but with a lower signal to noise. Furthermore, this correlation resonance cannot resolve peaks with spacing close to or less than the intrinsic width, like any other resonance techniques. We analyze the origin of this limitation and make connections to the Ramsey-type subnatural spectroscopy technique. This work shows potential applications of the correlation resonance in atomic frequency standard and laser spectroscopy.