Resolution enhancement of ghost imaging in atom vapor

Ghost imaging is an imaging technique in which the image of an object is revealed only in the correlation measurement between two beams of light, whereas the individual measurements contain no imaging information. Normally, the resolution of the image, which even exceeds the Rayleigh limit, is shown to be related to the transverse coherent length (l_c) of the speckle pattern. In this Letter, we demonstrate experimentally that the speckle size can be compressed by a coherent population trapping (CPT) process in atom vapor, and the resolution of GI can be greatly enhanced by the CPT process. The technique we exploit is quite efficient and robust, and it may be useful in the field of quantum and classical two-photon imaging, all-optical image processing, and quantum communication.