Entangled laser beams and quantum ghost frequency comb

This letter reports on the study of entangled laser beams, or entangled coherent states, from their generation to their nonlocal coherent behavior. Although in continuous wave operation, the entangled laser beams are able to produce comb-like correlation with 100\% contrast in distant joint photodetection. We name this comb-function quantum ghost frequency comb (QGFC). What is the cause of these periodic sharp correlations? Can we trust zero-coincidences, or anti-correlation, in the joint measurement of CW laser beams? Besides its fundamental interests, bright QGFCs make important contributions to the fields of nonlocal precision spectroscopy, positioning, and time transfer. Superior to entangled photon pairs, measurements of entangled laser beams do not rely on photon counting and can be performed over greater distance in shorter time with higher resolution and accuracy.