Spin two-axis-twisting via coherent population trapping based cavity QED

Abstract

We present a spin two-axis-twisting mechanism via coherent population trapping (CPT) based atom–photon interactions. CPT happens and the atoms are trapped in the dark state (coherent superposition of two ground states) when the ground states are resonantly coupled to a common excited state. Close to CPT, the atoms behave as two dark-state based spins, which interact with the common cavity vacuum fields. The otherwise nonexistent interaction is created between them and is identified to be responsible for the two-axis-twisting of the ground state spin. The essential difference from the previous schemes is the compatibility of the twisting spin squeezing with the resonant atom-light interaction. The CPT resonant unit serves as a kind of new ingredients for the quantum networks.