EIT-assisted atomic squeezing

The interaction of classical and quantized electromagnetic fields with an ensemble of atoms in an optical cavity is considered. Four fields drive a double-Λ level scheme in the atoms, consisting of a pair of Λ systems sharing the same set of lower levels. Two of the fields produce maximum coherence, $\rho_{12}\approx-1/2$, between the ground state sublevels 1 and 2. This pumping scheme involves equal intensity fields that are resonant with both the one- and two-photon transitions of the Λ system. There is no steady-state absorption of these fields, implying that the fields induce a type Electromagnetically-Induced Transparency (EIT) in the medium. An additional pair of fields interacting with the second Λ system, combined with the EIT fields, leads to squeezing of the atom spin associated with the ground state sublevels. Our method involves a new mechanism for creating steady-state spin squeezing using an optical cavity. As the cooperativity parameter C is increased, the optimal squeezing varies as $C^{-1/3}$. For experimentally accessible values of C, squeezing as large as 90% can be achieved