Two-mode squeezing in cold atomic ensembles*

Two-mode quadrature squeezed light is a valuable resource for fundamental quantum entanglement study, quantum teleportation, and quantum metrology. In this work we demonstrate two schemes for two-mode squeezing generation; both schemes are based on two strong laser fields driving transitions in a Λ-type atomic system.

In the first part of work I will overview our theoretical proposal for generation of two-mode squeezed vacuum (TMSV) through dissipation. The two signal modes interacting with the ground-state atomic coherence interfere destructively, creating TMSV with a particular squeezing parameter. The squeezing is defined by the parameters of the medium. Once the TMSV is created it stops evolving while it propagates through the lossy atomic medium.

The second part combines theoretical and experimental research. Making use of cavity-enhanced double-Λ four-wave mixing, we report –3.6 dB of squeezing (after correcting for losses), which is a record for a cold atomic ensemble. Theoretically the system is analyzed in the Heisenberg-Langevin picture. This enables us to build an intuitive and qualitative description of the experiment. Based on agreement between our experimental and theoretical results we propose routes to further increase the squeezing strength.