Nonlinear Optics with Cold Atoms

Abstract: In this talk, I will review our recent research of unconventional nonlinear optics with cold atoms. In the first part, I will describe the construction of a quantum heat engine (QHE) based on electromagnetically induced transparency (EIT). Making use of EIT-induced atomic coherence, we experimentally showed that the directional radiation output from the QHE could have a spectral brightness 9 times higher than that of a blackbody, while there is no gain within the system. These results show a violation of detailed balance and Kirchhoff’s law of thermal radiation. In the second part, I will demonstrate non-Hermitian but anti-parity-time-symmetric four-wave mixing in cold atoms without linear gain and loss. Besides the occurrence of nontrivial phase transition, efficient nonlinear conversion without phase matching has also been observed.