The study of photon-atom interaction has a long history, even before the functioning laser was invented in 1960s. The invention of lasers and the development of laser cooling and trapping technic in 1970s and 80s have pushed forward the research of photon-atom interactions. With these modern technics, the atoms can be cooled down to near absolute zero temperature, trapped by the magnetic field to form a dense atomic cloud so called magneto-optical trap (MOT). With narrow linewidth lasers and laser-cooled atoms, the interaction between photons and atoms becomes more efficient. To further increase the interaction strength, people have successfully loaded MOT into an optical cavity, so that photons inside the cavity are bounced back and forth by the cavity mirrors and pass through the atomic cloud many times (determined by cavity Finesse) before they leak out.
In this thesis, we present several experiments of the photon-atom interaction based on two- dimensional (2D) MOT apparatus. In the first experiment, we construct a photonic quantum heat engine using electromagnetically induced transparency (EIT). We demonstrate the emission is along certain direction and has a narrow linewidth so that we call it ”work”. The emissivity of work output is 9 times greater than that of a blackbody at the same temperature, which is a unique property of the quantum heat engine. Then we turn to the study of the anti-parity-time (anti-PT) symmetry in optical four-wave mixing (FWM) process, and we demonstrate that anti-PT symmetry is inherent in the forward FWM by neglecting linear gain and loss. Besides, we observe anti-PT phase transition by tuning the parametric gain.
After that, we extend the research of nonlinear photon-atom interaction to quantum regime and demonstrate the generation of both degenerate and non-degenerate frequency entangled photon pairs (biphotons) by spontaneous FWM process. Furthermore, to get the full quantum description of the FWM process, we study the Langevin quantum theory, and give the general form of Langevin noise in 2 × 2 parametric system.
To further increase the photon-atom interaction strength, we design and build up a new appa- ratus by loading 2D MOT into an optical cavity and get the cavity enhanced optical depth (OD) up to 7600 by measuring vacuum Rabi splitting. The cavity enhanced OD is 190 times higher than that without enhancement. The cavity apparatus is an ideal platform to study the photon-atom interaction in the future.