ABSTRACT
Quantum entanglement attracts researchers for a long run as its fundamental role in quantum physics and its potential application in the quantum information processing. Energy-time entan- gled photon pairs (biphotons) with sufficient narrow bandwidth have been widely explored in the rapid-developing researches of quantum computation and quantum networks, due to their critical significance to develop the photon-atom interaction based quantum interface.
In this Thesis, we present a comprehensive study of energy-time entanglement of photons with narrow bandwidth. We first theoretically analyze four-level system and calculate the linear and nonlinear atomic responses, and also adopt Heisenberg picture to describe the biphoton generation and thoroughly investigate the biphoton temporal and spectral properties.
After describing the 2D 85Rb magneto-optical trap we work with, including magnetic field con- trol and external-cavity diode laser systems, we demonstrate the generation of narrowband bipho- tons via backward four-wave mixing (FWM). To deeply characterize the temporal and spectral properties of our biphoton sources, we propose and demonstrate a new protocol for directly measur- ing the temporal wave functions. This protocol is beyond traditional methods and requires simpler setup and less resources. These biphotons are naturally energy-time entangled because of energy conservation in the generation process. Therefore, we measure the two-photon spectral correlation and confirm the Einstein-Podolsky-Rosen energy-time entanglement, which plays an essential role in quantum communication tasks over long distances.
We further realize and explore mirrorless optical parametric oscillation (OPO) by increasing the parametric gain with the same backward FWM scheme. The system provides an ideal platform to study OPO and squeezed light in the resonant atomic medium.