Correlated Raman photon pairs and finite-temperature quantum memory

Quantum communication technology would need a reliable quantum system for quantum information storage. Many studies of optical quantum memory involve the Raman scheme for writing and reading of optical pulses and single photons that carry quantum information. Optical quantum memory is an essential component in quantum information technology, particularly for secure long-distance quantum communication networks. Many quantum memory schemes have been proposed and demonstrated experimentally but there are limitations, especially with regard to practicality and scalability. We will discuss our work towards room temperature quantum memory which has been regarded as formidable due to the rapid decoherence and broadened absorption/emission peaks. Counter-propagating laser schemes can be applied to achieve optimal performances by overcoming these problems. This would be a step forward to realizing a practical quantum network.
We will discuss the use of Heisenberg-Langevin-Maxwell coupled equations to study quantum correlations and relative squeezing of Raman photon pairs for forward and backward propagating gemetries with arbitrary pump and control lasers using double Raman scheme. We generalized the quantum theory of stimulated Raman scattering to study the spatial-temporal dynamics of photons during storage and retrieval stages of quantum memory with all dissipative mechanisms included, such as atomic motion, collisions and radiation baths. We will discuss the effects of controllable laser pulses, velocity distribution and atomic initial conditions (like atomic frequency comb). Our study involves numerical solutions of Heisenberg-Langevin-Maxwell coupled equations generalized analytical solutions that can be used to study the quantum memory performance like storage time, efficiency and the correlations between storage and retrieval photons.