Pre-submission Thesis Presentation

In recent times nonlinear frequency conversion from microwave to optical frequencies has garnered a lot of attention. This is owing to the ease of transport and detection of gigahertz signals through optical channels and the essentially noise-free nature of the frequency conversion process. The latter attribute has been central to proposing high-fidelity classical and quantum conversion of signals between microwave and optical frequencies.

 Several promising approaches have been taken to implement coherent conversion from microwave-to-optical frequency such as micro and nano-sized hybrid electro-optomechanical devices, silicon nitride nanobeam oscillators, rare-earth-doped crystals etc... There have been several theoretical proposals of microwave-to-optical conversion in atomic systems especially with low intensity of interacting fields , but very few experimental demonstrations.  Effecting a nonlinear resonant interaction with low intensity fields in an atomic system is not feasible in traditional nonlinear optics due to the linear and nonlinear absorption near-atomic resonance.

The challenge in microwave-to-optical conversion using atom-based schemes is to devise an energy level scheme that interacts strongly with both fields and leads to a nonlinear interaction in the system. To achieve this, we have chosen a three hyperfine atomic level scheme in room temperature Rubidium atoms which is coupled with microwave and optical fields.   In particular, our study deals with novel effects in a three-level atomic system that undergoes an electromagnetically induced transparency  effect and having a hybrid interaction between optical electric dipole and microwave magnetic dipole transitions. The hybrid interaction breaks the centrosymmetry present in the atomic system. With this scheme we have demonstrated a novel three-wave mixing process in which a coherent microwave-to-optical conversion is possible.  A theoretical analysis of the three-wave mixing process shows that our system can act as a phase-dependent amplifier. A phase-dependent amplification of an optical field using microwaves is experimentally demonstrated. Further, we have done an experiment to study the explicit dependence of ground-state coherence on the phase-dependent amplifier. We envisage that our hybrid optical amplifier will serve as a good interface for the coherent transfer and amplification of classical and quantum microwave signals to optical frequencies.