8-Port Homodyne Detection of EIT-enhanced Cross-phase Modulation Using Broadband Signal Pulses

This thesis summarizes my work on the interactions between light and matter in the context of optical quantum information processing. I have designed and implemented a phase-sensitive detection scheme for optical-frequency electromagnetic fields, which has been used to measure $\mu$rad phase shifts on nanosecond timescales. This phase measurement was developed for the express purpose of detecting cross-phase modulation (XPM), a key ingredient in the construction of optical logic gates. I have implemented the `N-scheme', a form of XPM which exploits electromagnetically-induced transparency (EIT) and which was promised to yield `giant' optical nonlinearities sufficient for all-optical quantum information processing. Using a cloud of laser-cooled $^{85}$Rb atoms as the nonlinear medium, I present the first ever experimental study of EIT-enhanced XPM in the controversial regime of broadband signal pulses and spectrally narrow EIT windows. The results of this experiment constitute a breakdown of the original proposal for EIT-enhanced XPM. In light of these findings, I conclude with a theoretical analysis of the feasibility of using N-scheme as implemented in our lab to perform a non-demolition measurement of a single photon (a crucial step when using XPM to generate a universal optical logic gate). While possible in principle, the experimental conditions necessary to achieve a signal-to-noise ratio above unity are found to be practically unrealistic, suggesting a more sophisticated scheme is necessary.Ph.D