A Radio-Frequency Synchronization System for Fiber-Optic Quantum Networks

This thesis discusses the use of a fiber optic system to synchronize GHz frequency radio-frequency signals over distances of up to 5 km and its future applications in quantum communications. The stability of the synchronization is assessed by an ‘identity gate’, where each radio-frequency signal drives a phase modulator, and the frequency profile of a continuous wave laser sent through both modulators indicates the stability of the RF signals relative to one another. Experimental results indicate that 19 GHz signals synchronized over 5.5 km drifted less than 1 ps over 30 minutes. This is superior to the radio-frequency synthesizers’ built in synchronization method and to other commonly used protocols. To illustrate an application, the system was employed in a quantum nonlocal modulation cancellation experiment. Joint spectral characterization of the biphotons shows that this synchronization scheme can be used for nodes in a quantum communications network. More specifically, possible future applications of this technology include use in a photonic quantum local area network at Oak Ridge National Laboratories.