Quantum Frequency Combs and their Applications in Quantum Information Processing

We experimentally demonstrate time-frequency entangled photons with comb-like spectra via both bulk optical crystals and on-chip microring resonators and explore their characterization in both time and frequency domain using quantum state manipulation techniques. Our characterization of these quantum frequency combs involves the use of unbalanced Mach-Zehnder interferometers and electro-optic modulators for manipulation in time- and frequency-domain, respectively. By creating indistinguishable superposition states using these techniques, we are able to interfere states from various time- and frequency-bins, consequently proving time- and frequency-bin en-tanglement. Furthermore, our time-domain manipulations reveal pair-wise continuous time-energy entanglement that spans multiple frequency bins, while our utilization of electro-optic modulators to verify high-dimensional frequency-bin entanglement constitutes the proof of this phenomenon for a spontaneous four-wave mixing pro-cess. By doing so, we show the potential of these quantum frequency combs for high-dimensional quantum computing with frequency-encoded quantum states, as well as fully secure quantum communications via quantum key distribution by per-forming a nonlocal dispersion cancellation experiment. To show the potential of our entangled photons source for encoding quantum information in the frequency domain, we carry out a frequency-domain Hong-Ou-Mandel interference experiment by implementing a frequency beam splitter. Lastly, we use the high-dimensionality of our time-frequency entangled source in both time and frequency domain to implement deterministic high-dimensional controlled quantum gates, with the quantum information encoded in both the time and frequency degrees of freedom of a single photon. This novel demonstration of deterministic high-dimensional quantum gates paves the way for scalable optical quantum computation, as quantum circuits can be implemented with fewer resources and high success probability using this scheme.