QUANTUM INFORMATION PROCESSING WITH FREQUENCY-BIN QUDITS

Encoding quantum information in narrow, equispaced frequency bins has emerged as a novel scheme for photonic quantum information processing (QIP) due to its inherent high-dimensionality and compatibility with dense spectral multiplexing networks. Generation and distribution of such state, commonly known as biphoton frequency combs (BFCs), have been widely demonstrated over fiber- and chip-compatible platforms, while the processing side is relatively underdeveloped. In this dissertation, we focus on the realization of the quantum frequency processor, a photonic device comprised of an alternating sequence of electro-optic phase modulators and Fourier-transform pulse shapers, capable of processing BFCs in a parallel and low-noise fashion. Utilizing standard telecommunication components, we experimentally complete the universal gate set required for scalable quantum computing, including a high-fidelity Hadamard gate and a coincidence-basis controlled-NOT gate. High-dimensional quantum operations are also explored on our device, where we implement the first frequency-bin tritter, a three-mode extension of the Hadamard gate. Moreover, we exploit the natural parallelizability of the system and implement tunable and independent qubit operations on co-propagating qubits. We realize frequency-bin Hong-Ou-Mandel interference with record-high visibility, as well as the first high-fidelity spectral correlation flip on two-qubit entangled states. Finally, we demonstrate essential functionalities for quantum networking, including arbitrary single-qubit rotations, and for the first time, a frequency-domain Bell-state analyzer.

Each of these demonstrations represents a primitive but essential function in frequency domain QIP, with the potential of scaling up such fundamental systems into larger processors thanks to ongoing efforts in integrated photonics design. Such large-scale integrated processors would then be well positioned for the application such as interconnecting matter qubits with mismatched frequencies and various quantum communication protocols based on frequency-bin encoding.