2025 Theses Doctoral

Extending Coherence in the Frequency Domain with Four-Wave Mixing for Scalable Quantum Information

Oliver, Richard

Information stored in optical frequency modes has revolutionized and will continue enabling numerous technological capabilities in the classical regime, from detecting exoplanets using frequency combs to the high-data-rate optical fiber networks encircling the globe. Yet, despite enormous advances in matter-based quantum information science, the quantum regime of such optical frequency modes has received comparatively little attention, particularly when considering more than two frequency modes. Just as coherence plays a critical role in existing classical technologies, coherence of the quantum superpositions of frequency modes can be harnessed to achieve new technological capabilities.

As we will demonstrate, four-wave mixing, resulting from third-order optical nonlinearity, is an indispensable tool for coherently manipulating optical frequency modes in the quantum regime. In this thesis, we experimentally study three distinct applications of four-wave mixing. We achieve nonlinear soliton-effect compression of 1.2-ps pulses down to 66 fs in a low-loss 40-cm SiN waveguide; the resulting short pulses display coherent spectral broadening and can be linked with existing integrated laser sources and used to seed coherent supercontinuum generation all on one photonic chip.

Second, using Bragg-scattering four-wave mixing, we demonstrate quantum state tomography of a frequency-bin qubit under conditions of lossy propagation, proposing the use of the frequency domain for coherent and broadband quantum communication. Finally, we measure two-photon interference of three frequency modes via N-way Bragg-scattering, in which more than two pumps can mediate unitary three-dimensional transformations between the three quantum fields in the frequency domain, with applications including frequency qudits and scalable quantum advantage.