Quantum Nanophotonics: Deterministic Photon-based Quantum Logic Gate By Exploiting Few-photon Nonlinearity

Photon-based quantum logic gate has substantial advantages over conventional atom-based designs as a result of a longer coherence time and an inherent compatibility with quantum communication protocol of flying qubits, photons. As a vital logic gate for universal quantum computing, the two-photon controlled-phase gate demands a few-photon nonlinearity, which historically suffers from either an indeterministic nature in the linear optics regime, or a weak nonlinearity within naturally-occurring materials in the nonlinear optics regime. It is intriguing yet challenging to deliver a logic gate design by exploiting a genuine fewphoton nonlinearity. In this dissertation, we study a particular one-dimensional quantum nanophotonic system that offers the desired few-photon nonlinearity through light-matter interactions in the quantum limit (i.e., between light quanta of photons and individual material formation of atoms). Towards this end, we study the exotic photonic trimer state generation to frst demonstrate few-photon nonlinearity. Then we report the breakdown of the non-Hermitian Hamiltonian for correlated multi-photon process to unveil the non-trivial effects of few-photon nonlinearity. Finally by exploiting such a nonlinearity, we present a deterministic two-photon controlled-phase gate proposal, and further showcase universal quantum logic gate designs in quantum nanophotonic systems