TOWARDS LARGE-SCALE QUANTUM COMPUTING PLATFORM IN ULTRASTRONG COUPLING REGIME

Abstract

Superconducting circuit is a prime candidate towards realizing a practical quantum computer. Besides the good controllability and scalability features, it also allows us to explore an unexplored physics territory- the ultrastrong light-matter coupling/interaction (USC), where the light-matter interaction strength is comparable to the cavity and qubit frequencies. In this thesis, we present all our investigations focusing in the superconducting circuit architecture operating at the USC regime. The ultrastrong coupling naturally provides ultrafast two-qubit gates, with which we propose to construct large quantum graph codes. We are able to create cluster states within a fraction of a nanosecond by creating entanglement between any pair of qubits. To exemplify our proposal, creations of the five-qubit and Steane codes are numerically simulated. We then move on to propose parity-protected quantum memory whose coherence lifetime can be three orders of magnitude longer than conventional quantum memory in the strong light-matter coupling limit. Lastly, we study the catalytic quantum Rabi model where the system is composed of strong-ultrastrong coupling light-matter hybrid. By tuning energy gap of the qubits while keeping the ultrastrong coupling system in its ground state, we demonstrate a strong two-qubit interaction as well as an enhanced excitation transfer between the two qubits.