Studies of light-matter interaction in driven circuit quantum electrodynamics (cQED) systems

Includes bibliographical references.

PhD;2024;Instrumentation and Applied Physics.

Quantum information processing leverages the principles of quantum mechanics to process information in ways that classical systems cannot. The principle of superposition and entanglement can allow quantum computers to solve certain problems much more efficiently than classical computers. A two-level system(Qubit) coupled to a resonator is the building block for such quantum information processing and multiple quantum optics experiments. On-chip superconducting circuits are used as artificial atoms. These devices can be probed using microwave pulses when cooled down to cryo temperatures. This field of circuit quantum electrodynamics (cQED) is emerging as a leading candidate for realizing scalable quantum computers. This thesis presents a comprehensive study of superconducting qubits and their applications in quantum computing and quantum optics. The research is divided into three main parts. In the first part, we will discuss the details of a superconducting transmon-resonator system we fabricated and measured. We report experimental studies of transitions between the doubly dressed states of qubit resonator system called polariton states at varying driving powers and frequencies and show how the non-dispersive coupling of the higher levels of the qubit-resonator system modifies the polariton eigenstates. We analyse the system numerically and compare it with experimental results obtained from a driven Jaynes-Cummings model. In the second part, we explore the phenomenon of quantum synchronization and propose a method to realize a composite two-qubit oscillator using a superconducting circuit. We will delve into designing a two-qubit oscillator and creating an engineered environment using superconducting circuits. We will also present simulation results to validate the feasibility of the proposed model. Lastly, as a first step towards demonstrating a two-qubit oscillator, we will demonstrate a two-qubit system. We will discuss a two-qubit gate called the cross-resonance gate and learn how to characterize a two-qubit gate. Then, we'll talk about the measurements we performed to show the signatures of the cross-resonance interaction in our device. We will compare the experimental results with the simulation results for the device and highlight the role of thermal photons in introducing some undesirable effects.