Superconducting qubit-based hybrid devices

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PhD; 2022; Physics

Quantum technology has potential applications in many areas of science and engineering. Recently, there has been significant progress in developing hybrid quantum devices using a superconducting qubit platform. The hybrid devices in this category combine the advantage of superconducting qubits with other degrees of freedom. Many experimental realizations of such devices have demonstrated entanglement, state preparation, and readout between multiple modes. I will present a hybrid electromechanical device consisting of a transmon-type qubit and a SiN-based mechanical resonator. The device shows a large coupling between electrical and mechanical degrees of freedom compared to the earlier demonstration in traditional optomechanics. The large coupling manifests itself in the form of LZS interference observed in the qubit spectroscopy. In addition, I will present a theoretical model to understand the three-mode hybrid system in the presence of the external drive. In such a tripartite system, we analyze the steady-state occupation of the mechanical mode to show that the sideband cooling of the mechanical mode to its ground state is achievable. The theoretical calculations here predict the experimental parameters for the optimal readout of the mechanical mode, which is also verified experimentally. In the second part of my talk, I will discuss a novel architecture to implement a fast frequency tunable qubit in a three-dimensional waveguide cavity. Control over the qubit frequency can be a valuable resource in the hybrid system consisting of superconducting qubits. We investigate the flux-dependent dynamic range, relaxation from unconfined states, and the bandwidth of the flux line. We use the fast-flux line to tune the qubit frequency and demonstrate the swap of a single excitation between cavity and qubit mode. The circuit QED setup presented here provides an alternating method to design a modular hybrid system where the components can easily be modified, added, or removed as required for a design.