Quantum Information Processing With Circuit Quantum Electrodynamics

As solid artificial atoms,superconducting qubits are one of the most promising candidates to implement quantum computing due to the scalability and the stability in manipulation.By introducing cavity quantum electrodynamics(cavity QED)into the superconducting circuits to develop circuit quantum electrodynamics(cQED),one can easily control and readout qubits because the system is isolated from the external elec-tromagnetic environment.Moreover,this method offers a possibility to realize a strong coupling between the artificial atoms and the photons,thus to implement experiments in quantum optics.In this thesis,we mainly discuss the system where the transmon coupled to 3D cavity or coplanar waveguide cavity.At first,we introduce the basis concepts about the superconducting qubits,circuit quantum electrodynamics and experiment setup,measurement methods based on the cQED system.Then we study the applications of single-qubit and multi-qubit systems in quantum information processing and quantum computation.We measure the Berry's phase via the adiabatic evolution in a two-level supercon-ducting qubit system which has potential fault tolerance in quantum computing.We focus on the implemention of the superadiabatic population transfer within the nona-diabatic regime.To realize the superadiabatic procedure,we add an additional term in the Hamiltonian,introducing an auxiliary counter-diabatic field to cancel the nonadia-batic contribution in the evolution.Based on the superadiabatic procedure,we further demonstrate quantum Phase and NOT gates.These operations,which possess both of the fast and robust features,are promising for quantum information processing.We also report about operations with a four-level superconducting circuit as a two-qubit system.This straightforwardly demonstrates a potential resource to reduce the num-ber of qubits in the quantum computing.Moreover,we realize the novel Z2 semimetal bands in the superconducting quantum circuits,paving the way for quantum-simulating novel topological quantum materials.At last,we introduce two kinds of methods to couple qubits,one is the fixed ca-pacitive coupling,and anther is the quantum bus coupling.We demonstrate the iSWAP gate and the CZ gate in two capacitive coupling qubits.Then we realize the Landau-Zener-Stiicklberg interference in the two-qubit system and the tripartite qubit system.Most importantly,we propose a scheme to perform two-qubit state tomography by independently measuring the ensemble average of quantum states of two coupled su-perconducting transmon qubits.Each qubit is capacitively coupled to its own readout cavity and can be measured separately.In order to obtain the density matrix of a two-qubit state,we apply four two-qubit unitary operations to the initial state and measure the corresponding qubit states,from which the elements of the two-qubit density ma-trix can be extracted.By using this scheme we measure the entangled two qubits with high fidelity.