Quantum state control, entanglement, and readout of the Josephson persistent-current qubit

Quantum state control including entanglement, and readout of the Josephson persistent-current qubit, flux qubit, are reviewed. First, we mention our single-shot readout of quantum superposition state of a flux qubit by a current biased dc-SQUID. Second, we mention entangled state and vacuum Rabi oscillations of a flux-qubit LC-resonator system where qubit-resonator coupled state are controlled by a combination of microwave and DC-shift pulses, resulting in a controlling and measuring sequence analogous to atomic cavity QED. Third, we report our recent progress in high fidelity readout of a flux qubit state via Josephson bifurcation amplifier (JBA).