Engineering coherent quantum states in superconducting systems

Recently, we have taken the first step towards creating and controlling quantum information using superconducting circuits. We have observed for the first time a coherent interaction between two superconducting atoms (quantum bits or qubits) and an LC cavity formed by a 7 mm long coplanar waveguide resonant at approximately 9 GHz. When either qubit is resonant with the cavity, we observe the vacuum Rabi mode splitting of the qubit's spectral line. In a time-domain measurement, we observe coherent vacuum Rabi oscillations between either qubit and the resonator. Using controllable shift pulses, we have shown coherent transfer of a arbitrary quantum state. We prepare the first qubit in a superposition state, then this state is transferred to the resonant cavity and then after a short time, we transfer this state into the second qubit. These experiments show that developing custom designed quantum systems on chip is possible, opening up new possibilities for studying quantum mechanics and information science