Coherent control of quantum states is at the heart of implementing solid-state quantumprocessors and testing quantum mechanics at the macroscopic level. Despite signifi cantprogress made in recent years in controlling single-and bi-partite quantum systems, coherentcontrol of quantum wave function in multipartite systems involving artifi cial solid-state qubitshas been hampered due to the relatively short decoherence time and lack of precise controlmethods. Here we report the creation and coherent manipulation of quantum states in a tripartitequantum system, which is formed by a superconducting qubit coupled to two microscopictwo-level systems (TLSs). The avoided crossings in the system's energy-level spectrum due tothe qubit-TLS interaction act as tunable quantum beam splitters of wave functions. Our resultshows that the Landau-Zener-St ü ckelberg interference has great potential in precise control ofthe quantum states in the tripartite system.

We report the observation of quantum jumps between macroscopic quantum states in a superconductingphase qubit coupled to the two-level systems in the Josephson tunnel junction, and all key features ofquantum jumps are confirmed in the experiments. Moreover, quantum jumps can be used to calibrate suchtwo-level systems, which are believed to be one of the main decoherence sources in Josephson devices