Tunable quantum beam splitters for quantum manipulation of a hybrid tripartite qubit system

We demonstrated coherent control of quantum states in a tripartite system consisting of a superconducting qubit and two microscopic two-level states (TLS). An initially prepared qubit state was swept through qubit-TLS avoided crossings in the energy-level spectrum. The avoided crossings act as tunable quantum beam splitters of wave function. In an analogy to optics, the transmission coefficient of the beam splitters can be varied from zero to unity or any value in between by adjusting the rate of energy sweep. When performed within the decoherence time, consecutive crossings through the beam splitters lead to coherent quantum oscillations between the quantum states of the tripartite qubit-TLS system. This Landau-Zener-Stueckelberg interference controlled by the sweeping rate provides an alternative means to manipulate multiple qubits and demonstrates macroscopic quantum coherence.