Abstract
In the microscopic world, multipartite entanglement has been achieved with various types of nanometer-sized two-level systems such as trapped ions, atoms and photons. On the macroscopic scale ranging from micrometers to millimeters, recent experiments have demonstrated bipartite and tripartite entanglement for electronic quantum circuits with superconducting Josephson junctions. It remains challenging to bridge these largely different length scales by constructing hybrid quantum systems. Doing so may allow us to manipulate the entanglement of individual microscopic objects separated by macroscopically large distances in a quantum circuit. Here we report on the experimental demonstration of induced coherent interaction between two intrinsic two-level states (TLSs) formed by atomic-scale defects in a solid via a superconducting phase qubit. The tunable superconducting circuit serves as a shuttle communicating quantum information between the two microscopic TLSs. We present a detailed comparison between experiment and theory and find excellent agreement over a wide range of parameters. We then use the theoretical model to study the creation and movement of entanglement between the three components of the quantum system.
Highlights
Establishing a coherent interaction between the three subsystemsThe pulse sequence applied to the circuit is shown in figure 2
The resonance frequencies and the couplings between the qubit and the two-level states (TLSs) are denoted by ω and v, respectively
One half of the excitation remains in the qubit and the other half is transferred to TLS2, resulting in an entangled state between these subsystems
Summary
The pulse sequence applied to the circuit is shown in figure 2. A fast flux bias pulse (of rise√time 2 ns) brings it in resonance with TLS2 and keeps it there for a fixed time to perform an iSWAP-gate [25, 29]. After this gate, one half of the excitation remains in the qubit and the other half is transferred to TLS2, resulting in an entangled state between these subsystems. The advantage of the protocol used here, in comparison to, for example, just measuring the beating between the qubit and a TLS as a function of detuning, is that the visibility does not decrease with detuning but depends only on the phase difference between the qubit and TLS2 (and the dephasing processes)
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