The ability to create and manipulate the entanglement of a large number of quantum systems lies at the heart of emerging quantum information technologies. Thus far, multipartite entanglement has been achieved using various forms of quantum bits (qubits), such as trapped ions(1, 2), photons(3), and atoms passing through microwave cavities(4). These resources have led to advancements in quantum computation5 and communication(6, 7), and in the ability to test our fundamental understanding of quantum mechanics(8-10) and precision measurements(11, 12). Over the last several years, quantum systems based on superconducting circuits have been used to entangle pairs of qubits, either directly(13-15) or through a quantum bus(16, 17), as well as demonstrating controllable coupling(18). Here, we describe a further advancement by demonstrating the coherent interaction of three directly coupled superconducting quantum systems, two phase qubits and a resonant cavity. We introduce a simple Bloch sphere-like representation to help visualize the unitary evolution of this tripartite system as it shares a single microwave photon. Through careful control and timing of the initial conditions, we can create a rich variety of entangled states. In particular, we provide evidence for a deterministic evolution of the system from a simple product state, through a tripartite W-state, into a bipartite entangled Bell-state. These experiments open the door for entanglement generation in multiparticle superconducting systems, critical for many quantum information tasks such as teleportation(7), remote state preparation(19), and quantum networks(20, 21).
Pub Type: Journals
quantum bits, phase qubits, circuit qed, tripartite, entanglement