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Coherent quantum state transfer between two Josephson phase qubits through a resonant cavity



Mika Sillanpaa, Jae Park, Raymond Simmonds


A network of quantum-mechanical systems showing long lived phase coherence of its quantum states could be used for processing quantum information. As with classical information processing, a quantum processor requires information bits (qubits) that can be independently addressed and read-out, long term memory elements to store arbitrary quantum states, and the ability to transfer quantum information through a coherent communication bus accessible to a large number of qubits. Superconducting qubits made using microfabrication techniques are a promising candidate for the realization of a large scale quantum information processor because the fabrication process is readily scalable. Although these systems have successfully passed tests of coherent coupling for up to four qubits, communication of individual quantum states between qubits via a quantum bus has not yet been demonstrated. Here, we perform an experiment demonstrating the ability to coherently transfer quantum states between two superconducting Josephson phase qubits through a rudimentary quantum bus formed by a single, on chip, superconducting transmission line resonant cavity of length 7 mm. After preparing an initial quantum state with the first qubit, this quantum information is then stored as a non-classical photon state of the resonant cavity, then retrieved at a later time by the second qubit connected to the opposite end of the cavity. Beyond basic communication, these results suggest that a superconducting high-Q cavity could also function as a long term memory element. The basic architecture presented here is scalable, offering the possibility for the coherent communication between a large number of superconducting qubits in the near future.


Josephson-junction, quantum computing, quantum infromation, qubit, transmission line


Sillanpaa, M. , Park, J. and Simmonds, R. (2007), Coherent quantum state transfer between two Josephson phase qubits through a resonant cavity, Nature, [online], (Accessed June 12, 2024)


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Created September 26, 2007, Updated October 12, 2021