Abstract
As with classical information processing, a quantum information processor requires bits (qubits) that can be independently addressed and read out, long-term memory elements to store arbitrary quantum states1,2, and the ability to transfer quantum information through a coherent communication bus accessible to a large number of qubits3,4. Superconducting qubits made with scalable microfabrication techniques are a promising candidate for the realization of a large-scale quantum information processor5,6,7,8,9. Although these systems have successfully passed tests of coherent coupling for up to four qubits10,11,12,13, communication of individual quantum states between superconducting qubits via a quantum bus has not yet been realized. Here, we perform an experiment demonstrating the ability to coherently transfer quantum states between two superconducting Josephson phase qubits through a quantum bus. This quantum bus is a resonant cavity formed by an open-ended superconducting transmission line of length 7 mm. After preparing an initial quantum state with the first qubit, this quantum information is transferred and stored as a nonclassical photon state of the resonant cavity, then retrieved later by the second qubit connected to the opposite end of the cavity. Beyond simple state transfer, these results suggest that a high-quality-factor superconducting cavity could also function as a useful short-term memory element. The basic architecture presented here can be expanded, offering the possibility for the coherent interaction of a large number of superconducting qubits.
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Acknowledgements
We gratefully acknowledge discussions with J. Aumentado, K. Cicak, K. Osborne, R. Schoelkopf and D. Wineland. This work was financially supported by the NIST and the DTO.
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Sillanpää, M., Park, J. & Simmonds, R. Coherent quantum state storage and transfer between two phase qubits via a resonant cavity. Nature 449, 438–442 (2007). https://doi.org/10.1038/nature06124
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DOI: https://doi.org/10.1038/nature06124
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