Sillanpää Mika A, Park Jae I, Simmonds Raymond W
National Institute of Standards and Technology, 325 Broadway, Boulder, Colorado 80305, USA.
Nature. 2007 Sep 27;449(7161):438-42. doi: 10.1038/nature06124.
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 states, and the ability to transfer quantum information through a coherent communication bus accessible to a large number of qubits. Superconducting qubits made with scalable microfabrication techniques are a promising candidate for the realization of a large-scale quantum information processor. Although these systems have successfully passed tests of coherent coupling for up to four qubits, 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.
与经典信息处理一样，量子信息处理器需要能够独立寻址和读出的比特（量子比特）、用于存储任意量子态的长期存储元件，以及通过大量量子比特可访问的相干通信总线传输量子信息的能力。采用可扩展微纳加工技术制造的超导量子比特是实现大规模量子信息处理器的一个有前景的候选方案。尽管这些系统已成功通过了多达四个量子比特的相干耦合测试，但通过量子总线在超导量子比特之间进行单个量子态的通信尚未实现。在此，我们进行了一项实验，展示了通过量子总线在两个超导约瑟夫森相位量子比特之间相干转移量子态的能力。这个量子总线是由一条长度为7毫米的开放式超导传输线形成的谐振腔。在用第一个量子比特制备初始量子态后，这些量子信息被转移并存储为谐振腔的非经典光子态，随后由连接到腔另一端的第二个量子比特检索。除了简单的态转移，这些结果表明，高品质因数的超导腔还可以用作有用的短期存储元件。这里展示的基本架构可以扩展，为大量超导量子比特的相干相互作用提供了可能性。
