Entanglement of single-atom quantum bits at a distance
Entanglement of single-atom quantum bits at a distance
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DOI：
10.1038/nature06118
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发表时间：
2007-09-06
期刊：
影响因子：
64.8
通讯作者：
Monroe, C.
中科院分区：
文献类型：
--
作者：
Moehring, D. L.;Maunz, P.;Monroe, C.
量子信息科学涉及量子系统中编码的信息的存储，操纵和通信，其中叠加和纠缠现象可以提供经典可能的增强（1，2）。大规模量子信息处理器需要稳定且可寻址的量子存储器，通常以固定量子比特（qubit）的形式，以及在可能被宏观甚至地理距离分开的存储器之间传输和纠缠量子信息的手段。原子系统是优秀的量子存储器，因为适当的内部电子状态可以在很长的时间尺度上相干地存储量子比特。另一方面，光子是在远程量子比特之间分配量子信息的天然平台，因为它们能够在很小的扰动下穿越很长的距离。最近，在通过光子通道耦合原子气体的小样本方面取得了相当大的进展（2，3），包括光和原子之间的纠缠（4，5）以及远程原子系综之间纠缠特征的观察（6）（-8）。与原子集成相反，单原子量子存储器允许通过光子通道实现条件量子门，这是量子计算的关键要求。沿着这些线，单个原子与腔中的光子耦合（2，10 -12），而被捕获的原子与自由空间中的发射光子相关联（13-17）。在这里，我们展示了两个固定的单原子量子存储器的纠缠，它们相距一米。两个被捕获的原子离子各自发射一个光子，这些光子的干涉和检测表明原子量子比特的纠缠。我们通过直接测量量子比特相关性来表征纠缠对，具有近乎完美的检测效率。虽然这种纠缠方法是概率性的，但原则上它仍然适用于后续的量子操作和可扩展的量子信息应用（18-20）。
Quantum information science involves the storage, manipulation and communication of information encoded in quantum systems, where the phenomena of superposition and entanglement can provide enhancements over what is possible classically(1,2). Large-scale quantum information processors require stable and addressable quantum memories, usually in the form of fixed quantum bits ( qubits), and a means of transferring and entangling the quantum information between memories that may be separated by macroscopic or even geographic distances. Atomic systems are excellent quantum memories, because appropriate internal electronic states can coherently store qubits over very long timescales. Photons, on the other hand, are the natural platform for the distribution of quantum information between remote qubits, given their ability to traverse large distances with little perturbation. Recently, there has been considerable progress in coupling small samples of atomic gases through photonic channels(2,3), including the entanglement between light and atoms(4,5) and the observation of entanglement signatures between remotely located atomic ensembles(6) (-8). In contrast to atomic ensembles, single-atom quantum memories allow the implementation of conditional quantum gates through photonic channels2,9, a key requirement for quantum computing. Along these lines, individual atoms have been coupled to photons in cavities(2,10-12), and trapped atoms have been linked to emitted photons in free space(13-17). Here we demonstrate the entanglement of two fixed single-atom quantum memories separated by one metre. Two remotely located trapped atomic ions each emit a single photon, and the interference and detection of these photons signals the entanglement of the atomic qubits. We characterize the entangled pair by directly measuring qubit correlations with near-perfect detection efficiency. Although this entanglement method is probabilistic, it is still in principle useful for subsequent quantum operations and scalable quantum information applications(18-20).