Encoding a qubit in a trapped-ion mechanical oscillator
Encoding a qubit in a trapped-ion mechanical oscillator
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DOI：
10.1038/s41586-019-0960-6
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发表时间：
2019-02-28
期刊：
影响因子：
64.8
通讯作者：
Home, J. P.
中科院分区：
文献类型：
--
作者：
Fluhmann, C.;Nguyen, T. L.;Home, J. P.
量子计算机的稳定运行将依赖于纠错，其中单个量子比特的信息冗余地存储在更大系统的希尔伯特空间中。这种编码的量子位通常基于许多物理量子位的阵列，但也可以使用单个高维量子系统来实现，例如谐振子（1-3）。在这样的系统中，已经基于位置本征态的周期性间隔叠加设计了强大的编码（4-6）。人们已经提出了各种各样的建议来实现这种状态的近似，但迄今为止这些建议仍然遥不可及（7-11）。在这里，我们使用单个捕获的Ca-40（+）离子的谐波运动的位移压缩态的叠加来展示这样的编码量子位，通过耦合到辅助内态量子位来控制和测量机械振荡器（12）。我们准备和重建逻辑状态的平均平方保真度为87.3 +/-0.7%.Also，我们展示了一个通用的逻辑单量子位门集，我们使用过程层析成像分析。对于泡利门，我们达到了大约97%的过程并行性，而对于连续旋转，我们使用门隐形传态，实现了大约89%的并行性。这种控制方法为探索连续变量误差校正以及使用离散和连续变量的混合量子信息方案开辟了一条道路。代码状态在量子传感中也有直接的应用，允许同时测量位置和动量的小位移（14，15）。
The stable operation of quantum computers will rely on error correction, in which single quantum bits of information are stored redundantly in the Hilbert space of a larger system. Such encoded qubits are commonly based on arrays of many physical qubits, but can also be realized using a single higher-dimensional quantum system, such as a harmonic oscillator(1-3). In such a system, a powerful encoding has been devised based on periodically spaced superpositions of position eigenstates(4-6). Various proposals have been made for realizing approximations to such states, but these have thus far remained out of reach(7-11). Here we demonstrate such an encoded qubit using a superposition of displaced squeezed states of the harmonic motion of a single trapped Ca-40(+) ion, controlling and measuring the mechanical oscillator through coupling to an ancillary internal-state qubit(12). We prepare and reconstruct logical states with an average squared fidelity of 87.3 +/- 0.7 per cent. Also, we demonstrate a universal logical single-qubit gate set, which we analyse using process tomography. For Pauli gates we reach process fidelities of about 97 per cent, whereas for continuous rotations we use gate teleportation and achieve fidelities of approximately 89 per cent. This control method opens a route for exploring continuous variable error correction as well as hybrid quantum information schemes using both discrete and continuous variables(1)3(.) The code states also have direct applications in quantum sensing, allowing simultaneous measurement of small displacements in both position and momentum(14,15).