arXiv 1709.069522017-09quant-phphysics.atom-ph

离子阱量子比特快速量子逻辑门

Fast quantum logic gates with trapped-ion qubits

V. M. Schäfer, C. J. Ballance, K. Thirumalai, L. J. Stephenson, T. G. Ballance, A. M. Steane, D. M. Lucas

备注：: author submitted version
发表信息：: Nature 555, 75-78 (2018)
DOI：: 10.1038/nature25737

摘要：

基于单个捕获原子离子的量子比特构成了构建量子计算机的一种有前途的技术，所有基本操作都已实现，并且具有某些纠错方案所需的精度。然而，用于产生量子纠缠的基本两量子位逻辑门迄今为止总是在绝热状态下执行，其中与阱中离子的特征运动频率相比，门是慢的，给出了10 kHz量级的逻辑速度。已经有许多建议执行门快于这个自然的“速度限制”的陷阱。我们实现Steane等人的方法，其使用定制的激光脉冲：这些激光脉冲在10 ns的时间尺度上成形，以驱动离子沿着轨迹运动，所述轨迹被设计成使得门操作对光相位波动不敏感。这允许快速（MHz速率）量子逻辑，这是强大的实验误差的这一重要来源。我们证明了门时间短至480 ns的纠缠产生;这小于阱中离子的单个振荡周期，并且比在类似的钙-43超精细量子比特中测量的记忆相干时间短8个数量级。该方法的功率在中间时间尺度上是最明显的，在那里它产生的门误差比传统技术低十倍以上;例如，我们实现了保真度为99.8%的1.6 us门。以更高的激光强度为代价，更快的门是可能的。该方法只需要一个单一的振幅整形脉冲和一对来自连续波激光器的光束，并提供了无与伦比的相干性，操作精度和捕获离子量子位的光学连接性与通常与固态设备相关的亚微秒逻辑速度相结合的前景。

英文摘要：

Quantum bits based on individual trapped atomic ions constitute a promising technology for building a quantum computer, with all the elementary operations having been achieved with the necessary precision for some error-correction schemes. However, the essential two-qubit logic gate used for generating quantum entanglement has hitherto always been performed in an adiabatic regime, where the gate is slow compared with the characteristic motional frequencies of ions in the trap, giving logic speeds of order 10kHz. There have been numerous proposals for performing gates faster than this natural "speed limit" of the trap. We implement the method of Steane et al., which uses tailored laser pulses: these are shaped on 10 ns timescales to drive the ions' motion along trajectories designed such that the gate operation is insensitive to optical phase fluctuations. This permits fast (MHz-rate) quantum logic which is robust to this important source of experimental error. We demonstrate entanglement generation for gate times as short as 480ns; this is less than a single oscillation period of an ion in the trap, and 8 orders of magnitude shorter than the memory coherence time measured in similar calcium-43 hyperfine qubits. The method's power is most evident at intermediate timescales, where it yields a gate error more than ten times lower than conventional techniques; for example, we achieve a 1.6 us gate with fidelity 99.8%. Still faster gates are possible at the price of higher laser intensity. The method requires only a single amplitude-shaped pulse and one pair of beams derived from a continuous-wave laser, and offers the prospect of combining the unrivalled coherence properties, operation fidelities and optical connectivity of trapped-ion qubits with the sub-microsecond logic speeds usually associated with solid state devices.

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