Time and Frequency Division, National Institute of Standards and Technology, 325 Broadway, Boulder, Colorado 80305, USA.
Nature. 2011 Aug 10;476(7359):181-4. doi: 10.1038/nature10290.
Control over physical systems at the quantum level is important in fields as diverse as metrology, information processing, simulation and chemistry. For trapped atomic ions, the quantized motional and internal degrees of freedom can be coherently manipulated with laser light. Similar control is difficult to achieve with radio-frequency or microwave radiation: the essential coupling between internal degrees of freedom and motion requires significant field changes over the extent of the atoms' motion, but such changes are negligible at these frequencies for freely propagating fields. An exception is in the near field of microwave currents in structures smaller than the free-space wavelength, where stronger gradients can be generated. Here we first manipulate coherently (on timescales of 20 nanoseconds) the internal quantum states of ions held in a microfabricated trap. The controlling magnetic fields are generated by microwave currents in electrodes that are integrated into the trap structure. We also generate entanglement between the internal degrees of freedom of two atoms with a gate operation suitable for general quantum computation; the entangled state has a fidelity of 0.76(3), where the uncertainty denotes standard error of the mean. Our approach, which involves integrating the quantum control mechanism into the trapping device in a scalable manner, could be applied to quantum information processing, simulation and spectroscopy.
在计量学、信息处理、模拟和化学等领域，对量子水平物理系统的控制非常重要。对于被捕获的原子离子，可以用激光相干地操纵其量子运动和内部自由度。对于射频或微波辐射，类似的控制是很难实现的：内部自由度和运动之间的基本耦合需要在原子运动的范围内发生显著的场变化，但对于自由传播的场，这种变化在这些频率下可以忽略不计。一个例外是在小于自由空间波长的结构中的微波电流近场中，其中可以产生更强的梯度。在这里，我们首先在微制造的陷阱中相干地（在 20 纳秒的时间尺度上）操纵离子的内部量子态。控制磁场是通过集成到陷阱结构中的电极中的微波电流产生的。我们还通过适用于通用量子计算的门操作生成了两个原子的内部自由度之间的纠缠；纠缠态的保真度为 0.76(3)，其中不确定性表示平均值的标准误差。我们的方法涉及以可扩展的方式将量子控制机制集成到捕获设备中，可应用于量子信息处理、模拟和光谱学。
