Microwave quantum logic gates for trapped ions

摘要

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~(1-2). 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~(2-3), 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 wavelength4'5, where stronger gradients can be generated. Here we first manipulate coherently (on time-scales 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~(4,6-8) suitable for general quantum computation~9; 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~4, simulation~(5-10) and spectroscopy~(5-11).%用激光来相干操纵被束缚的原子离子是有可能rn的，但用射频或微波辐射来施加类似的控制却rn是困难的。两个小组在本期Nature上报告的新rn方法，使研究人员能够对被束缚的原子离子施rn加微波控制，以进行量子信息处理。Ospelkausrn等人介绍了种器件，它能利用由集成到个rn用微加工方式制成的离子阱中的电极所产生的rn磁场来施加微波控制。束缚在一个阱中的离子rn的内部量子状态可被相干控制，并且产生纠缠rn状态。在另一篇论文中，Timoney等人报告了rn一种基于向被束缚的离子施加微波脉冲的方rn法，该方法可将它们转变成个与外界扰动隔rn离的状态。这种方法显著延长了体系的相干时rn间，决定性地改善了由微波驱动的离子阱量子rn信息处理的前景。