Microwave quantum logic gates for trapped ions

• Published in: Nature (London) Vol. 476; no. 7359; pp. 181 - 184
• Main Authors: Ospelkaus, C., Warring, U., Colombe, Y., Brown, K. R., Amini, J. M., Leibfried, D., Wineland, D. J.
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 11.08.2011; Nature Publishing Group
• Subjects: 639/766/483/481; Atoms; Classical and quantum physics: mechanics and fields; Dynamics of a particle; Electrodes; Exact sciences and technology; Geometry; Humanities and Social Sciences; Ions; letter; Magnetic fields; Methods; Microwave radiation; Microwaves; multidisciplinary; Physics; Properties; Quantum information; Quantum theory; Science; Science (multidisciplinary); Studies; United States; Trapped ions; Quantum entanglement; Microwave radiation; Atomic ions; Information processing; Logic gates; Entangled states; Quantum information; Radiofrequency; Quantum control; ns range
• ISSN: 0028-0836; 1476-4687
• DOI: 10.1038/nature10290

Ions micro-managed It is possible to manipulate trapped atomic ions coherently using laser light, but it is difficult to exert similar control with radio frequency or microwave radiation. Two groups report new approaches that enable microwave control over trapped atomic ions for quantum information processing. Ospelkaus et al . describe a device that enables microwave control, using the magnetic fields generated by electrodes integrated into a micro-fabricated ion trap. The internal quantum states of ions held in a trap can be coherently manipulated, and entangled states generated. In a second paper, Timoney et al . report an approach based on applying microwave pulses to trapped ions, which transforms them into a state isolated from outside disturbances. This technique significantly extends the coherence time of the system, decisively improving the prospects of microwave-driven ion-trap quantum information processing. 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 wavelength 4 , 5 , 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 4 , 6 , 7 , 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 3 , 11 .