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the microwave field to be scanned point-by-point. Rather, a fully two-dimensional image of one com- ponent of the microwave field can be recorded in a single shot. This increases the data acquisition rate dramatically. In addition, the technique allows not only for a reconstruction of the amplitudes, but also of the phases of the microwave field components. As the atoms are truly microscopic objects, they do not distort the microwave circuit to be characte- rized, in contrast to macroscopic probe heads. The new method works for various frequencies in the gigahertz range.

The internal-state distribution of a cloud of ultracold atoms is shown in close proximity of a microchip after applying a microwave pulse. The different pictures correspond to different field components of the microwave. © Max Riedel/Pascal Böhi/Philipp Treutlein, MPQ and LMU München

Pascal Böhi, Max F. Riedel, Theodor W. Hänsch, and Philipp Treutlein: Imaging of microwave fields using ultracold atoms, In: Applied Physics Letters, Vol. 97(2010), Issue 5, August 02, 2010, Article 051101 [3 pages], DOI:10.1063/1.3470591: http://dx.doi.org/ 10.1063/1.3470591

10-07/08 :: July/August 2010

comb symmetry. When a magnetic field is applied, the system selects an unexpectedly ordered state, hazarding the consequences of having the like poles of the magnets (all south or all north) close together which is energetically unfavourable.

“A better understanding and control of such magne- tic monopoles in the honeycomb lattice will per- mit storage of far more information in these states than is the case when using conventional storage techniques that know only two states,” is how Prof. Zabel explains the significance of the experiment.

“It might look as if we‘re just playing around, but in fact this can have far-reaching consequences for magnetic logical circuits,” says Prof. Zabel. Each node point has eight possible dipole constellations – far more than with conventional storage techniques based on two states. The dipole islands in the ex- periments were three micrometres long and 0.3µm wide, but it is conceivable for them to be much smaller – up to a tiny 300nm in length.

Spin ice can be used to examine exotic properties of magnetic systems. Surprising observations have been made by physicists working with Prof. Dr. Hartmut Zabel at the Ruhr-University, Germany, using magnetic islands only micrometres in size that are placed on a periodic lattice with honey-

Image: The illustra- tion with a magnetic force microscope shows the arrangement of magnetic north poles (pale points) and south poles (dark points) on a lithographic honeycomb lattice. It is remarkable to see three north or three south poles meeting alternately at

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