Physics

Every Little Second Counts

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Science  11 Jul 2008:
Vol. 321, Issue 5886, pp. 176-177
DOI: 10.1126/science.321.5886.176d

Part of the appeal of nuclear magnetic resonance phenomena is that the two-level system being manipulated (nuclear spin up, or nuclear spin down) is comparatively easy to model in a quantum mechanical framework. In this context, application of a very short and strong (“hard”) electromagnetic pulse to a spin ensemble can be approximated as having an instantaneous effect—a hard pi pulse, for instance, immediately rotating the aggregate spin vector 180°. Of course, such pulses are not precisely instantaneous, and Dong et al. show that it is possible to exploit their small but still finite durations to manipulate coherence in experiments that apply many of them, one after the other, in a train. The technique substantially reduces linewidth in inhomogeneously broadened samples, most strikingly by nearly five orders of magnitude for 29Si resonances in antimony-doped silicon powder. The authors also apply the technique to 13C probing in C60 samples. — JSY

Phys. Rev. Lett. 100, 247601 (2008).

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