Monday, July 25, 2016

Exceptional points

'Exceptional points' give rise to counterintuitive physical effects

No matter whether it is acoustic waves, quantum matter waves or optical waves of a laser—all kinds of waves can be in different states of oscillation, corresponding to different frequencies. Calculating these frequencies is part of the tools of the trade in theoretical physics. Recently, however, a special class of systems has caught the attention of the scientific community, forcing physicists to abandon well-established rules.

When waves are able to absorb or release energy, so-called "exceptional points" occur, around which the waves show quite peculiar behaviour: lasers switch on, even though energy is taken away from them, light is being emitted only in one particular direction, and waves which are strongly jumbled emerge from the muddle in an orderly, well-defined state. Rather than just approaching such an exceptional point, a team of researchers at TU Wien (Vienna, Austria) together with colleagues in Brazil, France, and Israel now managed to steer a system around this point, with remarkable results that have now been published in the journal Nature.

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Spinning wheel drive bands (and other drive belts) absorb and release energy, and thus can be expected to have exceptional points, which goes far in explaining issues in drive belt design problems.

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