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Blog

Space–time cloak becomes reality

By Hamish Johnston

In this month’s issue of Physics World, Martin McCall and Paul Kinsler outline plans for an “event cloak” – a device that would be perfect for the ultimate bank heist. Now, physicists in the US are the first to build one.

McCall and Kinsler are theoretical physicists at Imperial College London and their article offers a recipe for a device that allows selected events to go undetected.

Now it seems that Alexander Gaeta and colleagues at Cornell University have built a working event cloak – albeit different from the McCall and Kinsler’s proposal.

The device comprises two “split time lenses” (STLs). The first STL takes a beam of light and splits it into two parts, one that is delayed in time and the other that is advanced in time. This creates a gap in time and any event occurring within this gap cannot be detected by the beam. The second STL then does the reverse on the beam, closing the gap in time.

An easy way of understanding this process is the “stream of cars” analogy in McCall and Kinsler’s article.

Indeed, McCall told physicsworld.com “We were very pleased to see that our concept has been realized experimentally – it doesn’t quite use the same technique we proposed, but I think it can fairly claim to be the first experimental observation of the signature of a space–time cloak”.

The July issue of Physics World is devoted to the physics of invisibility and you can download a free PDF copy here.

A paper describing the cloak has been uploaded to the arXiv preprint server and the authors say it will be published in Nature. The latter means that Gaeta and colleagues are unable to speak about the paper.

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