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July 22, 2011

Space-time cloak no longer sci-fi — the ultimate "hide in plain sight"


From Hamish Johnston's July 14 physicsworld.com post: "

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.

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 is comprised of 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.

McCall said, "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." 

paper describing the cloak has been uploaded to the arXiv preprint server and the authors say it will be published in Nature, thus Gaeta and colleagues are unable to speak about the paper.


Below, the abstract of the upcoming paper.

Demonstration of temporal cloaking

Recent research has uncovered a remarkable ability to manipulate and control electromagnetic fields to produce effects such as perfect imaging and spatial cloaking. To achieve spatial cloaking, the index of refraction is manipulated to flow light from a probe around an object in such a way that a "hole" in space is created, and it remains hidden. Alternatively, it may be desirable to cloak the occurrence of an event over a finite time period, and the idea of temporal cloaking was proposed in which the dispersion of the material is manipulated in time to produce a "time hole" in the probe beam to hide the occurrence of the event from the observer. This approach is based on accelerating and slowing down the front and rear parts, respectively, of the probe beam to create a well controlled temporal gap in which the event occurs so the probe beam is not modified in any way by the event. The probe beam is then restored to its original form by the reverse manipulation of the dispersion. Here we present an experimental demonstration of temporal cloaking by applying concepts from the time-space duality between diffraction and dispersive broadening. We characterize the performance of our temporal cloak by detecting the spectral modification of a probe beam due to an optical interaction while the cloak is turned off and on and show that the event is observed when the cloak is turned off but becomes undetectable when the cloak is turned on. These results are a significant step toward the development of full spatio-temporal .

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


Free, the way we like it.

You could say (though I wouldn't) that "invisibility wants to be free."

I like that.

Of interest to me is that five years ago, one physicist predicted that Harry Potter-style invisibility cloaks were "10 years away."

Looks like things are right on schedule.

July 22, 2011 at 04:01 PM | Permalink


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I don't see much in this story.

Posted by: 6.02*10^23 | Jul 23, 2011 12:44:01 PM

But where's the note? You know. The one that says, "Before your father died, he left this in my possession. Use it wisely."

Posted by: Becs | Jul 22, 2011 5:23:13 PM

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