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Demonstration of temporal cloaking - How to use "time holes" to make events disappear →

By KATIE DRUMMOND  l  Wired Jan.4, 2012

Soldiers could one day conduct covert operations in complete secrecy, now that Pentagon-backed physicists have figured out how to mask entire events by distorting light.

A team at Cornell University, with support from Darpa, the Pentagon’s out-there research arm, managed to hide an event for 40 picoseconds (those are trillionths of seconds, if you’re counting). They’ve published their groundbreaking research in this week’s edition of the journal Nature.

A 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 the object 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 has been proposed in which the dispersion of the material is manipulated in time, producing a ‘time hole’ in the probe beam to hide the occurrence of the event from the observer. This approach is based on accelerating the front part of a probe light beam and slowing down its rear part to create a well controlled temporal gap—inside which an event occurs—such that 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 in an optical fibre-based system by applying concepts from the space–time 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 and show that the amplitude of the event (at the picosecond timescale) is reduced by more than an order of magnitude when the cloak is turned on.

This is the first time that scientists have succeeded in masking an event, though research teams have in recent years made remarkable strides in cloaking objects. Researchers at the University of Texas, Dallas, last year harnessed the mirage effect to make objects vanish. And in 2010, physicists at the University of St. Andrews made leaps towards using metamaterials to trick human eyes into not seeing what was right in front of them.

Masking an object entails bending light around that object. If the light doesn’t actually hit an object, then that object won’t be visible to the human eye.

Where events are concerned, concealment relies on changing the speed of light. Light that’s emitted from actions, as they happen, is what allows us to see those actions happen. Usually, that light comes in a constant flow. What Cornell researchers did, in simple terms, is tweak that ongoing flow of light — just for a mere iota of time — so that an event could transpire without being observable.

The entire experiment occurred inside a fiber optics cable. Researchers passed a beam of green light down the cable, and had it move through a lens that split the light into two frequencies, one moving slowly and the other faster. As that was happening, they shot a red laser through the beams. Since the laser “shooting” occurred during a teeny, tiny time gap, it was imperceptible.

Sure, the team’s got a ways to go before they’re able to mask 30 seconds of action, let alone several minutes. But the research certainly opens up new possibilities. For one, masking super-quick events, like those that occur with data transmission, could help conceal covert computer operations.

In the words of Nature editors, the research marks “a significant step towards full spatio-temporal cloaking.” But it could be decades before military personnel will basically be able to zap history, as it happens: According to Cornell scientists, it’d take a machine 18,600 miles long to produce a time mask that lasts a single second.

TAGS: SCIENCE OH **** 15 notes | Jan 6, 2012 | Permalink
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