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‘Invisibility Cloak’ Become Reality? The Future Is Now: The Invisibility Cloak Exists!

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‘Space-time cloak’ to conceal events revealed in new study. Scientists have developed a recipe for manipulating the speed of light as it passes over an object, making it theoretically possible to ‘cloak‘ the object’s movement so that an observer doesn’t notice, according to a paper in the Journal of Optics.The study, by researchers from Imperial College London, involves a new class of materials called metamaterials, which can be artificially engineered to distort light or sound waves. With conventional materials, light typically travels along a straight line, but with metamaterials, scientists can exploit a wealth of additional flexibility to create undetectable blind spots. By deflecting certain parts of the electromagnetic spectrum, an image can be altered or made to look like it has disappeared. Previously, a team led by Professor Sir John Pendry at Imperial College London showed that metamaterials could be used to make an optical invisibility cloak. Now, a team led by Professor Martin McCall has mathematically extended the idea of a cloak that conceals objects to one that conceals events.“Light normally slows down as it enters a material, but it is theoretically possible to manipulate the light rays so

that some parts speed up and others slow down,” says McCall, from the Department of Physics at Imperial College London. When light is ‘opened up’ in this way, rather than being curved in space, the leading half of the light speeds up and arrives before an event, whilst the trailing half is made to lag behind and arrives too late. The result is that for a brief period the event is not illuminated, and escapes detection. Once the concealed passage has been used, the cloak can then be ‘closed’ seamlessly.Such a space-time cloak would open up a temporary corridor through which energy, information and matter could be manipulated or transported undetected. “If you had someone moving along the corridor, it would appear to a distant observer as if they had relocated instantaneously, creating the illusion of a Star-Trek transporter,” says McCall. “So, theoretically, this person might be able to do something and you wouldn’t notice!” While using the spacetime cloak to make people move undetected is still science fiction, there are many serious applications for the new research, which was funded by the Engineering and Physical Sciences Research Council (EPSRC) and the Leverhulme Trust. Co-author Dr Paul Kinsler developed a proof of concept design using customised optical fibres, which would enable researchers to use the event cloak in signal processing and computing. A given data channel could for example be interrupted to perform a priority calculation on a parallel channel during the cloak operation. Afterwards, it would appear to external parts of the circuit as though the original channel had processed information continuously, so as to achieve ‘interrupt-without-interrupt’. Alberto Favaro,

who also worked on the project, explains: “Imagine computer data moving down a channel to be like a highway full of cars. You want to have a pedestrian crossing without interrupting the traffic, so you slow down the cars that haven’t reached the crossing, while the cars that are at or beyond the crossing get sped up, which creates a gap in the middle for the pedestrian to cross. Meanwhile an observer down the road would only see a steady stream of traffic.” One issue that cropped up during their calculations was to speed up the transmitted data without violating the laws of relativity. Favaro solved this by devising a clever material whose properties varied in both space and time, allowing the cloak to be formed.”We’re sure that there are many other possibilities opened up by our introduction of the concept of the spacetime cloak,’ says McCall, “but as it’s still theoretical at this stage we still need to work out the concrete details for our proposed applications.” Metamaterials is an expanding field of science, with a vast array of potential uses, spanning defence, security, medicine, data transfer and computing. Many ordinary household devices that work using electromagnetic fields could be made more cheaply or to work at higher speeds. Metamaterials could also be used to control other types of waves as well as light, such as sound or water waves, opening up potential applications for protecting coastal or offshore installations, or even engineering buildings to withstand earthquake waves. A simple analogy of how the spacetime cloak operates is to imagine that the photons or data packets are like cars on a busy road, with a chicken attempting to cross (see basic animation below). In the animation, the field of view moves in step with

the average velocity of the cars. The leading cars speed up, and the trailing ones briefly slow down, creating a temporary gap in the traffic. The chicken can then cross through this gap, making sure to travel forward along the road as well as across it, in order to keep pace with the gap in traffic. This situation mimics what happens in the proof of principle experimental scheme that the group has proposed, which uses light signals travelling down optical fibres. After the chicken has crossed, the leading cars briefly slow, and the trailing ones briefly speed up; so that they seamlessly return to the positions they would have had without the interruption. For the outside observer, there is no evidence that a chicken has ever crossed the road, or that anything at all altered the traffic flow – their average speed is just as expected, as is their current speed, and none have unexpectedly swerved into another lane. About Imperial College London: Consistently rated amongst the world’s best universities, Imperial College London is a science-based institution with a reputation for excellence in teaching and research that attracts 14,000 students and 6,000 staff of the highest international quality. Innovative research at the College explores the interface between science, medicine, engineering and business, delivering practical solutions that improve quality of life and the environment – underpinned by a dynamic enterprise culture. Since its foundation in 1907, Imperial’s contributions to society have included the discovery of penicillin, the development of holography and the foundations of fibre optics. This commitment to the application of research for the benefit of all continues today, with current focuses including interdisciplinary collaborations to improve global health, tackle climate change, develop sustainable sources of energy and address security challenges. In 2007, Imperial College London and Imperial College Healthcare NHS Trust formed the UK’s first Academic Health Science Centre. This unique partnership aims to improve the quality of life of patients and populations by taking new discoveries and translating them into new therapies as quickly as possible.  Colin Smith Media Research Officer Imperial College London. News from:  imperial.ac.uk

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