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.
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Notes to editors:
1."A spacetime cloak, or a history editor" Journal of Optics 16 November 2010 Link to paper: https://fileexchange.imperial.ac.uk/files/d9fd4f2069d/McCall_jopt_final.pdf
Research carried out at Imperial College London and University of Salford. Corresponding author: Martin W McCall, Imperial College London. For full list of authors please see paper.
2. Link to basic animation of the paper and caption/credit information:
3. The Engineering and Physical Sciences Research Council (EPSRC) is the UK's main agency for funding research in engineering and physical sciences. EPSRC invests around £850 million a year in research and postgraduate training, to help the nation handle the next generation of technological change. The areas covered range from information technology to structural engineering, and mathematics to materials science. This research forms the basis for future economic development in the UK and improvements for everyone's health, lifestyle and culture. EPSRC also actively promotes public awareness of science and engineering. EPSRC works alongside other Research Councils with responsibility for other areas of research. The Research Councils work collectively on issues of common concern via research Councils UK. Website: http://www.epsrc.ac.uk
4. The Leverhulme Trust was established in 1925 under the Will of the First Viscount Leverhulme with the instruction that its resources should be used to support "scholarships for the purposes of research and education." Since that time, the Trust has provided funding for research projects, fellowships, studentships, bursaries and prizes; it operates across all the academic disciplines, the ambition being to support talented individuals as they realise their personal vision in research and professional training. With annual funding of some £50 million, the Trust is amongst the largest all-subject providers of research funding in the UK. The Trust places special weight on: the originality of the projects put to them; the significance of the proposed work; the ability to judge and take appropriate risk in the project; the removal of barriers between traditional disciplines. Website: http://www.leverhulme.ac.uk/
5. 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. Website: www.imperial.ac.uk
Journal of Optics