Cloak could conceal events
We previously reported how a team led by Professor Sir John Pendry at Imperial College, London was developing metamaterials that 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 from one that conceals objects to one that conceals events, with possible applications in improving real time control.
"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," said McCall, from the Department of Physics. "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 spacetime 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," said McCall. "So, theoretically, this person might be able to do something and you wouldn't notice!"
The immediate applications are in real time computer based control and signal processing. Co-author Dr Paul Kinsler has developed a proof of concept design using customised optical fibres. A given data channel could 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, explained: "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 arose during their calculations was to speed up the transmitted data without violating the laws of relativity. Favaro solved this by devising a material whose properties varied in both space and time, allowing the cloak to be formed.
