We've all heard of invisibility cloaks that can (theoretically) hide objects. But a team of researchers from Purdue University have now built a time cloak that allows them to hide events.
While invisibility cloaks make events disappear in sight, a time cloak makes an event disappear in time.To do that, the researchers have used laser light of two frequencies to send photons down a single fibre. One of the lasers is tuned in such a way to to effectively cloaks the other — which means you can only read the information on the second if you know how to look for it. New Scientist explains:
Imagine a row of cars speeding along a road slowing down in concert to create brief paths for pedestrians to safely cross. When the cars that let the pedestrians cross ahead of them speed up and re-join the rest of the traffic, no one can tell there was ever a gap in the flow — the pedestrians' presence has been cloaked. In the same way, photons' paths can be tweaked to create brief gaps where information can safely hide.
It's not the first time events have ever been cloaked — but it is the first time that they have been cloaked in a way that allows people in the know to see them if they need to. In the past, they have been so well cloaked that they have actually... disappeared forever. Now, this cloak has been shown to work for communication, successfully being used to deliver messages and even resisting external attempts to scramble the information contained within. The findings are published in Optica.
And if you think that it sounds promising for covert communication, you're not alone. "With this new device, we don't just limit ourselves to thinking about cloaks as a way of preventing somebody from getting information, but also as a way to enable communication," says Joseph Lukens, one of the researchers, told New Scientist. "One guy sees nothing, the other guy sees everything." [Optica via New Scientist]