The physics community let out a small gasp six years ago when researchers reported the first successful “spatial cloaking,” in which light is bent around an object in a way that makes it disappear from view. The new report in the journal Nature shows how they can play with something that would seem to be even harder to manipulate: the perception of time.
“We think of time in the way that other people think of space. What other people are doing in space, we can do it in time,” said Moti Fridman, a researcher at the School of Applied and Engineering Physics at Cornell University .
“I think it’s a big step forward,” said Vladimir M. Shalaev, a professor of electrical and computer engineering at Purdue University, who has worked on spatial cloaking. “It’s another example of the beauty of ‘transformational optics,’ which is behind all these ideas.”
Temporal cloaking, like spatial cloaking, is not magic. It follows all the ironclad laws of physics and is to some extent a parlor trick, albeit performed in a highly unusual parlor. Whether it will have a use isn’t known, as the hole in time created by the Cornell team lasts only 50 trillionths of a second.
“It is not enough time to steal a painting from a museum,” Fridman said, joking. He added that there might nevertheless be practical uses of the technology.
Cloaking things, either in space or in time, requires the manipulation of light. Light carries information; it bounces off objects, defining their shape and sending those details to detectors such as our eyes. If an object can prevent light from doing that, it will become invisible.
But because light travels and has speed, it also defines when something happens. The lightening and darkening that occurs when a beam of light illuminates an event marks the event in time. If something can happen and yet leave the light unperturbed, which is the essence of temporal cloaking, then the event can become as invisible as a cloaked object.
Those manipulations are possible because of man-made substances that behave in ways that natural substances don’t. The extreme bending of light that makes spatial cloaking possible requires so-called optical metamaterials made through nanotechnology. Temporal cloaking depends on special lasers and optical fibers that disperse or undisperse light in predictable ways.
In their experiment, previewed this summer in an online archive and reported in detail in Nature on Tuesday, Fridman and his collaborators sent a laser beam of light down a fiber-optic cable. At the starting end of the cable, they pulsed the beam with a second laser that changed the light from a single wavelength to a range of wavelengths, essentially different colors.