Invisibility Cloak Hides Data in a Hole in Time

A research team at Purdue has demonstrated a way to make data traveling via fiber-optic lines invisible using time travel.

Yes, that’s right—invisibility and time travel. Superhero stuff.

In a letter published in Nature, researchers described using lasers to create a hole in time through which data could be transmitted without any sign it had ever been sent.

Optical physicist Martin McCall of Imperial College, London came up with the theory underlying the technique, which could prevent data from being intercepted or leaving any sort of record. McCall theorized that, by challenging light rays around an object, it would be possible to create a “spacetime cloak” of invisibility. Because “channeling” the light means pulling light apart in time as well as physical space, the pocket created exists as a bubble of physical space created in a time slightly different from the space around it.

An editorial in Nature suggested manipulating spacetime in this way could hide events within the bubble because they would never have happened within the “normal” space and time around them. McCall’s own paper on temporal cloaking (PDF) also described the technique as constituting a “history editor.”

Temporal cloaking is only feasible within a fiberoptic environment–an environment in which the refractive index of light could be manipulated. The refractive index is the optical property that regulates how quickly light travels through the material. The speed of light in a vacuum is constant, but can be substantially slower for light travelling through materials other than a vacuum.

How to Build a Temporal Cloak

To hide an object or event within an optically controlled environment—the inside of a fiberoptic cable, for the most part – lasers pull light rays apart from one another physically, which also shifting them apart in time by forcing them to move at different speeds.

The shift is accomplished by manipulating the phase of a pulse of light—the height and frequency of the wave in which it travels. By changing the phase of beams of light so that they interfere with and cancel each other out, the intensity of the light as perceived from the outside drops to zero, though the light itself is not stopped, blocked or destroyed.

“By letting [beams of light] interfere with each other you are able to make them add up to one or zero. The zero is a hole where there is nothing,” according to graduate student Joseph Lukens, a co-author on the paper.

Any chunk of data going through the fiberoptic connection within a space whose light intensity is zero is cloaked because it effectively doesn’t exist in relation to the light or data in the rest of the stream of light and data.

Researchers at Cornell proved the feasibility of the theory in 2011 and again in 2012 by creating a working temporal cloak in a lab environment. The area of zero light intensity they created was so small, however, that it amounted only 1/10,000th of a percent of the time available to send data through a fiber connection.

The Purdue researchers pushed their result up to 46 percent of the available data-transfer time, bringing the technique much closer to practical application. They did it using a set of phase modulators and other gear considered to be off-the-shelf equipment in commercial optical communications. The Cornell team used, among other things, a rare and expensive femtocell laser.

However it’s accomplished, the cloak should be completely effective because, even for someone monitoring the flow of light and data through a fiber connection, the cloaked space appears not to exist.

“It looks like no signal is being sent,” Lukens said. “And you can turn it on and off, so if they suspected something strange was going on you could return it to normal communication.”


Image: Joseph Lukens, Purdue University

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