Cornell University researchers have demonstrated that it’s possible to cloak a singular event in time, creating a “history editor.”

Moti Fridman and his colleagues sent a beam of light traveling down an optical fiber and through a pair of  “time lenses.” Between these two lenses, the researchers were able to briefly create a small bubble, or gap, in the flow of light. During that moment, lasting only 20 picoseconds (trillionths of a second), the gap functioned like a temporal hole, concealing the fact that a brief burst of light ever occurred.

Erasing history

Their ingenious system relies on the ability to use short intense pulses of light to alter the speed of light as it travels through optical materials, in this case an optical fiber. As the beam passes through a split-time lens (a silicon device originally designed to speed up data transfer), it accelerates near the center and slows down along the edges, causing it to balloon out toward the edges, leaving a dead zone around which the light waves curve.

A similar lens a little farther along the path produces the exact but opposite velocity adjustments, resetting the speeds and reproducing the original shape and appearance of the light rays.

To test the performance of their temporal cloak, the researchers created 41 kilohertz pulses of light directly between the two lenses. When the cloak was off, the researchers were able to detect a steady beat. By switching on the temporal cloak, which was synchronized with the light pulses, all signs that these events ever took place were erased from the data stream.

Unlike spatial optical cloaking, which typically requires the use of metamaterials (specially created materials engineered to have specific optical properties), the temporal cloak designed by the researchers relies more on the fundamental properties of light and how it behaves under highly constrained space and time conditions.

The length (6 millimeters) of the cloaked area and the length of time (20 picoseconds) it is able to function are tightly constrained by the velocity of light. Cloaking for a longer duration would create turbulence in the system, essentially pulling back the curtain and hinting that an event had occurred. And to achieve any measurable macroscopic effects, an experiment of planetary and even interplanetary scales would be necessary.

Frontiers in Optics (FiO) 2011 presentation FMI3, “Demonstration of Temporal Cloaking” by Moti Fridman et al. is at 4:45 p.m. on Oct. 17 in San Jose, California.

Ref.: Moti Fridman et al., Demonstration of temporal cloaking, arXiv:1107.2062v1