Last year researchers at Imperial College London proposed that along with being used to cloak physical objects metamaterials could also be used to cloak a singular event in time. A year later, researchers from Cornell University have demonstrated a working "temporal cloak" that is able to conceal a burst of light as if it had never occurred.
In a research paper published in the Journal of Optics last year, Prof. Martin McCall and his team at Imperial College London said it should be theoretically possible to create a "Spacetime Cloak" by using metamaterials - a class of artificial materials engineered to have properties not be found in nature - to speed up the leading edge of light waves, while slowing down the trailing half. This would create a "corridor" between the two halves, at which point their source wouldn't be observable.
To demonstrate the theory, a Cornell research team led by Moti Fridman sent a beam of light down an optical fiber and passed it through a split-time lens - a silicon device originally designed to speed up data transfer. As the beam passes through the first lens it is compressed, leaving a dead zone or gap in the flow of light. A similar lens further along the path reverses the velocity adjustments, decompressing the light wave so it appears that the light coming through the second lens is uninterrupted as if no distortion had occurred.
To test the temporal cloak's performance the researchers created pulses of light directly between the two lenses that repeated like clockwork at a rate of 41 kHz. When the cloak was off, the researchers were able to detect a steady beat, but after switching on the cloak, which was synchronized with the light pulses, it appeared as if the pulses were erased from the data stream.
Rather than relying on the properties of metamaterials as was initially proposed by McCall, the temporal cloak demonstrated by the Cornell research team relies on the fundamental properties of light and how it behaves under highly constrained space and time conditions.
The length of the cloaked area is a mere six millimeters (0.2 in) long and the effect can only lasts for 110 nanoseconds. The team says the best it can achieve will be 120 microseconds because longer durations would create turbulence in the system that would hint that an event had occurred. To achieve any measurable macroscopic effects would require an experiment on planetary or even interplanetary scales, the researchers say.
The Cornell team will present their findings in a presentation "Demonstration of Temporal Cloaking" at the Optical Society's Annual Meeting, Frontiers in Optics (FiO) 2011, being held in San Jose, California, next week.
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