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Friday, May 14, 2004
 Super-photons could make better CD players
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Message Text: Objects called super-photons could help squeeze more data from compact discs, and lead the way to more powerful computers and ultra-secure telephone and Internet lines, scientists reported.

The novel technique behind such advances is based on a bizarre trick of nature that occurs within the murky realm of quantum physics.

Morgan Mitchell, a quantum optics researcher at the University of Toronto, and colleagues have been working on performing just such entanglements with photons, the packets of energy that compose light. In addition to its two-places-at-once ability, entanglement also causes multiple photons to behave as if they were one. For example, entangling three photons means they behave as a single photon, but with three times its normal energy.

Despite the esoteric-sounding terms, entangling photons can produce some highly practical and valuable results. For example, it could help pack data more tightly onto compact disks. The data are stored on the disks' aluminum-coated reflective layer. That layer encodes data in thousands of microscopic pits, each about a half-micron wide, or 20 times narrower than a single blood cell.

The pits on a disk reflect light differently than "lands" -- the smooth parts of its surface. Each pit or land represents a bit of information. CD players read data from the disks by running over them like phonograph needles did over vinyl records, but without physical contact.

Normally, the size of the tiniest feature that can be seen is no better than the wavelength used to see it. This physical barrier is called the "diffraction limit," Mitchell explained.

The wavelength of light typically used in CD players is about 780 nanometers, or 780 billionths of a meter. This is very small -- less than one-hundredth the diameter of the average human hair. Currently, a compact disk can harbor enough pits to encode up to roughly 783 million bytes of data, or about 74 minutes of music.

By entangling photons, however, Mitchell and colleagues said they can beat the diffraction limit.

"Because the three photons behave like one super-photon," he explained, "the super-photon gives us a resolution that is three times better than an individual photon would."

Although the researchers used 810 nanometer wavelength photons, which function as infrared light -- outside the visible range -- the super-photons allowed them to resolve details on the scale of 270 nanometers.

Creating single photons is an incredibly delicate procedure. A single photon produces 10 billion-billion times less light than a 100-watt lightbulb.

"You could definitely say there may be applications to optical technologies like CD or DVD players, as long as it's added that we're not there yet," Mitchell said. "We've provided one piece of the puzzle, but there are several very important pieces still missing."
 
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