Memory storage for light-based computers

Japanese scientists working for NTT have used photonic crystals to trap light by over one nanosecond. In fact, light was trapped inside a wavelength-sized micro-cavity, delaying its transmission. So the apparent speed of light was reduced by a factor of 50,000, or just 5.8 kilometers per second. This is not the first time that physicists have 'reduced' the speed of light, but this achievement could lead to new ways of storing information in future light-based or quantum computers.

In a brief article, Japanese scientists cage light, The Register reports that scientists working for NTT have used photonic crystals to trap light by over one nanosecond. In fact, light was trapped inside a wavelength-sized micro-cavity, delaying its transmission. So the apparent speed of light was reduced by a factor of 50,000, or just 5.8 kilometers per second. This is not the first time that physicists have 'reduced' the speed of light, but this achievement could lead to new ways of storing information in future light-based or quantum computers.

Let's start with the first sentence from the article: "Scientists have used silicon crystals to trap light and slow it down to the lowest speed ever recorded in the material." Sorry, but this is not true. In October 2005, I've written a post about Californian researchers who slowed light down to 245 meters per second!

But the goal was different. The researchers at Berkeley were working on future faster communication networks by eliminating the need for optical-electronic-optical (OEO) conversions. On the contrary, the NTT Basic Research Laboratories are working on how to trap light to store data for future photonic computers.

Below is a figure describing the fabricated Si photonic crystal used by the NTT researchers. "Our device is based on a photonic crystal that comprises an array of air holes, 100 nanometers in radius, arranged in a hexagonal lattice, fabricated on a silicon chip by state-of-the-art nano-processing technology. The ultra-small optical cavity consists of a single line of missing air holes defined in the matrix of a photonic crystal acting as a photonic insulator. The key design feature is that some of the holes adjacent to the line defect are intentionally displaced outward by three to nine nanometers. This small displacement modulates the width of the line defect, thereby enhancing its ability to confine light." (Credit for figure and caption: NTT Basic Research Laboratories).

NTT fabricated Si photonic crystal

You can see more explanations and figures in what NTT calls a press release, "Success in trapping and delaying light for over one nanosecond using photonic crystals" (December 21, 2006). If all company press releases were like that, it would be refreshing: it's almost a scientific paper!

For more information, this research work has been published by Nature Photonics under the title "Trapping and delaying photons for one nanosecond in an ultrasmall high-Q photonic-crystal nanocavity" (Volume 1, Issue 1, January 2007). Here are the links to the abstract, the full text and to a PDF version (4 pages, 585 KB).

Sources: Chris Williams, The Register, December 21, 2006; and various websites

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