Quantum computing getting closer...

[Rat]

(Adapted from an article by Mark Buchanan of NewScientist magazine.)

It has recently become possible to use quantum tricks to slow down light, or even to stop it altogether. By switching the light source off at the right moment it might be possible to use "slow light" as a new way to store information for use in quantum communications and computing.

In space, light travels at 300,000 kilometres per second. It is a shade slower in glass and other materials and, physicists have found, can be made extremely sluggish in dilute gases of atoms or in an exotic state called a Bose-Einstein condensate.

In the case of a gas, the trick is first to use "control" lasers to put the atoms in a delicate quantum state that prevents them from interacting with light. This creates what physicists refer to as "electromagnetically induced transparency"- a condition in which compact pulses of light known as solitons can travel through the gas without exchanging any energy with it. The speed of the solitons is dependent on the intensity of the control lasers, and by reducing this researchers can slow the soliton or even stop it completely.

Alan Bishop and his team at the Los Alamos National Laboratory in New Mexico has shown that the stopping of such solitons may offer a convenient way to store information. They studied the equations that describe an optical soliton passing through a gas whose quantum properties are controlled by a laser beam, and explored what would happen if the control laser were suddenly turned off once the soliton had entered the gas. They showed that turning off the laser triggers a shock wave at the point where the soliton first entered the gas, which chases after the soliton and eventually catches up, stopping it in its tracks (http://www.arxiv.org/quant-ph/0411148).

While the soliton vanishes when it stops, its former presence is registered in the properties of atoms in the immediate vicinity, marking them out from the atoms elsewhere in the gas. So by turning the laser off at a precise moment, it is theoretically possible to write information onto atoms at specific locations.

"The information would last for about a thousandth of a second," says physicist Andrei Rybin of the University of Jyväskylä in Finland, a member of the team. This is a long time for light, and could provide a way for quantum computers to store information during calculations.

[Grinch]

Nerds truly are amazing people.

[quicksilver]

I wonder what happened to the humble photon
I Cant see this being of any practicle use what so ever, but it builds up our knowledge of physics, and the manipulation of minute particles of matter.
That may be important in some other sphere of science.
Not so long live the solitons !

[nesman]

It's all good untill you divide by zero and turn your computer into a time machine.

[Rat]

I Cant see this being of any practicle use what so ever

You can't? Does your processor work so slowly that it can't handle one thousand operations per second? Most computers still in operating condition are capable of performing many more switches than that. (We tend to work in terms of Gigahertz now remember?) If short term memory can be controlled by switching at light speed, Moore's law is going to hold good for some years yet to come. Bye bye transistors! Helloooo solitons.

BTW photons are still a hot topic. Photon entanglement is clever stuff.

[quicksilver]

Unfortunately , as soon as the processor has done its stuff it goes back to bog standard electronics, so all that increase in speed is lost, still I,m sure someone will make something useful with it.

[Rat]

You've totally missed the point quicks. At present, the bog standard electronics is the rate limiting step. Physicists have already produced atomic sized lasers. Now they can stop light to 'program' gas molecules. Nobody says that Intel or AMD will start making quantum processors overnight but the fact that switches and memory can now both be constructed at the molecular level means things will move on. Think of the bigger picture. It's less than 6 months since nanofibres of semi-conductors were first grown (again using lasers for point-heating) and they haven't been implemented in processor construction yet - but they will be because they're much smaller than existing micro-transistor circuitry. Quantum mechanics for processor technology is further down the line even than this, but it *is* coming.

[quicksilver]

I dont believe the processor speeds we are using now,are the limiting factor in computing and as long as you need to convert light into elcectrical inpulses there will be a speed loss.

[Rat]

Granted and agreed. Speed loss is necessary in any kind of conversion. Transmission times around the circuitry however will be greater than is presently possible.
I don't expect any of this stuff to be applied anytime soon. On the other hand, I fully expect to see computers of similar power to those that currently sit on desktops everywhere to be hiding in boxes smaller than wristwatches during my lifetime. I guess I have about 50 years left.

[Rat]

An update!!!

Light from silicon-based lasers has always been too erratic to be of any practical use. But two experiments reported last week raise hopes that the lasers will eventually be steady enough to drive ultra-fast optical microchips. Both experiments use light from an external laser to "pump" the silicon atoms into a state in which they can emit light.

Engineers at Intel in California got a silicon laser to produce a steady beam by guiding the pumping laser through an S-shaped path in a silicon wafer (Nature, vol 433, p 725). The longer path means the pumping light can be amplified enough to sustain a continuous output from the silicon.

Another challenge was to control silicon laser beams electrically. Engineers at the University of California in Los Angeles succeeded in switching a silicon laser on and off by varying a voltage applied across the path of the pumping beam (Optics Express, vol 13, p 796).

[Red XIII]

what's next? fusion power supplies?

Interesting concept they have going, I just don't see its application till Im well into my 50s

[Rat]

I just don't see its application till Im well into my 50s

Take note everyone! Let's wait and see how old Red is when these things get into end-users' machines.

[Red XIII]

who say you'll remember!!!

*goes into covert mode!*

[Rat]

Now it's plasmons!

Computer chips capable of speeding data around by rippling the electrons on the surface of metal wires just got a step closer, researchers say.

Mark Brongersma, at Stanford University in Palo Alto, California, US has found a new way to model the three-dimensional propagation of these ripples - called plasmons - in two dimensions. He says the new model is much simpler and more intuitive than existing simulations and will be crucial in the design of plasmonic components for computer chips.

Plasmons travel at the speed of light and are created when light hits a metal at a particular angle, causing waves to propagate through electrons near the surface.

"Right now, the simulations are so complex that only a few groups in the world can carry them out," says Brongersma. "The new model came out of a desire for much simpler models."

Currently the biggest application for plasmons is in gold-coated glass biosensors, which detect when particular proteins or DNA are present - the bio-matter changes the angle at which light hitting the surface produces the most intense plasmons.

But scientists would love to use plasmons to ferry data around computer chips because they could operate at frequencies 100,000 times faster than today's Pentium chips, without requiring thicker wiring.
Light speed

Ordinary light waves can transmit data at similarly high frequencies, but using photons to carry data across a computer chip is currently impossible. This is because the size of the optical fibre that carries the light waves must be about half the wavelength of the light, which is over twice the thickness of the wires in modern chips.

"The big advantage of plasmons is that you can make the devices the same size as electrical components but give them the speed of photons," says Brongersma. Plasmon-carrying wires could also be made out of copper or aluminium, like the interconnects on today's computer chips.

Brongersma points out that the speed of these interconnects has become a key limiting factor. While transistors have become faster at switching as manufacturers find ways to make them smaller and smaller, the wires that carry the data are not getting any faster. "We need to find new ways to connect transistors together," he says.
Design issues

To develop the new, simpler model, Brongersma showed that the intensity pattern of a plasmon travelling across the surface of a metal strip was the same as for a light wave travelling through an optical fibre. He says this indicates that traditional "ray-tracer" programs for modelling light waves should work for plasmons too.

Such models are necessary if devices that generate and route multiple plasmons are ever to be designed, Brongersma says. He will publish the work in an upcoming issue of Optics Letters.

"Any advance that aids design is a good thing," says Harry Atwater of the California Institute of Technology in Pasadena, US. But he warns that a bigger hurdle to plasmon-based computer chips is finding plasmon sources that are compatible with silicon. "The most important element is not the design tools, it is having the ingenuity to know what to do with them," he says.

[quicksilver]

Nice to see the scientists have caught up with my little objection two months ago.

Brongersma points out that the speed of these interconnects has become a key limiting factor. While transistors have become faster at switching as manufacturers find ways to make them smaller and smaller, the wires that carry the data are not getting any faster

I envision the powerhouses of tomorrow to be a mixture of biomatter and optical electronics, but I,m pretty confident still that no all optical arrangement is going to take the crown for speed, we mustnt confuse the fact that light can travel at very fast speeds with the idea that it will do anything useful in that time.