Spasers, Plasmons, and Computers-The Next Generation

[LenS]

This is an interesting look into the future of optical computing:

Source: Technology Review: The Smallest Laser Ever Made
Address :
http://www.technologyreview.com/comp...249/?nlid=2276

Surface-plasmon lasers could enable a new generation of computers based on nanophotonics.

By Katherine Bourzac
Monday, August 17, 2009

Researchers have demonstrated the smallest laser ever, consisting of a nanoparticle just 44 nanometers across. The device is dubbed a "spaser" because it generates a form of radiation called surface plasmons. The technique allows light to be confined in very small spaces, and some physicists believe that spasers could form the basis of future optical computers just as transistors are the basis of today's electronics.

While the best consumer electronics operate at speeds of about 10 gigahertz, Mikhail Noginov, professor of physics in the Center for Materials Research at Norfolk State University in Norfolk, VA, notes that optical devices can operate at hundreds of terahertz. Optical devices are, however, difficult to miniaturize because photons can't be confined to areas much smaller than half their wavelength. But devices that interact with light in the form of surface plasmons can confine it within much tighter spots.

"There's currently a big effort, mostly theoretical, towards designing a new generation of nanoelectronics based on plasmonics," says Noginov. Unlike other previous plasmonic devices, spasers are an active element that can produce and amplify these waves. Noginov co-led the development of the new spaser with Ulrich Wiesner of Cornell University and Vladimir Shalaev and Evgenii Narimanov of Purdue University. The work is described today in the journal Nature.

The spaser made by Noginov and his collaborators consists of a single nanoparticle just 44 nanometers in diameter, with different parts that perform functions analogous to those in a conventional laser. In a normal laser, photons bounce between two mirrors through a gain medium that amplifies the light. The light in a spaser bounces around on the surface of a gold sphere in the nanoparticle's core in the form of plasmons.

The challenge, says Noginov, is to make sure that this energy does not dissipate rapidly from the metal surface. His team accomplished this by coating the gold with a layer of silica embedded with dye. This layer acts as a gain medium. Light from the spaser can remain confined as plasmons or it can be made to leave the particle surface as photons in the visible-light range. Like a laser, the spaser must be "pumped" to supply the necessary energy. Noginov's group accomplishes this by bombarding the particle with pulses of light.

The size of a conventional laser is dictated by the wavelength of the light it uses, and the distance between the reflective surfaces can't be smaller than half the wavelength of the light--in the case of visible light, about 200 nanometers. The "beauty" of the spaser is that it gets around this limitation by using plasmons, says Noginov. Spasers could probably be made as small as one nanometer. Any smaller than that, Noginov explains, and the nanoparticles' functionality breaks down.

Noginov and his collaborators are not the first to make a nanolaser. This July, researchers led by Cun-Zheng Ning, professor of electrical engineering at Arizona State University, and Martin Hill of Eindhoven University in the Netherlands created a nanolaser about 100 nanometers wide, using different materials. Ning and Hill's nanolaser was the first to overcome the wavelength constraints on the size of lasers. The work published today, however, is the first example of a spaser.

"The spaser works about a thousand times faster than the fastest transistor, while having the same nanoscale size," says Mark Stockman, professor of physics at Georgia State University. "This opens up the possibility to build ultrafast amplifiers, logic elements, and microprocessors working about a thousand times faster than conventional silicon-based microprocessors."

Stockman predicted the phaser in 2003 with David Bergman, professor of physics at Tel Aviv University in Israel. The creation of the spaser, says Bergman, "is a beautiful piece of work."

Spasers are likely to find their first application not in optical computing but in places where conventional lasers are used today, says Noginov. Indeed, "a more near-term application is in the magnetic data-storage industry," says Sakhrat Khizroev, professor of electrical engineering at the University of California, Riverside, who is also developing nanolasers. The magnetic data-storage media used for today's hard disks are reaching their physical limits; one way of extending its capabilities is to heat the media with very small spots of light during recording, which could be done with nanolasers, says Khizroev. However, the researchers caution, any applications are probably years away.

[nanonyme]

Sounds pretty SciFi to me. I'll be more impressed though when there's a real-life application on it. Don't want to have the same thing as with quantum computers over and over again. (as in, neat technology, someone makes a prototype, not practically feasible, disappears back to theories)

[LenS]

Hi, this is very advanced lab research, but some breakthroughs are being made. It's still several years away from consumers. The underlying scientific principles are understood though, mostly. Given the huge advances over present systems: speeds 3 orders of magnitude faster, very low heat (no electrons to heat up chips and wires) and the ability to use present manufacturing techniques, expect the big guns, (Intel, IBM, etc.) to be developing this already.

I'm not sure what you're getting at with quantum computers. They're a long way in the future and no one really knows how to make them or even all the principles behind them. The problem may be that what the media refers to as a quantum computer is just a new explanation of a principle involving quantum entanglement. The implication as well as the principles of which are still being discovered and debated. This is still a very undeveloped science. Quantum computing is just a journalistic buzz term to get attention. We're nowhere near building a quantum computer. We don't even understand how or why quantum entanglement works. We just know it does or at least seems to. From the WIKI article below:
On the other hand, quantum mechanics has been highly successful in producing correct experimental predictions, and the strong correlations predicted by the theory of quantum entanglement have now in fact been observed.

For a more detailed look at it try:
Source: Quantum Entanglement and Information (Stanford Encyclopedia of Philosophy)
Address : <http://plato.stanford.edu/entries/qt-entangle/>

5. Quantum Computation
Quantum information can be processed, but the accessibility of this information is limited by the Holevo bound (mentioned in Section 3). David Deutsch (1985) first showed how to exploit quantum entanglement to perform a computational task that is impossible for a classical computer.

Wiki has some good info too:
Source: Quantum entanglement - Wikipedia, the free encyclopedia
Address : <http://en.wikipedia.org/wiki/Quantum_entanglement>
Applications of entanglement

Entanglement has many applications in quantum information theory. Mixed state entanglement can be viewed as a resource for quantum communication. With the aid of entanglement, otherwise impossible tasks may be achieved. Among the best known applications of entanglement are superdense coding and quantum state teleportation. Efforts to quantify this resource are often termed entanglement theory.[7] [8] Quantum entanglement also has many different applications in the emerging technologies of quantum computing and quantum cryptography, and has been used to realize quantum teleportation experimentally[9]. At the same time, it prompts some of the more philosophically oriented discussions concerning quantum theory.[citation needed] The correlations predicted by quantum mechanics, and observed in experiment, reject the principle of local realism, which is that information about the state of a system can only be mediated by interactions in its immediate surroundings and that the state of a system exists and is well-defined before any measurement. Different views of what is actually occurring in the process of quantum entanglement can be related to different interpretations of quantum mechanics. In the previously standard one, the Copenhagen interpretation, quantum mechanics is neither "real" (since measurements do not state, but instead prepare properties of the system) nor "local" (since the state vector |\psi\rangle comprises the simultaneous probability amplitudes for all positions, e.g. |\psi\rangle \to \psi(x,y,z)); the properties of entanglement are some of the many reasons why the Copenhagen Interpretation is no longer considered standard by a large proportion of the scientific community.

A 2008 quantum physics experiment performed in Geneva, Switzerland has determined that the "speed" of the quantum non-local connection (what Einstein called spooky action at a distance) has a minimum lower bound of 10,000 times the speed of light.

What that last paragraph means is that it was just last year that the minimum lower speed of data transfer over a non-local connection between entangled photons was shown to be at least 10,000 times the speed of light! That's just the minimum. It could be millions or billions or more. Clearly this involves a new understanding of the physical forces in the universe. An explanation for quantum gravity may help.

[nanonyme]

Well, actually they do know how to build quantum computers too afaik but that's besides the point.
The point was there's lots of theories and might-be's going on and I've grown sceptic enough not to believe this kind of stuff has any significance until I see it in stores.

[suokko]

Well, actually they do know how to build quantum computers too afaik but that's besides the point.
The point was there's lots of theories and might-be's going on and I've grown sceptic enough not to believe this kind of stuff has any significance until I see it in stores.

It takes years to get stores. But I think that some laboratory quantum machines are already able to do simple calculations for short time. But you will be quite old before you will be able to buy one :P

[nanonyme]

It takes years to get stores. But I think that some laboratory quantum machines are already able to do simple calculations for short time. But you will be quite old before you will be able to buy one :P

Point missed again, I think. It was that while these technologies have undeniable theoretical potential, proving that they have real potential outside SciFi and laboratory applications will probably not happen in a long time and before it happens, we have no proof it should actually be interesting anywhere else than academia.

[LenS]

Nobody has a clue on how to build a quantum computer, however that doesn't prevent anyone from throwing the term around. It's stylish and sounds impressive, actually using quantum mechanics and quantum effects, i.e. quantum entanglement, in a computer is a long way away.

There is a trend to equate the emerging optical computing technologies with quantum computing. Again that is purely a marketing ploy, designed to attrack attention and in many cases funding. Optical computers using spasers like the ones mentioned in the article will be no more "quantum computers" than the CD or DVD drives and players you have now are "quantum scanning devices". I expect if they came out now you would see quantum used extensively in their descriptions.

The article I posted doesn't mention quantum anywhere. That's because it isn't. It's "just" a technological breakthrough in miniaturizing lasers. The BIG news is shrinking the lases size down to less than half the wavelength of light. The development of spasers is now an engineering problem not unlike microchip die shrinks from 65nm to 45nm to 32, 28nm and less. This is a challenge, nonetheless, but given the payoff, and the resources able to be brought to bear on it, I expect results sooner rather than later.

If you're interested in more info on optics, quantum optics, quantum computers, and discussion on the admittedly vague line between them here's three good articles:

http://www.sciencedaily.com/releases...0709132059.htm
Miniaturized Lasers Can Emit Quantum Light

For more than 100 years it has been known that light comes in small packages, the so-called photons. The discovery of this quantization of the light field has opened up a new field of physics -- quantum optics. In the sixties one of its pioneers, the Nobel Prize winner Roy Glauber, suggested to characterize light sources according to the sequence of their emitted photons. But the realization of this idea has been very limited up to now.

(Interesting definition of quantum light emission)

http://www.sciencedaily.com/releases...0709140806.htm

Quantum Computers And Tossing A Coin In The Microcosm

When you toss a coin, you either get heads or tails. By contrast, things are not so definite at the microcosmic level. An atomic 'coin' can display a superposition of heads and tails when it has been thrown. However, this only happens if you do not look at the coin. If you do, it decides in favour of one of the two states. If you leave the decision where a quantum particle should go to a coin like this, you get unusual effects. For the first time, physicists at the University of Bonn have demonstrated these effects in an experiment with caesium.

(quantum effects change the "random walk" example around 180 degrees)

http://www.sciencedaily.com/releases...0608095042.htm

Manipulating Light On A Chip For Quantum Technologies

A team of physicists and engineers at Bristol University has demonstrated exquisite control of single particles of light — photons — on a silicon chip to make a major advance towards long-sought-after quantum technologies, including super-powerful quantum computers and ultra-precise measurements.....

....For example a quantum computer relies on the fact that quantum particles, such as photons, can exist in a “superposition” of two states at the same time — in stark contrast to the transistors in a PC which can only be in the state “0” or “1”.

(That last paragraph goes a long way in explaining the difference between a quantum computer and a regular one, as well as pointing out the advantages of quantum cryptography. Intercepting a quantum encoded message wil alter it in detectable ways, so the receiver will always be aware of the interception.)

On the other hand a laser or spaser in a computer or DVD player, etc. emits a string of 0's and 1's, just like an electronic circuit. No quantum effects. You do get extremely fast data speeds and no electrical interference or heat. They're talking about a potential speedup of one thousand times. That's a difference in playing Crysis at 20fps or 20,000fps!!!

[nanonyme]

You apparently try to adamantly miss my point.
I did not say they are related technology-wise. Only as in that both are technologies that might or might not be feasible to actually implement in real-life applications. And yes, there does exist a quantum processor. It's located in Yale University, I think. Doesn't do anything useful though afaik since it's only a two-qubit machine. The technology exists in laboratories, just like spasers nowadays do. That's my point.

[LenS]

The point I was making is that spasers actually exist and implementing the tech is just a matter of refining the production techniques and then making the masks. Quantum computers DO NOT EXIST, at least in any meaningful way. Computing with a few ions at temperatures near absolute zero is a long, long, way from a useful computer:

That kind of processor is still a way away. The current record for qubit manipulation is held by practitioners of the ion-trap technique, which uses oscillating electric fields to hold atomic ions in place, like eggs in a box, chilled to within a few degrees of absolute zero. Information is encoded in each ion's energy state. Whereas computing in a conventional processor is done by switching transistor currents on and off, the qubits are manipulated by firing a carefully designed laser pulse at the ions to put them into a particular superposition state.
Ions or dots?

In August this year, Wineland's group at NIST reported a milestone achievement. Taking two ions, they used a series of carefully calibrated laser pulses to perform some simple computations with them and read out the results. They could also move the ions around the processor without losing the information encoded on them, and repeat the process. In other words, their system does everything that a basic conventional computer should do (Science, DOI: 10.1126/science.1177077).

If you don't know wiki says: An ion is an atom or molecule where the total number of electrons is not equal to the total number of protons, giving it a net positive or negative electrical charge.

When a "milestone achievement" is using two ions, cooled to near absolute zero to reduce decoherence, performing very simple calculations, a real usable computer is far, far, away. This is a good article on quantum computers and where I got the first quote:

http://www.newscientist.com/article/...html?full=true
WHATEVER happened to quantum computers? A few years ago, it seemed, it was just a case of a tweak here, a fiddle there, and some kind of number-crunching Godzilla would be unleashed upon us. Just as digital processors changed our lives in ways hard to imagine a few decades ago, the monstrous information processing power of individual atoms and electrons would mean that computing - and the world - would never be the same again.

We're still waiting. In 2007, a Canadian company called D-Wave unveiled what it claimed was a quantum computer that could solve a sudoku puzzle, but there remains deep scepticism whether it is truly a quantum computer. Meanwhile, we seem stuck with the conventional, "classical" computers that rattle and purr away on our desks, toggling currents of electrons in billions of silicon transistors to produce the numbers, words and images that frame our lives....

...The premise behind a quantum computer is simple - provided you swallow the unpalatable quantum truths that underlie it. One is that objects such as atoms and electrons are not confined to being either this or that, as the objects of our everyday macroscopic world are; they can be both this and that at the same time. They might, for instance, be spinning clockwise and anticlockwise simultaneously, or adopt two different energy states at once. This is known as superposition.

What's more, these ambiguous quantum characters can club together so that what you do to one affects the others. This is the phenomenon of entanglement or, if you're Einstein, "spooky action at a distance". Together, the characteristics of superposition and entanglement make for a computer of awesome power.

The whole article is very informative if you're interested in quantum computing and want to get beyond the mainstream hype and scientific illiteracy.

[nanonyme]

I know physics plenty enough to know what an ion is, thank you very much.
What I don't know is why you spend the last two of your paragraphs quoting my why quantum computers are superior to old-fashioned computers. I do know. Do you even understand what you're quoting? That's trivial, everyone knows how qubits are supposed to work who has ever heard anything about quantum computers. I might not have thought of using lasers but then again, I don't design quantum computers myself. Using a coherent light source for it is likely very intuitive if you have anything to do with the practical applications.
Then again, the very fact that there's been new information produced about them this year proves that quantum computer technology is very much not dead but actively being researched and is yielding some results albeit not yet anything you can use as a supercomputer (which is imo what quantum computers would be used for if someone managed to make powerful enough a one to be useful, not as desktop computers like that writer - hopefully jokingly - referred to)
Two years ago is just so ancient history.