Scientist make a leap in quantum computing

Feb 05, 2010 by Kitta MacPherson
Spin qubits, which could be the core logic elements of quantum computers, are cooled in a device called a dilution refrigerator to temperatures near absolute zero in order to exploit the mysterious rules of quantum mechanics. Photo: Princeton University/Brian Wilson

( -- A major hurdle in the ambitious quest to design and construct a radically new kind of quantum computer has been finding a way to manipulate the single electrons that very likely will constitute the new machines' processing components or "qubits."

Princeton University's Jason Petta has discovered how to do just that -- demonstrating a method that alters the properties of a lone electron without disturbing the trillions of in its immediate surroundings. The feat is essential to the development of future varieties of superfast computers with near-limitless capacities for data.

Petta, an assistant professor of physics, has fashioned a new method of trapping one or two electrons in microscopic corrals created by applying voltages to minuscule electrodes. Writing in the Feb. 5 edition of Science, he describes how electrons trapped in these corrals form "spin qubits," quantum versions of classic computer information units known as bits. Other authors on the paper include Art Gossard and Hong Lu at the University of California-Santa Barbara.

Previous experiments used a technique in which electrons in a sample were exposed to . However, because it affected all the electrons uniformly, the technique could not be used to manipulate single electrons in spin qubits. It also was slow. Petta's method not only achieves control of single electrons, but it does so extremely rapidly -- in one-billionth of a second.

"If you can take a small enough object like a single electron and isolate it well enough from external , then it will behave quantum mechanically for a long period of time," said Petta. "All we want is for the electron to just sit there and do what we tell it to do. But the outside world is sort of poking at it, and that process of the outside world poking at it causes it to lose its quantum mechanical nature."

When the electrons in Petta's experiment are in what he calls their quantum state, they are "coherent," following rules that are radically different from the world seen by the naked eye. Living for fractions of a second in the realm of quantum physics before they are rattled by external forces, the electrons obey a unique set of physical laws that govern the behavior of ultra-small objects.

Scientists like Petta are working in a field known as quantum control where they are learning how to manipulate materials under the influence of quantum mechanics so they can exploit those properties to power advanced technologies like . Quantum computers will be designed to take advantage of these characteristics to enrich their capacities in many ways.

In addition to electrical charge, electrons possess rotational properties. In the quantum world, objects can turn in ways that are at odds with common experience. The Austrian theoretical physicist Wolfgang Pauli, who won the Nobel Prize in Physics in 1945, proposed that an electron in a quantum state can assume one of two states -- "spin-up" or "spin-down." It can be imagined as behaving like a tiny bar magnet with spin-up corresponding to the north pole pointing up and spin-down corresponding to the north pole pointing down.

An electron in a can simultaneously be partially in the spin-up state and partially in the spin-down state or anywhere in between, a quantum mechanical property called "superposition of states." A qubit based on the spin of an electron could have nearly limitless potential because it can be neither strictly on nor strictly off.

New designs could take advantage of a rich set of possibilities offered by harnessing this property to enhance computing power. In the past decade, theorists and mathematicians have designed algorithms that exploit this mysterious superposition to perform intricate calculations at speeds unmatched by supercomputers today.

Petta's work is using electron spin to advantage.

"In the quest to build a quantum computer with electron spin qubits, nuclear spins are typically a nuisance," said Guido Burkard, a theoretical physicist at the University of Konstanz in Germany. "Petta and coworkers demonstrate a new method that utilizes the nuclear spins for performing fast quantum operations. For solid-state quantum computing, their result is a big step forward."

Petta's spin qubits, which he envisions as the core of future quantum logic elements, are cooled to temperatures near absolute zero and trapped in two tiny corrals known as quantum wells on the surface of a high-purity, gallium arsenide chip. The depth of each well is controlled by varying the voltage on tiny electrodes or gates. Like a juggler tossing two balls between his hands, Petta can move the electrons from one well to the other by selectively toggling the gate voltages.

Prior to this experiment, it was not clear how experimenters could manipulate the spin of one electron without disturbing the spin of another in a closely packed space, according to Phuan Ong, the Eugene Higgins Professor of Physics at Princeton and director of the Princeton Center for Complex Materials.

Other experts agree.

"They have managed to create a very exotic transient condition, in which the spin state of a pair of electrons is in that moment entangled with an almost macroscopic degree of freedom," said David DiVencenzo, a research staff member at the IBM Thomas J. Watson Research Center in Yorktown Heights, N.Y.

Petta's research also is part of the fledgling field of "spintronics" in which scientists are studying how to use an electron's spin to create new types of electronic devices. Most electrical devices today operate on the basis of another key property of the electron -- its charge.

There are many more challenges to face, Petta said.

"Our approach is really to look at the building blocks of the system, to think deeply about what the limitations are and what we can do to overcome them," Petta said. "But we are still at the level of just manipulating one or two quantum bits, and you really need hundreds to do something useful."

As excited as he is about present progress, long-term applications are still years away. "It's a one-day-at-a-time approach," Petta said.

Explore further: Serious security: Device-Independent Quantum Key Distribution guards against the most general attacks

Provided by Princeton University

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3.9 / 5 (8) Feb 05, 2010
So...quantum computers are both possible and impossible, and everything between too...

The glass is full, half full, half empty, and empty all at the same time!
2 / 5 (9) Feb 05, 2010
This work is not only awesomely inspired and pioneering, it validates the most commonly held Eastern spiritual belief & awareness; namely that at the quantum level, reality plays myriad wondrous games with us (we are everywhere at once); we are the universe and the universe is enfolded within us (see Fractal Universe), there is a realm beyond our physical world that echoes ripples of a higher cosmic / universal consciousness. We are defining the pure meditative state, an alertness to how our intelligent and sentient God within experiences itself subjectively. Buddha enlightenment has now been scientifically validated.

The one fallacy that Western cultural & scientific dogma betrays of itself is its dogged assumption that all the constituent parts that comprise our reality are absolute: God either is or isn't, true or false, can or can't. However, it seems inevitable now that we cannot escape the undeniable fact: all states are possible simultaneously, & consciousness is the sheeit.
4.3 / 5 (7) Feb 05, 2010
@skand1nsky: Are you trying to bait us or something? Eastern spiritual belief is based on vague concepts. Quantum Physics is based on specific and focused models and logic. It drives me crazy when people try to use science to back up beliefs in faith. Science and faith have nothing to do with each other and one cannot prove or disprove the other.
1.2 / 5 (5) Feb 05, 2010
Of course this work is science and not religion. It only proves what it proves.

Nevertheless, there is actually a strong similarity between quantum mechanics and Eastern philosophy/religion. So strong, that it is worth investigating.
1.2 / 5 (5) Feb 05, 2010
fuzz54: I would think it's more the difference between objective and subjective sciences (the latter of which, as I understand, was proposed by Rene Descartes as a viable methodology necessary when the former is not meeting desired goals).

Remember that we are still taking for granted much of how today's technologies, including even light bulbs, really work, and as such we place faith in the continued operation of such voodoo.

This conversation brings to the mind of this particular responder the bouncing of theorist brains between the realities of quanta and consciousness.
2.2 / 5 (6) Feb 06, 2010
Did they even bother to read the title?

Scientist make a leap in quantum computing.

1.6 / 5 (8) Feb 06, 2010
No baiting, fuzzli, I'm merely bringing 'coherence' to the science-spirituality relationship. Let me ask you something: if you acknowledge that science is an empirical movement, reliant only on observations and sensory measurement (usually sight), then how do you know you have feelings and thoughts? Have you ever seen them? Have you ever heard them ringing inside your bones or throbbing in your cranium? No, they are experiential, much like the divine. A taste of the Universal Truth is absolute -- there's no going back from there. Try a psychedelic like DMT or mescaline some time, or perhaps sample a wee bit of meditation. The point is, man has always had the capacity to transcend the narrow confines of our physical reality, within which science revels. However, cast aside our restricted worldview, and we're suddenly thrust into the world of the intangible, the formless, the ground of being. Quantum mechanical superposition is merely our way of saying 'higher dimensions of existence'.
1.6 / 5 (7) Feb 06, 2010
For further reading, look up 'Biocentrism' on Wiki, as well as buy a second-hand edition of Timothy Leary's 'The Psychedelic Experience'
2.1 / 5 (9) Feb 06, 2010
Oh, and as an aside, I've a Masters in Particle Physics. Believe me, the most annoying aspect of scientific reductivism is its penchant for fundamentalism, one perhaps as heinous and defeatist as religious extremism.
5 / 5 (5) Feb 06, 2010
One paragraph to deal with the actual discovery, the rest of the article to deal with background information. I appreciate the refresher course in layman's QM, but I really could've used some more information on what these people are actually doing. I'm just slower than most, I guess.

From what I could glean, they've confirmed a pin-point method of modifying an electron's spin by using quantum wells. Still needs super-cooling, complicated fabrication and is far from doing actual computation. Yet somehow the phrasing of the article makes it seem as if these guys alone thought up the marvellous concept of quantum computing and will have a prototype ready in a few years.

I really think it's safe to assume that the majority of Physorg readers have the knowledge required to understand basic technicalities and would appreciate them more than pop-science buzz wording. The vagueness of the latter tends to stir up long-winded, pointless, off-topic, "philosophical" discussions, as one can see.
5 / 5 (5) Feb 06, 2010
honestly, listening to these off-subject debates is like sitting in a coffeeshop populated by undergrads taking their first world religions/philosophy 101 course.
@skand1nsky: When you feel something you aren't actually feeling it, you're feeling the signals from the pressure receptors in your skin. We know we are conscious because consciousness is all we are conscious of. Everything else we have to deduce through empirical reasoning because we are separated from the physical world by nature of our design. What you are doing is merely putting that separation on some ridiculous pedestal because god knows why. Get off your "high" horse and take your condescending religiobabble to erowid.
Feb 06, 2010
This comment has been removed by a moderator.
1.9 / 5 (9) Feb 07, 2010
I must admit, I find it appalling that a lot of hardcore scientific pushers fail to acknowledge that it's time to break boundaries. Separation is illusion, my friends, you have all been submerged in dualities for far too long.

We all come from the same Omega point source, that immense, impossible nothingness from which the material universe sprang forth. All matter was once connected. That awakening is an intimation of the wonder of universal oneness, of transcending our dualistic definitions to achieve a state of unity. Separation is your ego's way of keeping it's identity, and it will cling desperately to all notions of being 'apart'. This isn't religiobabble either, it's what saints and mystics have been postulating ever since the earliest tribes sampled natural hallucinogens, to have their first realisations of a higher intelligence and expanded consciousness. This isn't a high horse upon which I place myself, I'm only trying to unseat your fervent science-based zealotry.
4.2 / 5 (6) Feb 07, 2010
skand1nsky, trust me, I know what you're talking about. The problem with your approach is that you're trying to explain religion(in the broadest sense) with science and vice versa.

If you had really thought carefully about the two subjects, you would've realised that by attempting that, you're failing at both. By their definition they're two fundamentally different ways of looking at things, one rational-analytic, the other intuitive-synthetic.

Religion, as you understand it, demands the cessation of rational, dividing thought, while science is based exclusively on differentiation and categorisation. By looking for scientific proofs of religion, you're negating its very essence, while unfalsifiable religious tenets cannot form the basis of a scientific theory.

So, to sum it up in a zen fashion, you can talk science and you can feel religion, but it doesn't work the other way around.
2.6 / 5 (5) Feb 07, 2010
kasen, it comes as some consolation to my existential angst (or lack thereof) that there are others who have pondered the subject, and tried to find connective pathways between such differentiated fields.

However, I firmly believe that science, if it looks inwardly as well as at the whole holistic picture of reality, can validate the deepest, most profound mystical / metaphysical / philosophical / spiritual truths. Ultimately, differentiation is only a construct, a vestige of the human mind, programmed to compartmentalise and pigeonhole. Really, there is no distinction between these apparently distinctive explanations for our reality. Science and religion (as you describe) aren't mutually exclusive. Bill Hicks, the famous stand up comic, said it best: "Matter is merely energy condensed to a slow vibration, & we are all one consciousness experiencing itself subjectively. There's no such thing as death, life is only a dream and we are the imagination of ourselves."
3 / 5 (3) Feb 07, 2010
"Trapped in the past, Dr. Beckett finds himself leaping from life to life, putting things right that once went wrong, and hoping each time that his next leap will be the leap home."

Oh crap, read the title wrong.
Feb 07, 2010
This comment has been removed by a moderator.
4.5 / 5 (4) Feb 07, 2010
"Matter is merely energy condensed to a slow vibration

He's wrong there - If one applies particle wave duality to matter (protons, electrons, etc) - compared to electromagnetic waves matter has extremely short wavelengths and thus very high frequency.


(science) if it looks inwardly as well as at the whole holistic picture of reality

It does. But to understand the gestalt you need to analyze and understand the underlying parts. Once you do that you can step back and see the whole.

Try a psychedelic like DMT or mescaline some time, or perhaps sample a wee bit of meditation.

I think I grok your posts now (or at least where they are coming from).

Word of advice:

Meditation works a whole lot better for understanding than using psycho-active drugs ("natural" or otherwise) - the latter disrupts the natural flow of information in your brain. Said substances tend to make one more close-minded than open-minded.
2.3 / 5 (3) Feb 08, 2010
At the beginning, all that existed was infinite potential. And the Universe, seeing this, said: "Let there be me."
2.3 / 5 (3) Feb 09, 2010
However, I firmly believe that science, if it looks inwardly as well as at the whole holistic picture of reality, can validate the deepest, most profound mystical / metaphysical / philosophical / spiritual truths.
If you can explain how science can look inwardly in a useful and precise methodology then I'd love to hear it. If you can use the scientific process to unlock the secrets of the metaphysical then there is an open challenge out there that will make you richer by a million dollars. Just promise to buy me a drink when you win. http://www.randi....nge.html
1 / 5 (2) Feb 13, 2010
fuzz, i would like to thank you for your info -- i've been chasing the dream for a while now. i've seen some fantastical and magical real life events that have left me stumped for rational scientific explanations, including UFOs, heavy rock levitations, 'miracle' healings and manifestations of group consciousness. if i could only make a million off it, my life might just be radically changed.

but then again, it's never about the money. when one immerses oneself into the spiritual realm, you realise the fallacy of the reality around us -- war, politics, financial institutions, power, greed and fake life incentives. money happens to be the foremost example of the latter, the archetypal anomaly that creates only the most abhorrent feelings within a human. i could never strive for the prize, for the simple reason that it betrays my sense of doing what's right.

so, the other alternative would be to change people's lives in a more subtle way, by firstly introducing them to themselves.
1 / 5 (2) Feb 19, 2010
Good article, GREAT post-discussion. I'm a skeptical agnostic with a penchant for pattern recognition and an obsession for discovering the underlying principles between seemingly mutually exclusive phenomena. So it comes as no surprise that I yearn for the discovery of an all-encompassing knowledge of our existence. Sadly, the only thing I can say with any kind of certainty is that we are most likely no where close to any such understanding. Dialog such as this is entertaining and thought-provoking but it is also a reminder that even humanities best minds (yes that is a complement to the participants of this discussion) still have no real clue when it comes to the Tao of our existence. All-in-all I still think it to be a worthwhile exercise, not-to-mention a very enjoyable read.