Quantum Computing Using Traditional Transistors

Ocean Consulting writes "UCLA is reporting progress on the quantum computing front by announcing success in controlling the spin of a single electron using an ordinary transistor." It's been a long road for the researchers involved, and even the project lead, Hong Wen Jiang admits, "...our initial theoretical calculations were very favorable, and gave us confidence to persevere."

Comments

Awesome!

[erick99]

Once they get the cost down for actually reading the the state of an electron this will be awesome. Imagine only needing 100 transistors to:

"With 100 transistors, each containing one of these electrons, you could have the implicit information storage that corresponds to all of the hard disks made in the world this year, multiplied by the number of years the universe has been around," Yablonovitch said. "And why stop with 100 transistors?"

That is pretty amazing.

Cheers!

Erick

Re:Awesome!

[Sgs-Cruz]

It has to do with all the possible quantum states of the system. I.e. if each transistor has two states, there's 2^100 quantum states of the system when the system contains 100 transistors.

Actually making use of those squillions of quantum states is something else entirely. It's not like you can just store that much information in 100 transistors, it's that it contains all possible combinations of those 2^100 quantum states while it's running.

Quantum terms

[Decaff]

I wish physicists would be more cautious in their use of language.

In the article it states: "The UCLA team succeeded in flipping a single electron spin upside down."

Considering that the term 'spin' is just a metaphor for a quantum-mechanical property that has no equivalent in our everyday experience, it makes no sense to talk about 'flipping' it, or the spin being 'upside down'.

Neat achievement though....

Re:Quantum terms

[Ruie]

Actually this was pretty precise.

You see electron spin space is a two dimensional complex space. It is tied to usual 3 dimensional real space via representation of SU(2) - so it is hard to say which direction corresponds to which.

However, if one fixes a basis in usual space one can use it to fix a particular representation of SU(2).

Furthermore, one of the basis vectors will have a particularly simple Pauli matrix corresponding to it - the direction of this vector is usually called "quantization axis".

Often this vector corresponds to "z" axis. The "up" spin is then defined as (1,0) and the "down" spin is (0,1). So flipping the spin upside down is just switching components.

Another justification for talking about "up" and "down" is that spin vectors are usually written as columns so there is an upper entry and the lower entry.

Re:Quantum terms

[Ruie]

I guess we have different points of view them..

Just for fun let me continue.. :)

What do you mean by nothing is spinning ? What does it mean to be spinning ?

I can tell when a ball spins because I can see it. But does Earth spin ? I can't see the rotation but I can infer it with tools.

Do small pieces of matter (like dust) spin ? Maybe.

Now it turns out when you look at very small pieces of matter (like particles) then the laws of nature we are accustomed to change. This is simply because we do not teach quantum mechanics in kindergarten.

One that is aware of quantum mechanics see its manifestations on macro scale - they are just commonly perceived as separate phenomena (like electricity).

Now classical rotation corresponds precisely to quantum spin.

When you consider two quantum particles (with spins J1 and J2) as a single system the result is a tensor product of spins - so you get a direct sum of representations between |J1-J2| and |J1+J2|.

When you have a lot of particles comprising a ball you can still describe it on a quantum mechanical level - it would be a direct sum of representations of SU(2) with numbers between 0 or 1/2 and N/2 (where N is the number of particles).

The "usual" behaviour you are accustomed to happens because the particles have weakly interacting spins and are unordered.

The quantum part can manifest in macroscopic situations, albeit in (so far) very restricted circumstance - for example quantum Hall effect.

My point is that you can start at very small with quantum notion of spin and then as you increase the number of particles in your system you will gradually reach the situation where classical notions of spin are a *very* good approximation.

Re:Quantum terms

[Ruie]

The "usual" behaviour you are accustomed to happens because the particles have weakly interacting spins and are unordered.

Sorry, this is not right. Usual behaviour is due more to particles changing positions than to remnants of quantum behaviour.

So your point would hold if we restrict ourselves to considering only spinning that is due to bodies rotating one around another.

My point would hold if we allow idealization of solid body - i.e. an object with an intrinsic spin.

For example, you could consider a ball as multitude of molecules changing positions around each other.

Or we can consider it as idealized object (sphere) with an axis of rotation - I usually think of it this way. (So throwing a ball is composed of two parts - imparting linear movement and spinning the ball around with fingers. Note that usage of "spinning" as independent of movement.)

Quantum spin is the right generalization of intrinsic spin at the quantum level.

Ready for Doom 4!

[Evil Butters]

Cool... With one of these new quantum computers, I should be able to meet the minimum requirements for Doom 4! Now if only I could get my quantum video card to work...

Re:Secure communications?

[cephyn]

Here's what i never understood, maybe you or someone can help me out...

if eavesdropping on the encrypted transmission destroys it, couldnt the eavesdropper do so on purpose everytime, effectively jamming all transmission? Little point in having a secure way to communicate if no message can ever get through.

Don't hold your breath...

[Dr. Mu]

I Google-whacked 'quantum-computing Clear-Channel' and already got 63 hits.

boo. Article gets a thumbs down. No, the finger.

[sacrilicious]

Quantum computing, which holds the promise of nearly unlimited processing power, secure communications and the ability to decode encrypted conversations by terrorists and others

I was willing to forgive a little hype until the idiocy about terrorists. Decided maybe I was just cranky, then read:

While flipping a single electron was difficult, detecting that they had actually done so proved even harder. "We couldn't tell whether it was flipping," Jiang said. "It was like looking for a needle in a haystack."

Wow, I'm so illuminated by this "needle in a haystack" imagery. Before it I had no idea what was going on, but now it all seems so clear.

This article blows. Can we get something better on slashdot please? Something that doesn't make me feel I'm being lumped in with people who need things drastically dumbed down, and/or rationalized in the name of "fighting terrorists"?

Implicit Disinformation

[reversible physicist]

Quantum communication is already practical, and provides a secure way to communicate to replace factoring-based encryption, which quantum computation may one day make insecure. The hype in this article, though, is way over the top. 100 electron spins can only encode 100 classical bits. Not one bit extra. Yablonovitch is using a very sloppy way of talking about how hard it is to simulate 100 spins, and making it sound like he's talking about a way to store a lot of classical bits! His "implicit information storage" is nonsense. It's also worth mentioning that quantum computation is unlikely to speed up any computation you care about, unless you like to simulate quantum systems. Fast factoring is the "killer app" that got people excited about this field, but "terrorists" (and the rest of us) can just stop using factoring-based encryption.

Re:Secure communications?

[bigberk]

if eavesdropping on the encrypted transmission destroys it, couldnt the eavesdropper do so on purpose everytime, effectively jamming all transmission?

Definitely. The main problem with practical quantum crypto communications is this issue of information loss due to noise or tampering. If you could send photons over a lossless link (impossibility) then you guarantee entirely protected communications, or easy detection of tampering/eavesdropping.

But since real transmission lines (even the best optic fibers) will always lose photons, you have to start adding on complicated processing to deal with the losses. Were the photons lost due to natural causes, or is someone eavesdropping? And if data is duplicated to account for losses, the system can possibly be tricked by an attacker into revealing information. This is a delicate subject and a great cause of complication in the field!

The communications can also be jammed of course but the focus of the technology is delivering a secure link.

Re:Article is misleading

[Rich0]

One problem - quantum crypto only works for direct hardware links. It does not allow for retransmission of photons. So, it is limited in range and generally to line of site (or whatever you can reach without reboosted fiber optics).

There is no technology which would allow two distant parties (say 1000 miles apart) to use QC to secure their communication against any evesdropping. There is nothing to suggest that this technology will ever be developed.

Now, with retransmission you could link two arbitrarily distant points. However, you could easiliy intercept the transmission without notice at the repeater. In fact, in most practical implementations, the repeaters are owned by a network provider, who of course would be complying with court orders, etc.

So, QC will prevent cable tapping and stuff like that in the middle of nowhere. However, it will not prevent people with access to the satellites/network closets/etc from intercepting communications.

For all practical purposes, that is no different from not having QC at all. How many communications are intercepted via cable-tapping these days? If you want to intercept something you either get a warrant for an ISP to install Carnivore, or you bribe somebody at the ISP (if you're not legit).

So, QC will not lead to terrorist having secure lines of communication...