Under the Hood of Quantum Computing

nanotrends writes "Gordie Rose, the CTO of Dwave Systems, the venture funded company that plans to offer paid use of a superconducting quantum computer starting in 2007, reveals secrets of his quantum computer construction. It is based on nobium superconducting 'circuits of atoms' and is not RSFQ. (Rapid Single Flux quantum)."

Re:Advantages?

[Mathinker]

Uhm, from the article, nobody can even assess whether it really is a quantum computer.

"Quantum" computer is misleading

[kestasjk]

What D-Wave has done is begun with the standard approaches to building metal-based processors and modified them in such a way that these processors use quantum mechanics in order to accelerate computation.

Wow, they use quantum mechanics? Every chemical reaction in our universe uses quantum mechanics; they couldn't be more vague if they tried. They're clearly trying to capitalize on the 'quantum computer' buzz.

Woo Woo science

[Valacosa]

A functional quantum computer? Really?

I used to be a undergrad lab assistant. I never worked in quantum computing, but our neighbours were some of these guys [www.iqc.ca]. I picked up a few things, one of those things being that quantum computing is hard.

Classical computers use the laws of classical physics to operate. Classical physics is deterministic, and that's how we want our classical computers to behave. As the chip and die sizes get smaller and smaller (what are we at now, 65nm?) CPUs are more likely to suffer from quantum effects, but AFAIK there's circutry in there to compensate for that. Error checking.

A quantum computer is just a machine that uses the laws of quantum mechanics rather than the laws of classical mechanics to operate. The advantage is that some algorithms, when implemented on a quantum computer, are 2n instead of n^2. I never really understood this, maybe a better physicist will come along and explain it. Anyway, to build a quantum computer one needs two things:
- (a) You need some Quantum bits (qbits) to store data
- (b) You need to get those bits to interact with each other in some fashion

There are many approaches to building a quantum computer. One guy (Raymond Laflamme) has a bunch of different atoms that are different elements all in the same molecule, those interact with each other but he has only developed the ability to read / write to about 5 different qbits. I read about another guy on Slashdot here who made a giant array of qbits using atoms in a laser trap. That gets you a lot of qbits, but they don't interact at all. There are many approaches.

Anyway, the reason I think Dwave Systems is full of bullshit is that any approach thus far is good at (a) or (b), but not both. Someone who got a powerful quantum computer up and running would most assuredly win a Nobel Prize. Also, why the hell would he need to woo venture capital? I know I'm up in Canada, but I'm sure most governments are throwing scads and scads of research money at Quantum computing. Answer? Venture capitalists are more naive.

If there's anything I learned from here [randi.org], it's that a lot of Con artists use buzzwords to try and justify their woo-woo science. "Quantum" is one of them.

Smart money on this guy being a fraud.

Re:Umm yeah right.

[Anonymous Coward]

What would be the point of funding something already useful? Things are funded on the basis of their potential, not on what they can do now.

Re:Advantages?

[Anonymous Coward]

i think you need to relook at your understanding of computers.

Its true, conventional boolean logic computers grow 2^n. But thats because its "bit" is a boolean value, it can only have 2 states, thats where the "2" comes from. A quantom computer would be x^n where x is the number of states a bit can be in, while n is the number of bytes. The articel dosent give any information besides a link to the paper (im to busy), the "12" they spoke of could mean as you took it, to be the number of bits, but that is unimpressive, even current computing technology could have bytes of 12 bits, its easy (altho powers of 2 are better to work with, because of the boolean thing again, 8 bits a byte just happened to work out well). But, since its a quantom computer, i would think it refers to the number of states, which is a lot more then 2, just imagine, 12^8 (8 bit bytes, why not?), take that 128bit computing!

Re:Woo Woo science

[Valacosa]

You're half right. I had forgotten about the quantum properties of transistors.

Though a transister does use Quantum Mechanics to function, it is a discrete unit (a "black box" if you will) with a preidctable outcome. A quantum computer, on the other hand, uses a property of QM known as "superposition of states". A qbit in a quantum computer isn't 0 or 1, but some combination of 0 and 1 at the same time. It's only when the qbit is "observed" (read) that it becomes a 0 or 1.

If we can get these qbits to interact with each other without reading them (or "collapsing the wavefunction", in quantum mechanics lingo) then we can have various superpositions of 0s and 1s interacting with each other within an algoritm. Essentially the algorithm run by the quantum computer is acting in parallel with itself. When we observe the qbits when the algoritm is finished, we see the desired result. I know that sounds like magic, but I've probably explained it poorly. I've explained it better in the past. [uwaterloo.ca]

Incidentially, someone who is uneducated (not stupid, mind you, just uneducated) may have difficulty distinguishing between the BS in the original article and the more scientifically accepted BS I've spouted. See? That's how these con artists are allowed to succeed!

Re:Advantages?

[PatriceVignon]

One of the most interesting categories contains problems that are called NP-complete. These all have the feature that in order to solve the problem all possible solutions must be tried, and the number of possible solutions grows exponentially with the problem size. An example is the Travelling Salesman Problem, although there are literally thousands of them. This category is a particularly interesting target from a commercial perspective because most real-life business problems are in it. ... Quantum computers can be used to get approximate solutions to large NP-complete optimization problems much more quickly than the best known methods running on any supercomputer.

Sorry, but that is simply not true. If you have a classical NP complete problem (e.g. Travelling Salesman), you can solve it by trying out exponentially many steps, 2^n, and most people believe that you cannot find faster (classical) algorithms. With a quantum you can improve this to 2^(n/2) by the so-called Grover search algorithm. This is not nearly enough to make these problems tractable in practice. And to make things worse, this "speed-up" will most likely be eaten up by the necessary error correction.
Lance Fortnow posted a very nice summary of this on his blog: [fortnow.com]

But I'm not a physicist or an engineer and suppose we can overcome these obstacles and actually build a working machine. Then I can imagine the following conversation in 2025:
Quantum People: We now have a working quantum computer.
Public: Yes after 30 years and 50 billion dollars in total funding. What can it do?
Q: It can simulate quantum systems.
P: I'm happy for you. What can it do for the rest of us?
Q: It can factor numbers quickly.
P: Yes, I know. We've had to change all of our security protocols because of your machine. Does factoring have any purpose other than to break codes?
Q: Not really. But we can use Grover's algorithm for general search problems.
P: That sounds great! So we can really solve traveling salesperson and scheduling problems much faster than before?
Q: Not exactly. The quadratic speed-up we get from Grover's algorithm isn't enough the offset the slow-down by using a quantum computer combined with error correction. But we can solve Pell's equation, approximate the Jones polynomial and a few other things very quickly.
P: Are those algorithms particularly useful?
Q: No.
P: They why did you build a quantum computer?
Q: Because we could.

Re:Advantages?

[maxwell demon]

Of course being able to efficiently simulate quantum systems would do a lot for many people. Let's start with quantum chemistry. When you deal with large molecules (as f.ex. in pharmacy), you are basically solving a large quantum system. The basic equations are well known, but the size of the problem is what makes it difficult. A quantum computer could resolve this problem. Or in other words, quantum computers might cause more health for the people.

Or think about material sciences. Again, the basic (quantum) equations are well known, but are too large to calculate directly. Again, a quantum computer might be very helpful. It's hard to say what advantages the new materials might bring us (maybe room-temperature superconductors?), but it's allmost certain that there will be some advantage.