IBM Builds A Limited Quantum Computer

phr1 writes "IBM has announced and Yahoo has noted that the first working implementation of Shor's factoring algorithm. Using NMR techniques they built a seven-qubit quantum computer and factored the number 15 into the factors 3 and 5. This is by far the most complicated quantum computation ever done. It's quite an amazing feat--many people thought quantum computing was just a theoretical curiosity and Shor's algorithm could never be implemented in practice."

Comments

still a long way to go...

[dummkopf]

even though we can factor 15 == 3*5, we are still far away from useful quantum computer applications. the problem is that the coherence time of the atoms is fairly short and only O(10^3) computations can be performed before the system is decoherent. there are many interesting (but rather technical) papers about this subject and how to build quantum computers with quantum dots or any other solid state devices. you can get a glimpse of what is going on at the front of physics at http://xxx.lanl.gov/. just search for quantum+computing...

Unfortunately NMR quantum computing has limits

[Spooky Possum]

The technique used here (NMR) is probably the best understood way of doing quantum computing (a lot of the basics are dragged straight out of medical imaging technology). Unfortunately it has a very fundamental limitation: the initialisation phase scales exponentially. Everything else is practical, but for every qubit you add you need to add exponentially more molecules to your system. Since you start off with a "billion billion" molecules you get a good head start, but systems much beyond seven qubits become very difficult and anything practical is impossible.

Of course almost all current quantum computing schemes have fatal flaws and NMR is well ahead of everyone else (with the possible exception of ion trapping). However in most other schemes the flaws aren't fundamental (just really, really, difficult to fix).

Disclosure: I have worked on a competing quantum computing scheme (neutral atoms). It's crap too.

You Heard It Here First...

[cybrpnk]

Looks like the number of qbits available in a quantum computer is doubling every 18 months. The article notes the 2 qbit computer was built in 1998, the 4 qbit unit in August 2000 and now a 7 qbit computer in December 2001....they've still got another couple of months to get the 8th qbit....

Re:Frightening implications

[KjetilK]

This is an interesting point. We discussed this to some length at the International Conference for Physics Students this summer.

The core question is: Can a real, working quantum computer be built in secrecy?

IMHO, it is very unlikely. It has to do with how science works. A few things can pop out straight from a brilliant idea, and can be implemented based on that idea alone. This is, however, very, very uncommon. Even the most brilliant minds needs feedback from their peers to get anywhere. You need critisism, even strong opposition, to fine-tune your ideas and your arguments. This is what the greater scientific community provides.

In closed projects, even if you hire the best minds, you'll get inbreed, you will not get the same level of critisism, and soon you will most probably paint yourself into a corner.

So, while there are examples of projects that have been developed in secrecy that actually work well, most real science has to be done in the open.

Arguably, the most advanced project that we know of that was conducted in secrecy is the Manhattan project. However, building a nuclear bomb wasn't really that difficult. All the basic science was well understood in 1941, it was just engineering left. The brilliant minds found it rather boring. It was completed, and it was kept secret because of the war, there existed very strong reasons for the people who developed it to keep it secret. Hardly any such reasons exist today. A quantum computer will be so important to science and technology, I don't think you can have a larger group of brilliant minds keep it secret for very long. They would want to have the advancement of science going, and beside, they want the nobel prize.

I'm not really frightened. I'd really like to see quantum computers. Yeah, it will make PKI as we know it obsolote, and it really needs adressing fast. I'm not aware of any algoritms that can make reasonably strong encryption on a classical computer that can withstand an attack from a quantum computer, but we'll need that to be reasonably safe while we're waiting for quantum computers to be widespread enough for everybody to use. Anybody know of efforts in this regard?