Tuesday, September 2, 2008

Quantum Computer Building Block Created

The holy grail of computing might be quantum computing. Exploiting the bizarre ability of microscopic systems to be in a superposition of two exclusive possible states at once, a quantum computer relies on a "quantum bit" to do computation. Unlike an ordinary bit, which can be in a state 0 or state 1, a quantum bit can be in a superposition of 0 and 1. Although when you measure it the result is either 0 or 1, the fact it exists in a superposition in between measurements allows you to do lots of things that are impossible using today's computer technology. In fact, a quantum computer, if it could be built, would be able to do things a computer based on today's design principles could never do, even in principle or how advanced technology became.

One of those things a quantum computer could do is create unbreakable codes. A regular computer could create a code that is very hard to break, and that is what banks, the FBI, and the Defense department do today. But while those codes are hard to break, they could be broken, meaning they aren't completely secure. And it turns out quantum computers would be very good at breaking codes too. The ability to put states in superpositions allows quantum computers to factor numbers quite easily-if only a quantum computer could be built. If you could factor numbers easily you could break anyone's secure code very quickly. So a quantum computer would make today's secure codes obsolete but at the same time give people the ability to achieve total data security.

With that in mind its no surprise that the quest for a quantum computer is on the minds of lots of people. Keeping a quantum bit in a superposition of 0 and 1 for any useful length of time has been a challenge, and researchers have also been concerned about scalability, that is the ability to build a useful computing system out of individual quantum building blocks. One hope for scalability is to build a quantum computer out of semiconductors. This would be done using quantum dots and maybe silicon. The good news is that we already know a lot about manufacturing silicon devices on a large scale.

Recently it was revealed that the news is even better, because researchers figured out a way to make a reasonably stable superposition state for a quantum bit in a semiconductor. They do this by putting a trapped electron in the desired superposition state using lasers. The electron is in a so-called "dark state", meaning it doesn't interact with light and hence the state is stable in regards to additional photon interactions. This would allow researchers to put a quantum bit into a superposition state and keep it there, making quantum computing, including "programming", possible.

It remains to be seen whether this development will really lead to stable, useful quantum computers. Also, what will those computers be able to do when actually built. There has been a lot of hype around this area of research, maybe this development will let us gain a glimpse into the reality of quantum computers.

To learn more about quantum computers, read George Johnson's A Shortcut Through Time.


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goooooood girl said...
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