Documenting the Coming Singularity

Thursday, May 31, 2007

Shooting Electrons One at a Time: Quantum Computing Comes Closer

It turns out that one of the things you have to do in order to develop a quantum computer is to emit individual electrons from a semiconductor in nanosecond timescales. Here's a brief refresher on what makes quantum computing different from the conventional kind:
Classical computers process information by performing operations on successive "bits", which can be either 0 or 1. Quantum computers, on the other hand, use the phenomenon of entanglement to operate on quantum bits, or "qubits", which can be both 0 and 1 at the same time. The ability to process many values simultaneously should in principle mean that quantum computers can vastly outperform their classical counterparts when performing certain tasks.
Don't know what "entanglement" is?
Quantum entanglement is a quantum mechanical phenomenon in which the quantum states of two or more objects have to be described with reference to each other, even though the individual objects may be spatially separated. This leads to correlations between observable physical properties of the systems. For example, it is possible to prepare two particles in a single quantum state such that when one is observed to be spin-up, the other one will always be observed to be spin-down and vice versa, this despite the fact that it is impossible to predict, according to quantum mechanics, which set of measurements will be observed. As a result, measurements performed on one system seem to be instantaneously influencing other systems entangled with it.
Now that you're all caught up, what's new is that French physicists have developed a way to build a qubit, by "confining electrons to two dimensions in a semiconductor."
Quantum dots have been used as single-electron sources before, but the device made by the French group is the first to be able to emit and absorb electrons over intervals of just a few nanoseconds, which makes the device's speed comparable with present-day electronics. They did this by assuming that the quantum-dot and gate components are analogous to a resistor and capacitor in series, then used RC circuit principles to calculate the combined impedance of the quantum dot and gate, and therefore how frequently electrons would be emitted from the quantum dot given the voltage across the system.
You'll recall that quantum computing is one of the new paradigms that will allow computers to continue their march towards strong AI and consciousness after the laws of physics prevent classical computer chips from getting any smaller or faster.

This development is just another important step in that direction. Stay tuned.

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