Quantum computing for dummies

Paul Raven @ 27-10-2010

Heard people talking about quantum computing, but not really sure you understand what they mean? Well, you’re far from alone (as the late great Richard Feynman once said, “anyone who claims to understand quantum physics doesn’t understand quantum physics”), but why let that stop you from trying to get a layman’s grasp of the basic ideas?

That, one assumes, is the spirit in which this brief introduction to quantum computing at Silicon.com has been written [via SlashDot]… though I’m in no position to comment on how accurate or useful it is. Input from passing physicists is, as always, more than welcome. 🙂

Hang on, what’s quantum entanglement when it’s at home?

I was afraid you were going to ask. Quantum entanglement is the point where scientists typically abandon all hope of being understood because the thing being described really does defy the classical logic we’re used to.

An object is said to become quantumly entangled when its state cannot be described without also referring to the state of another object or objects, because they have become intrinsically linked, or correlated.

No physical link is required however – entanglement can occur between objects that are separated in space, even miles apart – prompting Albert Einstein to famously dub it “spooky action at a distance”.

The correlation between entangled objects might mean that if the spin state of two electrons is entangled, their spin states will be opposites – one will be up, one down. Entangled photons could also share opposing polarisation of their waveforms – one being horizontal, the other vertical, say. This shared state means that a change applied to one entangled object is instantly reflected by its correlated fellows – hence the massive parallel potential of a quantum computer.

Accuracy aside, what’s interesting to me is seeing this sort of bluffer’s guide in a venue like Silicon.com, which is more of a business organ than a tech one. Prepping the Valley VCs for upcoming investment decisions, perhaps?

Quantum coms?

Aliette de Bodard @ 11-09-2010

Apparently, China has managed to make quantum “teleportation” work, using a blue laser over a range of 16km–thus paving the way for extra-secure communication. Basically, they used entangled particles: every modification to the state of one is reflected instantly in the other.
Pretty darn cool. No idea how close to feasible we are (probably further off than the article implies), but that’s a neat application of quantum physics.

The security of using quantum teleportation to distribute cryptographic keys, on the other hand, is upheld by the laws of physics and has a seemingly infinite time horizon. These keys cannot currently be detected and cracked even with the help of the most powerful computers. Owing to the Heisenberg Uncertainty Principle, the quantum states of photons cannot be observed without changing the state of the particle, which has the result of immediately informing the sender and receiver of any eavesdropping. Quantum communication can thus be used to send the most sensitive information, including keys to decode encrypted data sent over less secure means.

(more on quantum cryptography here at Wikipedia, and here at pcrypto. The last is great, though it’s mostly research papers).

Aliette de Bodard is a Computer Engineer who lives and works in France. When not wrestling with Artificial Intelligence problems (aka teaching computers how to analyse what they see), she writes speculative fiction. She is the author of the Aztec fantasy Servant of the Underworld from Angry Robot, and has had short fiction published in Asimov’s, Interzone and the Year’s Best Science Fiction.