# Schroedinger’s Cat

When he wasn’t engaging in free love, Erwin Schroedinger was one of the early pioneers of quantum physics. In fact, historians now believe he derived his famous equation during a sexually-charged holiday in the Swiss Alps – quite a colourful character!

But anyway, what about his cat? This was a thought experiment he created in 1935 to demonstrate yet another weird thing about quantum physics. Take a radioactive source, a Geiger counter with a hammer attached, a bottle of poison and a cat. Put them in a box, and arrange them so that the hammer will break the bottle of poison above a certain level of activity from the source. Seal the box, and wait until there is a 50% chance of the cat been dead or alive.

His conclusion was that all the molecules of the cat would be in a superimposition of being dead **AND** alive at the same time, until the box was opened and the cat observed to be in either state. In other words, it’s both dead and alive at the same time. Ow…my head’s spinning from this…

Hey…maybe that’s how zombies appear! They’re alternating between being dead and alive! :p

Okay, back to being serious: the world record has been broken, according to physicsworld.com (one of the magazine sites for the Institute of Physics). Eight photons have been entangled in such a state, instead of the previous record of 6, which was set in 2007.

Now, what is the practical use of this? It has been proposed that this might help quantum computer. Perhaps in about 20 years, quantum computers will replace the digital computers you’re using to read this, or that I’m typing on. They’ve already been built, but are still only experimental: the most complicated calculation they’ve done, to the best of my knowledge, is 5×3 = 15.

Digital computers use binary, or long strings of ones and zeros in base 2: this is the source of the joke “There are 10 types of people in the world: those who understand binary, and those who don’t”. (If you need that explained, 2 in base 10 (what we use in daily life) is 1×2^1 + 0x2^0; 1 0 –> 10.) However, quantum computers aren’t limited to this. They are based on qubits, and a single qubit can be 1, 0, or a quantum superposition of these. Describing the state of *n* qubits requires 2^n complex coefficients – numbers like i, the square root of -1. The result of this, according to Wikipedia’s article on quantum computers is that a 300-qubit computer has a state that is described by 2^300, or 10^90, complex numbers. This is supposedly larger than the number of atoms in the observable universe! That’s going to be hard to crack.

**UPDATE:** A Canadian firm claims to have sold the first commerical quantum computer to American defence firm Lockheed Martin. However, some physicists are sceptical, because they published an experiment involving an 8-qubit device in Nature (Volume 473, Page 194), but they claim they’re selling a 128-qubit device – that’s quite a difference.