Quantum leaps for mankind

QUANTUM teleportation over a record-breaking distance of 143km through space has just been achieved. Not the kind of teleportation made famous by Star Trek, Dr Who and Quantum Leap, but it is a start.

People will have heard of this branch of science, but most will have only a vague notion of what quantum teleportation means. Its association with the possibility of teleporting objects and even people – “beam me up Scottie” and all that – has led to the term making its way into modern parlance.

“When people talk about making a ‘quantum leap’, they’re usually referring to a big leap or major movement,” says Andy Shearer of NUI Galway. “In fact, the reverse is true: it’s the smallest movement you could make. Quantisation is the smallest possible unit of energy change. It made its way into popular parlance in the 1930s, somehow struck a chord, and this is when people began to use and misuse the term.”

Quantum physics is the study of the universe on very small, atomic, scales. “It gets its name from the fact that on those small scales many quantities that we regard as continuous classically – such as energy – are actually observed to exist in discrete units (ie, quanta) and objects which we would classically describe as individual units can be just as well represented as continuous waves – such as elementary particles,” says Anna Scaife, lecturer in radio astronomy, physics and astronomy at the University of Southampton.

So on very small scales we can’t divide the world into either discrete or continuous: things have a dual nature. This is just one interpretation of quantum theory, known as the Copenhagen interpretation.

“It says that sometimes a particle behaves like a particle and sometimes like a wave,” she says. “If you’re not measuring it, then it’s effectively both – that’s what we mean by ‘wave-particle duality’ – but if you measure it and it behaves like a particle it’s a particle, and if you measure it and it behaves like a wave then it’s a wave. You have defined the state by making the measurement.”

How this duality can exist is illustrated by the famous thought experiment known as Schrödinger’s cat. “If you put a cat in a box with a radioactive source there is a possibility that while in the box the radioactive source will decay and kill the cat, but there is also a possibility that it will not.

“So when the box is closed (ie, you can’t measure the result) the cat is both simultaneously alive and dead, ‘life-death duality’ if you like. It’s only when you open the box and make the measurement that one of the states is realised.”

That is all very well, but if the public were to find out taxpayers’ money was being spent on researchers in labs putting cats into boxes and taking bets as to whether Felix was alive or dead, they’d be less than happy with the return on their investment.