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.

But quantum mechanics can be used in a variety of practical ways. “To list three which we use regularly: atomic clocks, lasers and transistors,” says Dr Scaife. “Atomic clocks use the signal emitted when atoms in crystals move between discrete energy levels. They’re used as a precise time standard in many things, including GPS navigation.

“Lasers rely on a similar process – the particular discrete energy transition in an atom. The colour/power of a laser depends on the type of atom and the particular transition,” she says.

“Transistors are a type of amplifier ubiquitous in all modern electronics. The principle behind them is based on the fact that electrons in an atom have discrete energy levels and therefore move in different orbits around the nucleus depending on that energy level. The conductivity of a material depends on the electron orbits, and this understanding of conductivity allowed the transistor to be designed.”

So it’s useful and cats are wary of it. But why has quantum mechanics made its way so deeply into popular culture in a way that, say, molecular physics has not?

“Because it sounds cool,” says Dr Scaife. “Because it’s associated with Albert Einstein. Because the very complicated maths behind it can be condensed into pretty accessible thought experiments – like Schrödinger’s cat – that people can understand.”

Then, of course, there are its links with teleportation, an ability second only to being able to fly or be invisible on humanity’s list of wishes they’d ask for from a genie.

Since the 1990s, there have been several successful attempts at “quantum teleportation” – the transmission of a basic unit of quantum information from one location to another. Over the past two decades scientists have been able to demonstrate teleportation in a variety of systems including photons, light fields, nuclear spins, and trapped ions, initially only over a couple of metres.

Over the years, however, the distances have gotten longer and longer: an international research team recently achieved quantum teleportation over a distance of 143km through space. In this case, quantum information – namely, the states of light particles, or photons – was successfully teleported between the Canary Islands of La Palma and Tenerife.

“This was not the transferring of matter,” stresses Dr Shearer. “It was the successful transferring of information.”

Quantum teleportation, therefore, could become a new method of communication – or quantum internet, if you will – particularly for highly sensitive or classified data.

“It’s an enormous deal and could be a way to have unbreakable communications,” says Dr Shearer. “So, for example, if you have encrypted information being transmitted and entangled, it would be impossible for anyone to look at that data and decrypt it.”

Quantum teleportation sends information through free space, rather than on optical fibre. “Any data sent couldn’t be observed by an intercepting party without changing the state of it. In this way, you can ensure that it hasn’t been tampered with. “This is a very practical application of this discovery, and fundamental and theoretical maths and physics were crucial in achieving it,” he says.

Could teleportation of matter become a reality?

SCIENCE-FICTION writers have frequently incorporated the action of making an object or person disintegrate in one place while a perfect replica appears elsewhere. The name given to this is usually teleportation.

Conveniently, they never have to explain how the process works but it is assumed that this type of teleportation would work in a similar way to a 3D fax machine or scanner. Information is scanned and transmitted to another location and used to construct a replica, not necessarily from the material of the original, but possibly from atoms of a similar nature.

The difference between a theoretical teleportation machine and a 3D fax machine or scanner, however, is that the original copy would have to be destroyed in the process, or else things might get very complicated indeed.

“There was a group of scientists in the 1990s who proved that in theory the teleportation of solid objects should be possible,” says Dr Anna Scaife of the University of Southampton. “They used a very well-known quantum mechanical paradox called the Einstein-Podolsky- Rosen (EPR) effect – which Albert Einstein referred to as ‘spooky action at a distance’.

“It was based on a thought experiment where two particles were allowed to interact, but then moved apart in opposite directions. The nature of particles then meant that if you measured the state of one particle, you could infer the exact state of the other without measuring it directly.”

It all sounds highly theoretical but given the recent very real recent quantum teleportation of information over such a long distance, could there ever be a time when we might see the teleportation of matter?

“It’s definitely a step in the right direction,” says Dr Andy Shearer of NUI Galway. “This is the start of the process of understanding how matter could travel through space. But we won’t see anything significant in the next 500 years. At the moment we’re only at the stage of exchanging one or two photons.

“But all these things add up and, more importantly, it will hopefully start a debate on the importance of different fundamental sciences. Quantum mechanics is perceived as a more abstract discipline than most. But if quantum teleportation can lead to a brand new completely secure form of communications, the practical nature of quantum physics will be better recognised and therefore appreciated.”

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