Roger Highfield talks to the British scientists who have found a way to make microscopic objects vanish

It sounds like magic: walls, curtains, even dresses could be rendered transparent by bathing them in a specially crafted beam of light. Rescuers could use the beam to peer through rubble after an earthquake, while doctors could gaze at a damaged lung after making a patient’s skin and ribs vanish.

This remarkable disappearing trick is the kind of sorcery that would grace the pages of a Harry Potter book, yet it is a prediction of real-world science. Magic and science do, after all, have their roots in a fundamental urge to make sense of the world so that we may manipulate it to our own ends. And, in the sense that a wizard is a wise man, they still exist today; wizards (and a few witches) can be seen in the Royal Society, Britain’s national academy of science.

Next week, a team led by Prof Chris Phillips, a quantum conjurer from Imperial College London, will join an elite coven at the Royal Society’s summer exhibition (see below for details), where they will present tantalising evidence of how to make objects disappear. At the flick of a switch, he and his colleague Dr Mark Frogley can make something invisible, albeit just a fraction of a millimetre square of a special material and only for a one ten thousandth of a millionth of a second.

Things are visible because of the way that their atoms interact with a beam of light. When the beam, an electromagnetic wave, hits an atom on this page the electrons in the lowest energy state of the atom absorb the wave’s energy and rise to higher energy levels. Only light of exactly the right colour, the one that corresponds to the energy difference between the two levels, will be absorbed – all other colours pass through.

To show that it is possible to stop absorption from happening, so this light beam can also pass through, Prof Phillips, Dr Frogley and Swiss colleagues at the University of Neuchatel created an idealised atom. They put down single layers of atoms, one at a time, to create specially patterned crystal wafers only a few billionths of a metre deep. These two-dimensional sandwiches, dubbed nanostructures, behave like “artificial atoms”: within them, electrons rattle around in energy levels that are customised to respond in a predictable way to laser light.

In this way, they could exploit an effect predicted by quantum mechanics, the baffling theory that rules the atomic domain: an electron can be prevented from absorbing a particle of laser light and jumping to a higher energy level if a second laser beam is used to link or “couple” the two energy levels to a third one.

To perform this conjuring trick in his lab at Imperial, Prof Phillips uses intense beams of infra-red light from lasers that rely on special semiconductor crystals grown in the former Soviet Union. Although the laser is rated at 10 million w atts, it is surprisingly safe: he encourages me to put my hand in the invisible beam: with each pulse of laser light, I feel a tiny pinprick as some of my skin cells are vaporised.

Using two powerful beams made this way, the team performed its vanishing trick: the artificial atoms became transparent to one beam when a second – coupling – laser illuminated them at the same time. “By shining an invisible powerful laser onto these ‘artificial atoms’, we have learnt how to control the motion of the electrons so they no longer absorb light – when the laser is switched on, the crystals instantly become invisible, only to return to their normal opaque state when the laser is switched off.”

As Prof Phillips says, “we have proved the physics”. Although this was achieved with an idealised material, it suggests that by carefully designing a wand of laser light it may be possible to make anything transparent. “The effect has the potential to lead to all sorts of new applications. You can imagine a laser that works at frequencies we can’t see and, when it shines on your hand, it would open up a transparent hole.”

Called “dressing” by quantum boffins, coupling can do more than stop materials from absorbing light. Turn up the coupling laser and the light passing through an object is amplified. “If you made my hand transparent so I could see something the other side, like your face, I could make it appear brighter and brighter,” he says.

The laws of physics predict that something strange occurs at the same time: as the image brightens, there is a dramatic slowing down, by a factor of almost 40, of the speed of light inside the artificial atom. “This may hold the key to ways of storing and manipulating information in a new and entirely optical way,” says Prof Phillips.

Scientists fantasise about a “quantum computer”, one that is predicted to have stupendous power – if only it could be built. “A quantum computer made from just 1,000 of our nanostructures could perform calculations in a second which would take a normal computer longer than the age of the known universe, so although it will be very difficult, it’s a goal well worth chasing.”
[Posted at: Can They Make You Invisible?]