'Invisibility cloak' revealed as science catches up with fiction

Scientists have built an "invisibility cloak" that can hide everyday objects by splitting light.

It's not quite on a par with Harry Potter's magic garment, but the "cloak", which is actually a lump of calcite crystal, can make objects like pins and paper clips disappear from sight.

Physicists from the University of Birmingham and colleagues from Imperial College, London, and Technical University of Denmark, said using the natural crystal enabled them to hide bigger objects than other researchers.

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The team, led by Dr Shuang Zhang, from the university's school of physics and astronomy, glued two triangular pieces of calcite together, placed on a mirror.

The light enters the calcite and splits into two rays of different polarisations travelling at different speeds and in different directions.

Although the cloak itself is visible, it hides objects placed underneath it.

The researchers said the size of the cloaking area was not limited by the technology available but the size of the crystal and their experiments might pave the way to more devices which can hide much larger objects.

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Dr Zhang said: "This is a huge step forward as, for the first time, the cloaking area is rendered at a size that is big enough for the observer to 'see' the invisible object with the naked eye.

"By using natural crystals for the first time, rather than artificial meta-materials, we have been able to scale up the size of the cloak and can hide larger objects, thousands of times bigger than the wavelength of the light.

"Previous cloaks have succeeded at the micron level (much smaller than the thickness of a human hair) using a nano – or micro-fabricated artificial composite material. It is a very slow process to make these structures and they also restrict the size of the cloaking area.

"We believe that by using calcite, we can start to develop a cloak of significant size that will open avenues for future applications of cloaking devices."

The research has been published in the journal Nature Communications in a paper titled Macroscopic Invisibility Cloak of Visible Light.