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SYFY WIRE invisible

Invisibility is a power now within reach because of a really bizarre phenomenon 

Invisibility has (almost) gone from fiction to science now that lithium atoms were almost made invisible.

By Elizabeth Rayne
Liz Faceless Hoodie GETTY

Ever wish you could just disappear? That might be possible in the realm of quantum physics.

It might not be enough to make us invisible (yet), but a weird quantum effect that can give matter invisibility powers has finally been proven. The matter itself doesn’t actually vanish (remember that matter can neither be created nor destroyed). For something to be visible, it has to scatter light particles, or photons, but it may be possible to reduce the scattering of light until it reaches zero. There is still something there. You just can’t see it if it scatters no light.

This phenomenon, something H.G. Wells only dreamed of in The Invisible Man, is possible because of the Pauli Exclusion Principle, aka Pauli blocking. If the max number of fermions (atoms with an odd number of electrons, protons, and neutrons) occupy one quantum state, none of them can move to another. This is what an MIT research team, led by Yair Margalit, found out. Their results were recently published in Science (here, here, and here).

“Under regular conditions, when a fermionic atom scatters light, it experiences recoil velocity, like a kick due to absorbing and emitting a photon,” Margalit told SYFY WIRE. “In the ultracold regime, this atom would simply not scatter light as it would under regular conditions.”

It is because of Pauli blocking that an atom which is frozen to extremes can become unable to scatter light and therefore seem invisible. When photons stream through a cloud of atoms, they cause the atoms to bounce off each other, which scatters the photons and makes matter visible to the human eye. That cloud of atoms grows denser and denser as temperatures plummet. Any given atom that was subjected to recoil velocity should be pushed into a different quantum state, but the Pauli Exclusion Principle prevents that. Therefore, they cannot scatter light.

While there are some exceptions — light may still get through atoms at the edges of the cloud or if temperatures aren’t cold enough — photons would not be able to scatter off fermions under the conditions created in the lab. Margalit and his team froze a cloud of lithium atoms down to one hundred thousandth the temperature of interstellar space, and space is freezing as it is. They then used a focus laser to squeeze them to densities at which they had almost no room for light to scatter. The atoms became progressively harder to see in the light of another laser.

“After the atoms scattered light, we measured the heating effect of light scattering on the atoms,” said Margalit. “We then reduced the laser power enough so heating during each pulse was negligible, and we didn't cause any extra effects while measuring the Pauli blocking effect.

Freezing and compressing atoms to the point that they can no longer scatter light could eventually make it impossible to see qubits (quantum bits) of sensitive information that may escape in a quantum computer leak. While it hasn’t been done yet, the researchers believe it is possible that fermions could be made entirely invisible if temperatures are lowered to absolute zero. The experiment made them 38% dimmer, meaning they scattered 38% less light. While there is still 62% to go, Margalit doesn’t think of it as impossible when looking to the future.

"Scattering background light could cause qubits in a quantum computer to lose their fragile quantum state, thus 'leaking out’,” he said. “If qubits were based on fermionic particles, Pauli blocking could prevent them from scattering light, and thus prevent information loss.”