Water bears, similar to the one pictured here, can survive in a vacuum and might be made to behave like quantum objects
Quantum weirdness could soon invade the living world, if a scheme to give a flu virus a strange double life comes off.
In quantum theory, a single object can be doing two different things at once. This so-called "superposition" is a delicate state, destroyed by any contact with the outside world. The largest objects that have been superposed so far are molecules. It is hard to put a much larger object such as a cat or human into a superposition because air molecules and photons are always bouncing off it.
But it might be possible with a small life form, according to Oriol Romero-Isart of the Max Planck Institute for Quantum Optics in Garching, Germany, and his colleagues. They hope to prove the concept with the flu virus, which exhibits some properties of life, because it can survive in a vacuum – solving the problem of pesky air molecules.
Their scheme would use two laser beams, whose light exerts a gentle force on matter. Where the two beams cross they form an "optical cavity" holding the virus in place.
By adjusting the frequency of the beams, the laser photons can be made to absorb the vibration energy of the trapped virus about its centre of mass until it is slowed to its lowest possible energy state. In this "ground state" the virus is ready to go into a superposition.
Sending a laser photon towards the trap should do the trick. Since a photon is a quantum entity it has more than one option open to it. Thus it will be both reflected and transmitted at the trap, putting it into a superposition.
By impinging on the virus, it forces it into a superposition of both its ground state and next vibrational energy state. Now the virus should be doing two different things at once – the equivalent of you simultaneously mowing the lawn and doing the shopping. "They have come up with a really neat experiment – inventive and I think feasible," says Peter Knight of Imperial College London.
Romero-Isart and his colleagues speculate that they could pull off the same feat with a tardigrade, or water bear, an animal less than a millimetre in size that can survive extreme temperatures and a vacuum for several days.
Making a living thing do two things at once is more than a physicist's tour de force. It could answer fundamental questions about the nature of quantum theory.
Most physicists believe that the reason quantum behaviour manifests itself only in small things is that objects are difficult to isolate from their surroundings. But the prominent physicist Roger Penrose of the University of Oxford believes instead that there is a critical size, or mass, at which bodies cease to become quantum.
According to Knight, experiments of the kind proposed by Romero-Isart's team could finally offer a way to distinguish between the mainstream view and Penrose's.