Schrodinger’s Alive and Dead Cat Can Also Be in Two Places at Once

Who thought it could get any weirder?

Schrödinger's cat is a well-known thought experiment popularized by brainiac Sheldon Cooper on the hit show The Big Bang Theory. The idea behind it is that a cat is placed in a sealed box with a radioactive source and a poison that will be triggered if an atom of the radioactive substance decays — poor cat!

According to quantum physics, the cat is both alive and dead until someone opens the box, thereby changing its quantum state. Similarly, subatomic particles may be in one state or another. However, they can also be “linked” across space.

With new experiments involving this famous paradox, a Yale University team of scientists has shown that a “quantum cat” can be both alive and dead (quantum superposition), and in two places at once. The study, which has been published in the journal Science, involved inducing photons in two separate cavities to become entangled — where two particles are linked, no matter the distance between them — resulting in the state of one particle instantly influencing the state of the other.

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"This cat is big and smart. It doesn't stay in one box because the quantum state is shared between the two cavities and cannot be described separately," said Chen Wang, a postdoctoral associate at Yale and first author of a study, in a Yale news release. "One can also take an alternative view, where we have two small and simple Schrodinger's cats, one in each box, that are entangled."

The team built a device consisting of two 3D microwave cavities and an additional monitoring port — all connected by a superconducting, artificial atom. In this experiment, the “cat” is made of confined microwave light in both cavities.

By fiddling with the photons in one cavity — assigning them a distinct spin — the researchers were able to give the photons two states, (like the cat, dead or alive), and observed the similar state in photons in the other cavity.

So Schrödinger's cat is alive and dead, and in two places at once.

The research could have applications in quantum computing. According to co-author Robert Schoelkopf, Sterling Professor of Applied Physics and Physics, and director of the Yale Quantum Institute, "It turns out 'cat' states are a very effective approach to storing quantum information [...] Generating a cat in two boxes is the first step."

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