Through new experiments involving the Schrödinger’s cat state paradox, physicists at Yale University have shown that the famous cat can be in two separate locations at the same time.
Chen Wang and co-authors have given Schrödinger’s cat a second box to play in. Image credit: Michael S. Helfenbein / Yale University.
Schrödinger’s cat, a thought experiment, is a paradox that applies the concept of superposition in quantum physics to objects encountered in everyday life.
The idea 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.
Quantum physics suggests that the cat is both alive and dead, until someone opens the box and, in doing so, changes the quantum state.
This experiment, envisioned by Austrian physicist Erwin Schrödinger in 1935, has found vivid analogies in labs in recent years.
Yale physicists created a more exotic type of Schrödinger’s cat-like state that has been proposed for experiments for more than two decades.
This cat lives or dies in two boxes at once, which is a marriage of the idea of Schrödinger’s cat and another central concept of quantum physics: entanglement (entanglement allows a local observation to change the state of a distant object instantaneously).
The team, led by Chen Wang of Yale’s Department of Applied Physics and Physics, took two separate spatial cavities and applied light waves in such a way that only one wavelength may exist in the cavities at a time, giving the two spatially separated areas similar qualities.
The two cavities were joined by a supercurrent, a current that flows without any voltage applied.
The scientists then subjected photons in one cavity to a maze of gates that gave them a distinct spin.
This way, they were able to give the photons two states (like the Schrödinger’s cat, dead or alive), and they observed the similar state in photons in the adjoining cavity.
So far, the team has measured ‘cat sizes’ of up to 80 photons, and larger sizes can be achieved by implementing specially controlled pulses.
“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,” Wang said.
“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 research, published in the journal Science, also has potential applications in quantum computation.
A quantum computer would be able to solve certain problems much faster than classical computers by exploiting superposition and entanglement. Yet one of the main problems in developing a reliable quantum computer is how to correct for errors without disturbing the information.
“It turns out ‘cat’ states are a very effective approach to storing quantum information redundantly, for implementation of quantum error correction,” said co-author Prof. Robert Schoelkopf.
“Generating a cat in two boxes is the first step towards logical operation between two quantum bits in an error-correctible manner.”
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Chen Wang et al. 2016. A Schrödinger cat living in two boxes. Science, vol. 352, no. 6289, pp. 1087-1091; doi: 10.1126/science.aaf2941
