Physicists 'Breed' Schrödinger’s Cats To Shed Light On Boundary Between Quantum And Classical Worlds

Nothing exemplifies the weirdness of the quantum realm than Erwin Schrödinger’s famous (or infamous) cat-killing thought experiment. Now, a team of researchers has come up with a technique to “breed” Schrödinger’s cats, and has in the process, figured out a way to create cats with much higher amplitude than ever before.

If that sentence sounded confusing, and if you are wondering how cats can have amplitudes (which, after all, are properties of waves), that’s because your macroscopic brain intuitively rebels against the reality of the subatomic world.

In the original version of the thought experiment, which Schrödinger came up with in 1935 to discredit what he felt were apparent contradictions in the interpretation of quantum mechanics, a cat is trapped in a sealed box along with radioactive material and a vial of poison that will shatter if an atom of the radioactive substance decays. If the laws of quantum physics are extrapolated, they tell us that until someone opens the box, the cat would be in a state of “superposition,” wherein it would be simultaneously alive and dead.

Although this statement seems absurd, it describes a very real behavior that subatomic particles exhibit. In fact, superposition is one of two basic properties of subatomic particles that researchers hope to utilize in building a quantum computer, with the other being quantum “entanglement,” which Albert Einstein once derisively called “spooky action at a distance.”

It is important to note that the cat in this case is not a real one but an analogue for an object in a quantum superposition of two states with opposite properties.

Until now, experiments could only obtain such superpositions at small amplitudes that limited their use. In a new experiment, described in a study published Monday in the journal Nature Photonics, a team of researchers tested a technique that makes it possible to obtain optical “cats” of higher amplitudes with greater success.

This, in turn, could help scientists demarcate the boundary — if there is one — between the quantum world of subatomic particles and the classical (macroscopic) world you and I inhabit.

“The idea of the experiment was proposed in 2003 by the group of Professor Timothy Ralph of the University of Queensland, Australia,” study co-author Anastasia Pushkina from the University of Calgary in Canada, said in a statement. “In essence, we cause interference of two ‘cats’ on a beam splitter. This leads to an entangled state in the two output channels of that beam splitter. In one of these channels, a special detector is placed. In the event this detector shows a certain result, a ‘cat’ is born in the second output whose energy is more than twice that of the initial one.”

Specifically, the researchers succeeded in converting a pair of negative squeezed Schrödinger cat states of amplitude 1.15 to a single positive "cat" of amplitude 1.85. Moreover, they also found that that this procedure can be repeated to create even more enlarged versions.

“New 'cats' can, in turn, be overlapped on a beam splitter, producing one with even higher energy, and so on,” the study’s first author Demid Sychev, a graduate student from the Russian Quantum Center and the Moscow State Pedagogical University, said in the statement. “Thus, it is possible to push the boundaries of the quantum world step by step, and eventually to understand whether it has a limit.”