A radical difference between the macroscopic world and the microscopic world roots a very important physics question about the limitations of the quantum realm. So, in order to study the boundary between the quantum world and the classical world, physicists have figured out how to 'breed' Schrödinger's cat.

[Image Source: *Wikipedia*]

## What is the Schrödinger's cat experiment?

Schrödinger's cat is a 1935 thought experiment by the German physicist Erwin Schrödinger. It positions a cat in a sealed box and is in a quantum superposition state where it is both dead and alive at the same time. However, when an observer peers into the box, they see the cat either alive or dead, but not both alive and dead. The Copenhagen interpretation of the cat's dead and alive state raises a question of when exactly quantum superposition ends and reality hits one possibility or the other.

Schrödinger designed this theoretical experiment to demonstrate the radical difference between the macroscopic world, one which we are used to, and the microscopic world, one that is controlled by the laws of quantum physics. Moreover, the thought experiment shows how extremely contradicting it is to try and apply quantum concepts to macroscopic scenarios.

## Breeding Schrödinger's Cat

Physicists from the University of Calgary and the Russian Quantum Center has figured out how to breed Schrödinger's cat to study the boundaries between quantum and classical worlds. They have come up with a method for creating quantum superposition states with parameters that can potentially expand beyond microscopic limits. Alexander Lvovsky, the team leader of the research project, explains the purpose of their study.

"One of the fundamental questions of physics is the boundary between the quantum and classical worlds. Can quantum phenomena (provided ideal conditions) be observed in macroscopic objects? Theory gives no answer to this question: maybe there is no such boundary. What we need is a tool that will prove it".

The Schrödinger's cat's physical analog, the two states with opposite properties, provides this desired tool. This is a superposition of two uniform light waves with opposite amplitudes. But it was not previously possible to achieve such superpositions where the terms contained more than four photons. So, the physicists tried to 'breed' such states and have managed to obtain optical 'cats' with randomly high amplitudes. Anastasia Pushnika, a co-author of the experiment, reveals their method in 'breeding' a cat.

"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".

[Image Source: *Russian Quantum Center*]

From the group's experiment, several thousands of Schrodinger's cats were generated and the average number of photons increased from** 1.3 to 3.4.** By iterating the experimental process, in how many times possible, it can reveal if the quantum world has a limit and Demid Sychev, first author of the study, express this great potential of the experiment.

"It is important that the procedure can be repeated: new "cats" can, in turn, be overlapped on a beam splitter, producing one with even higher energy, and so on. Thus, it is possible to push the boundaries of the quantum world step by step, and eventually to understand whether it has a limit".

The group is looking to use the macroscopic Schrödinger's cats for quantum communication technologies and also for quantum computing.

Their paper on this study is published in Nature Photonics.

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