Schrödinger's Cat State Might Be Made Macroscopic (Without Harming Cats)

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Schrödinger’s cat is the most famous thought experiment of quantum mechanics. A cat is locked in a box with a poison activated by a quantum process, which is in a superposition of two states. This leads to the entire system being in that state, so (as long as the box is closed) the cat is at the same time both alive and dead.

The thought experiment was set up as a criticism of the main interpretation of quantum mechanics, shining a light on the unclear edge between the classical world and the quantum one. And now physicists might be ready to push the quantum beyond the microscopic and create a macroscopic (visible to the naked eye) Schrödinger’s cat state.

Don’t worry, physicists won’t harm any cats in this attempt. Researchers from the Russian Quantum Center and the University of Calgary are creating superposition states using light. Their technique is reported in Nature Photonics.

Replacing the cat as the object that is in two states with opposite properties, they used light. Two light waves are placed in superposition, with the electromagnetic fields of the waves pointing in opposite directions. This is not too hard to do when the amplitude (intensity of the fields) of the waves is small, but increasing the amplitude in a “classical physics” regime has eluded scientists. Until now.

The team generated an amplified signal by putting two light "cat" states through a beam splitter, producing an entangled state in the two output channels of the apparatus. Measurements showed that they were able to more than double the energy of the newborn "cat" in the output.

"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," lead author Demid Sychev, from the Russian Quantum Center, said in a 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." 

Resolving this question in an experimental manner will have a significant impact in how we imagine and deal with quantum mechanics.

"One of the fundamental questions of physics is the boundary between the quantum and classical worlds," added senior author Professor Alexander Lvovsky, from the University of Calgary and head of the Quantum Optics Laboratory of the Russian Quantum Center. "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 probe it."

Quantum mechanics might seem distant and complicated but its applications are found in most of the technology we use every day. And future technology might be even more overtly quantum.

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