The mainstream scientific community has long asserted that the strange effects of quantum physics, such as quantum indeterminacy and entanglement, can not assert themselves at the classical, or macroscopic, level of everyday physics. In recent years, quantum physicists have been steadily pushing the scale of what can be affected by quantum effects upward, suggesting that large-scale objects can affect, and in turn be affected by distant phenomenon.

A group of physicists at the Okinawa Institute of Science and Technology Graduate University in Japan set out to study the strong-coupling interactions between light and matter — a particular circumstance, typically seen only at the quantum level, where the interactions involved can affect both light and the matter, where under normal conditions the light being observed isn’t affected by the matter it’s interacting with.

The researchers cooled a group of hundreds of millions of electrons to near absolute zero, representing the matter used in the experiment, and introduced them into a cavity that contained microwaves. This allowed the team to measure and observe the interactions that occurred between the electrons and the microwave light.

"We saw strong changes in the electromagnetic wave frequency while they were interacting with the electrons and strong changes in the electrons’ activity as well," explains professor Denis Konstantinov, head of OIST’s Quantum Dynamics Unit. "This is a signature of strong coupling."

The measurements made by Konstantinov’s team allowed them to construct a classical model describing the strong coupling interactions seen in the experiment. Since these otherwise quantum-level interactions were being seen in an otherwise substantial mass of electrons, this suggests that this quantum effect could be scaled up to our everyday, macroscopic world. While the amount of the electrons used in the experiment would still only amount to an extremely microscopic piece of matter, traditional quantum experiments typically employ only a handful of particles, as opposed to the millions of particles present in this experiment.

"The transition from the quantum world to classical behavior is not really clear. But in this case we have shown where the quantum ends and the classical begins," Konstantinov said. "However, while this strong coupling itself is classical, it does not mean that nothing is quantum. You can bring this system to a quantum regime by introducing non-linearity like a qubit." A qubit is a measurement of information, analogous to bits used by computers. "Strong coupling is very important for quantum computing. If you have strong coupling you can exchange quantum information between qubits, light, and particles, which can serve as quantum memory." 

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