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The first quantum metamaterial raises more questions than it answers

German material scientists have created the world’s first quantum metamaterial. This new material raises more questions than it answers, but it could have significant applications in the realms of single microwave photon detection and phase switching, and as a vehicle for further investigation of the very principles of quantum physics.

A metamaterial, as we covered at length in our feature about wonder materials, is essentially a material that has properties not usually found in nature. In almost all cases, though, when we discuss metamaterials, we’re talking about materials that have a negative refractive index — that bend light in the opposite way to what you’d expect (as per the image at the top of this story). This property of metamaterials allows us to do weird things, such as create invisibility cloaks.
In practice, scientists produce this negative refraction effect with split-ring resonators — basically, two concentric C-shaped pieces of non-magnetic metal (pictured right). The exact method of their operation is beyond the scope of this story, but in essence the shape of the rings, and the location of the gap, affects the frequency that the resonator is tuned to (microwaves, infrared, etc.), and also the refraction of the radiation that hits it. Historically, the main problem with metamaterials based on split-ring resonators is that they only really be tuned to a small range of frequencies, making it hard to create an invisibility cloak that operates across a useful slice of spectrum.

Now, researchers at the Karlsruhe Institute of Technology in Germany have embedded 20 aluminium qubits inside a microwave resonator, creating a very small piece of quantum metamaterial (pictured below). Basically, when microwaves of a certain frequency hit the quantum metamaterial, the photons (which make up the microwaves) bounce around inside the resonator and interact with the 20 qubits, and then eventually leave resonator in a different phase. By measuring the phase change, the researchers came to an interesting conclusion: Up to eight of the qubits were coupling together to affect the photons, and then over time these groups of eight would disassociate into groups of four. We’re not sure why this is, and finding out the answer is prime target for future research.
Beyond the research possibilities, this quantum metamaterial might be used as a photon detector, for phase switching, and some fancy applications such as quantum birefringence and superradiant phase transitions.