In recent years, physicists have been excitedly exploring the potential of an entirely new class of materials known as metamaterials. This stuff is built from repeating patterns of sub-wavelength-sized structures that interact with photons, steering them in ways that are impossible with naturally occuring materials.
The first metamaterials were made from split-ring resonators (C-shaped pieces of metal) the size of dimes that were designed to interact with microwaves with a wavelength of a few centimetres. These metamaterials had exotic properties such as a negative refractive index that could bend light “the wrong way”.
But they were far from perfect, not least because the split-ring resonators introduced losses because of their internal resistance.
It doesn’t take much imagination to think of a solution to this problem: use superconducting resonators that have zero internal resistance.
And that’s a good idea in theory. In practice, however, it is hugely challenging. Apart from the obvious difficulty of operating at superconducting temperatures just above absolute zero, the main problem is that superconducting resonators are quantum devices with strange quantum properties that are fragile and difficult to handle.
In particular, these properties are exponentially sensitive to the physical shape of the resonator. So tiny differences between one resonator and another can lead to huge differences in their resonant frequency.
And since metamaterials are periodic arrays of structures with identical properties, that’s a problem. Indeed, nobody has ever made a quantum metamaterial for precisely this reason.
Today that changes thanks to the work of Pascal Macha at the Karlsruhe Institute of Technology in Germany and a few pals. These guys have built and tested the first quantum metamaterial, which they constructed as an array of 20 superconducting quantum circuits embedded in a microwave resonator.
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