Quantum metamaterials

A qubit in a transmission line

Now we can finally discuss what kind of structures can be formed using qubits as basic units, and what would be their properties. Consider, for example, the optical properties of such a structure. For wavelengths much larger than the size of a single element, or the distance between elements, the structure will appear to be a continuous material with, possibly, strange properties. Such materials built out of artificial unit blocks are known as metamaterials (e.g., Saleh and Teich, 2007, 5.7) and, indeed, demonstrate such exotic behaviour as having a negative refractive index. Compared to them, quantum metamaterials (Rakhmanov et al., 2008), where the building blocks are qubits (or more complex artificial atoms), which maintain quantum coherence during the characteristic time of the signal propagation through them, and whose quantum state can be, in principle, selectively controlled, promise a wider and even more interesting range of behaviour. Such a device could be called an extended quantum coherent system, and our investigations will take us from the field of already fabricated structures, already conducted experiments and already verified theoretical models and into the even more interesting here-be-dragons territory of suppositions, suggestions and open questions.