Metamaterial Superconducting Quantum Circuits
Metamaterials can be used to synthesize an almost magical set of electromagnetic responses, including extreme slowing of the velocity of light, waves which bend (refract) in the `wrong' direction when passing through an interface of two materials, or beams of light which focus rather than spread (diffract) as they propagate forward. One of the more interesting metamaterial examples are those that create frequency bands for which light is entirely forbidden from propagation, a so-called photonic bandgap. Photonic bandgap metamaterials give rise to curious behavior - first considered by Sajeev John some 30 years ago – for atoms embedded inside of them which naturally emit light at frequencies within the bandgap. What happens, for instance, to an excited sodium atom which emits yellow light when it is placed inside a metamaterial with a photonic bandgap covering the visible spectrum? John showed that in this case since the atom cannot radiate light a form of atom-photon bound state is formed in which the atom is attached to a surrounding localized "cloud" (wavepacket) corresponding to a single yellow-wavelength photon.
Besides just the fun of performing fundamental quantum electrodynamics experiments using microwave electrical circuits similar to those found in many of your wireless devices, we believe that superconducting metamaterials may play an important role in future quantum computing technologies and in further studies of more complex quantum systems that lie beyond our capability to model using even the most powerful classical computer simulations. The key - and grand challenge - to unlocking the power and complexity inherent in quantum mechanics theory is to connect vast numbers of qubits together in a structured and organized way while avoiding any unintended coupling to the external environment. Superconducting metamaterials offer, in principle, a scalable and flexible substrate on which to build complex circuit topologies for interconnecting Josephson junction qubits. In a sort of qubit hide and seek game, not only can one play with the spatial arrangement of the connectivity in a metamaterial, but also the frequency-dependence of the connectivity utilizing bandgaps and narrow transmission bands.