Superconducting quantum metamaterials extend the idea of their classical counterpart to a regime where their constituent meta-atoms are quantum objects, which can hold their quantum coherence for longer than the propagation time of light through the medium.
In this work, we have realized a quantum metamaterial consisting of eight individually controllable superconducting transmon qubits, which are coupled to the mode continuum of a one-dimensional coplanar waveguide. This system can be described within the framework of waveguide-quantum electrodynamics, which predicates that the mutual interaction of the qubits with the waveguide gives rise to long-range interactions of the qubits.
In spectroscopic measurements we observe the formation of super- and subradiant collective metamaterial excitations, as well as the emergence of a polaritonic band gap and study their dependence on the number of participating resonant qubits. We utilize the collective Autler-Townes splitting of the metamaterial to demonstrate control over its band gap. Furthermore, we exploit the control over the band structure for a first realization of slowly propagating light in the metamaterial. ... mehrOur findings show that superconducting quantum metamaterials are a suitable platform to study fundamental excitations in solids and pave way to applications in quantum information processing like quantum memories.