Waveguide quantum electrodynamics offers a wide range of possibilities to effectively engineer interactions between artificial atoms via a one-dimensional open waveguide. While these interactions have been experimentally studied in the few qubit limit, the collective properties of such systems for larger arrays of qubits in a metamaterial configuration has so far not been addressed. Here, we experimentally study a metamaterial made of eight superconducting transmon qubits with local frequency control coupled to the mode continuum of a waveguide. By consecutively tuning the qubits to a common resonance frequency we observe the formation of super- and subradiant states, as well as the emergence of a polaritonic bandgap. Making use of the qubits quantum nonlinearity, we demonstrate control over the latter by inducing a transparency window in the bandgap region of the ensemble. The circuit of this work extends experiments with one and two qubits toward a full-blown quantum metamaterial, thus paving the way for large-scale applications in superconducting waveguide quantum electrodynamics.

波导量子电动力学为通过一维开放波导有效地设计人工原子之间的相互作用提供了广泛的可能性。尽管已经在少数量子位的限制下对这些相互作用进行了实验研究，但迄今为止，尚未解决此类系统对于超材料配置中的更大量子位阵列的总体属性。在这里，我们通过实验研究了由八个超导跨量子位组成的超材料，其超导频率局部控制与波导的模连续体耦合。通过将量子位连续调谐到一个共同的谐振频率，我们观察到超辐射态和亚辐射态的形成，以及极化子带隙的出现。利用量子位量子非线性，我们通过在集合的带隙区域中引入透明窗口来演示对后者的控制。这项工作的电路将一个和两个量子位的实验扩展到了一个成熟的量子超材料，从而为超导波导量子电动力学的大规模应用铺平了道路。