In a more strict approach, a quantum metamaterial should demonstrate coherent quantum dynamics. Such a system is essentially a spatially extended controllable quantum object that allows additional ways of controlling the propagation of electromagnetic waves.[2][3][4][5][6]
Quantum metamaterials can be narrowly defined as optical media that:[7]
Are composed of quantum coherent unit elements with engineered parameters;
Exhibit controllable quantum states of these elements;
Maintain quantum coherence for longer than the traversal time of a relevant electromagnetic signal.[7][8]
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Felbacq, Didier; Antezza, Mauro (2012). "Quantum metamaterials: A brave new world". SPIE Newsroom. doi:10.1117/2.1201206.004296.
Note: the DOI is linked to a full text article.