Electromagnetic Metamaterials: From Classical to Quantum

Electromagnetic (EM) metamaterials are artificially engineered materials with extraordinary EM properties beyond the limit of existing natural materials; thus, they have been widely used to manipulate the amplitude, phase, polarization, frequency, wave vector, waveform, and other degrees of freedom of EM waves in many practical applications. In this review, we will summarize recent advances in this flourishing field of EM metamaterials, first from the perspectives of the classical regime and then the quantum regime. More specifically, in the classical regime, traditional EM metamaterials are based on effective medium theory, and they have limitations of fixed functionalities and an inability to control EM waves in real time. To overcome these restrictions, information metamaterials, including digital coding and field-programmable metamaterials, have recently been proposed to enable real-time manipulation of EM waves based on the theory of information science. By taking advantage of information metamaterials and artificial intelligence, another crucial milestone of intelligent metamaterials has been achieved in the development of classical metamaterials. After overviewing EM metamaterials in the classical regime, we discuss cutting-edge studies of EM metamaterials in the quantum regime, namely, topological metamaterials and quantum metamaterials. These nonclassical metamaterials show excellent ability to flexibly manipulate the quantum states, and they extend the classical information metamaterials into the field of quantum information science. At the end of this review, we will give some conclusions and perspectives on this fast-evolving field.