Quantum metamaterials are artificial materials made of quantum coherent elements that can support controllable quantum states while maintaining global coherence whose optical properties are determined by the synergy of the electromagnetic field modes and quantum effects of the constituent atoms. The interest in quantum metamaterials has been particularly fueled by their potential for quantum computing architectures, encompassing the generation and manipulation of quantum states, implementation of quantum gates, and storage of quantum information. The constituent base of quantum metamaterials can include various components such as Josephson junctions, cold atoms, semiconductor quantum dots and wells, solid-state defects, and photonic cavities, plasmonic and two-dimensional layered materials, making a bridge from the developments in fundamental quantum theory to advances in material science. Photonic and polaritonic quantum state engineering with entanglement involving various degrees of freedom, such as polarization and orbital angular momentum, appeals for prospects in on-chip secure quantum communication, ion trapping and quantum computing, and quantum information. Incorporating topological concepts and leveraging machine learning optimization techniques enable the development of highly advanced designs. Besides quantum optics, there are emerging trends in the implementation of quantum metamaterials in the acoustic and phononic domains. They also hold promise in broader application areas, such as energy harvesting to enhance solar cell efficiencies and develop novel thermoelectric materials, as well as in high-sensitivity sensing applications like quantum-enhanced imaging, spectroscopy, and the detection of weak electromagnetic fields. Progress in this field drives innovations in technologies and has the potential to transform industries across multiple sectors.
Guest Editors: Daria Smirnova with APR Editor-in-Chief Chennupati Jagadish.