Design and characterization of rare-earth-activated materials for quantum and classical information processing
Optically resonant materials, particularly rare-earth ions doped into dielectric crystals, are some of the most promising candidates for quantum and classical signal processing applications ranging from highly multi-mode quantum memories to ultra-wide bandwidth RF spectrum analysis and sensing. Specifically, the dynamic interaction of light with the inhomogeneously broadened absorption lines of these materials at cryogenic temperatures provides the unique capability to independently address and manipulate many spectrally distinct subsets of ions in the high-density solid-state environment. As a result, these systems offer unmatched information handling capacities and enable the simultaneous storage and processing of temporal, spectral, polarization, and spatial modes of light by using spectral hole burning and coherent transient methods. This presentation provides an introduction to the unique properties of rare-earth-doped materials that lead to their intrinsic efficiency and storage capacity as well as an overview of active areas of materials research aimed at understanding, optimizing, and ultimately engineering these properties. To realize advances in these applications, we must continue to improve fundamental understanding and practical control of the physical processes that govern ion-ion, ion-spin, and ion-lattice interactions and their effects on decoherence and relaxation phenomena more generally. In particular, we highlight the engineering of lattice defects to manipulate both static disorder (e.g. strain) and dynamic disorder (e.g. magnetic entropy) in crystals and the resulting effects on optical coherence, spectral multiplexing capacity, spin-state lifetimes, and other key parameters. These concepts are applied to specific rare-earth-doped material systems and illustrated by our recent results on quantum memory materials with enhanced properties. Finally, we discuss recent progress on employing single rare-earth ion centers and ion clusters in crystals for quantum information applications.