title: Optical Line Width Broadening Mechanisms at the 10 kHz Level in Eu3+:Y2O3Nanoparticles.
abstract: We identify the physical mechanisms responsible for the optical homogeneous broadening in Eu3+:Y2O3nanoparticles to determine whether rare-earth crystals can be miniaturized to volumes less than λ3while preserving their appeal for quantum technology hardware. By studying how the homogeneous line width depends on temperature, applied magnetic field, and measurement time scale, the dominant broadening interactions for various temperature ranges above 3 K were characterized. Below 3 K the homogeneous line width is dominated by an interaction not observed in bulk crystal studies. These measurements demonstrate that broadening due to size-dependent phonon interactions is not a significant contributor to the homogeneous line width, which contrasts previous studies in rare-earth ion nanocrystals. Importantly, the results provide strong evidence that for the 400 nm diameter nanoparticles under study the minimum line width achieved (45 ± 1 kHz at 1.3 K) is not fundamentally limited. In addition, we highlight that the expected broadening caused by electric field fluctuations arising from surface charges is comparable to the observed broadening. Under the assumption that such Stark broadening is a significant contribution to the homogeneous line width, several strategies for reducing this line width to below 10 kHz are discussed. Furthermore, it is demonstrated that the Eu3+hyperfine state lifetime is sufficiently long to preserve spectral features for time scales up to 1 s. These results allow integrated rare-earth ion quantum optics to be pursued at a submicron scale and, hence, open up directions for greater scaling of rare-earth quantum technology.
authors.affiliation: PSL Research University, Chimie ParisTech, CNRS, Institut de Recherche de Chimie Paris , 75005, Paris, France.
authors.forename: John G
authors.identifier: 0000-0003-0780-2471
authors.initials: JG
authors.lastname: Bartholomew
authors.affiliation: PSL Research University, Chimie ParisTech, CNRS, Institut de Recherche de Chimie Paris , 75005, Paris, France.
authors.forename: Karmel
authors.initials: K
authors.lastname: de Oliveira Lima
authors.affiliation: PSL Research University, Chimie ParisTech, CNRS, Institut de Recherche de Chimie Paris , 75005, Paris, France.|Sorbonne Universités , UPMC Université Paris 06, 75005, Paris, France.
authors.forename: Alban
authors.initials: A
authors.lastname: Ferrier
authors.affiliation: PSL Research University, Chimie ParisTech, CNRS, Institut de Recherche de Chimie Paris , 75005, Paris, France.
authors.forename: Philippe
authors.initials: P
authors.lastname: Goldner
keywords: Rare-earth ion doped nanoparticles; coherent spectroscopy; disordered materials; narrow optical transitions; phonon interactions; surface charge fluctuations