Submerged-Shell Atoms Trapped in Noble Gas Solids for Quantum Information and Measurement

This project will perform optical and infrared spectroscopy of neutral thulium atoms trapped in solidified noble gases, which are chemically inert solids sometimes called cryocrystals. The trapped thulium atoms may be excited with a laser, which allows transition frequencies between the atomic energy levels to be measured. Thulium is chosen because of its unusual electron configuration, which contains valence electrons in the f-shell near the nucleus.

Unlike other species whose energy levels are substantially broadened when trapped in a cryocrystal, thulium energy levels are split into resolvable components. This project will employ a new set of spectroscopy techniques to uncover the complete energy level diagram for thulium atoms trapped in solid argon and neon, which paves the way for using their unique properties as probes of the local environment at nanometer scale, or as entangled elements in a quantum device.

The project has great potential for broader impacts to quantum information science and measurement, and will contribute to education of students in surface science, cryogenics, optics, and atomic physics.

This project is motivated in particular from recent observations that the magnetic dipole transition between f shells at 1140 nm can be as narrow as 1.5 GHz, even when averaged over a population. Furthermore, there is no indication of population inhomogeneity at the GHz scale, suggesting that with further cooling, MHz linewidths might be obtained. This is significantly narrower than, for example, the inhomogeneity in diamond NV centers, which supports the notion, seen in gas phase spectroscopy, that submerged f shells interact much less with the surrounding environment than s or p levels.

This suggests a novel platform for quantum information and measurement, where frequency resolution permits detailed optical pumping schemes, even as atoms are held in place at the sub-nanometer scale, co-located with measurement targets, and/or directly integrated into quantum hardware via a universally compatible process requiring a single step: condensing noble gas solids with co-deposition of thulium. In particular, the high density combined with homogeneity are promising for quantum information applications and for observing coherent effects such as superradiance.

To investigate these possibilities, a series of experiments will be performed to determine the low-temperature linewidth of thulium in solid argon and neon hosts, to resolve ground state substructure coming from crystal field splitting, to increase the maximum photon cycling rate, and to attempt to sense the environment near a glass substrate.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.