Phys.org's April 15, 2022 Ancient Namibian stone could hold key to future quantum computers begins:
A special form of light made using an ancient Namibian gemstone could be the key to new light-based quantum computers, which could solve long-held scientific mysteries, according to new research led by the University of St Andrews.
The research, conducted in collaboration with scientists at Harvard University in the US, Macquarie University in Australia and Aarhus University in Denmark and published in Nature Materials, used a naturally mined cuprous oxide ($\require{mhchem} \ce{Cu_2O}$) gemstone from Namibia to produce Rydberg polaritons, the largest hybrid particles of light and matter ever created.
and links to Orfanakis et al. (2022) in Nature Materials Rydberg exciton–polaritons in a $\ce{Cu_2O}$ microcavity (also available at ohadi.group). The abstract:
Giant Rydberg excitons with principal quantum numbers as high as $n=25$ have been observed in cuprous oxide ($\ce{Cu_2O}$), a semiconductor in which the exciton diameter can become as large as ∼1 μm. The giant dimension of these excitons results in excitonic interaction enhancements of orders of magnitude. Rydberg exciton–polaritons, formed by the strong coupling of Rydberg excitons to cavity photons, are a promising route to exploit these interactions and achieve a scalable, strongly correlated solid-state platform. However, the strong coupling of these excitons to cavity photons has remained elusive. Here, by embedding a thin $\ce{Cu_2O}$ crystal into a Fabry–Pérot microcavity, we achieve strong coupling of light to $\ce{Cu_2O}$ Rydberg excitons up to n = 6 and demonstrate the formation of $\ce{Cu_2O}$ Rydberg exciton–polaritons. These results pave the way towards realizing strongly interacting exciton–polaritons and exploring strongly correlated phases of matter using light on a chip.
Question: How can an $n=25$ Rydberg state exist in a solid? What does the wave function look like?
I normally think of Rydberg atoms and Rydberg states in general as existing only at atoms (or hydrogen atom-like1 systems e.g. muonium) quite well isolated from perturbations, so usually in vacuum (in astrophysics and in the laboratory) and often cooled in an atomic trap of some kind, rather than inside a solid.
This is an exciton which is still a hydrogen-like fixed positive charge with a bound negative charge with a large wave function. Wikipedia's Wannier–Mott exciton; Equations for 3D semiconductors doesn't have too much to say about such a high level of excitation or details of the wave function.
As to "What does the wave function look like?" I would expect it to be overall spherical in nature, but is it corrugated by the Bloch potential of the crystal lattice in some way?
1cf. this answer to What is a "hydrogen-like" or "hydrogenic" atom?
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