Ultra-narrow optical inhomogeneous linewidth in a stoichiometric rare earth crystal

TL;DR

This paper reports achieving an ultra-narrow 25 MHz optical linewidth in a stoichiometric EuCl3.6H2O crystal, enabling advanced quantum memory protocols and the exploration of quantum many-body states in a solid-state system.

Contribution

The study demonstrates a record low inhomogeneous linewidth in a stoichiometric rare earth crystal, enabling hyperfine resolution and new quantum information applications.

Findings

Spectrally resolved hyperfine structure of 153Eu

Implementation of off-resonant Raman memories in solid state

Observation of excitation-induced interactions resembling Rydberg systems

Abstract

We have obtained a low optical inhomogeneous linewidth of 25 MHz in the stoichiometric rare earth crystal EuCl3 .6H2 O by isotopically purifying the crystal in 35 Cl. With this linewidth, an important limit for stoichiometric rare earth crystals is surpassed: the hyperfine structure of 153Eu is spectrally resolved, allowing the whole population of 153Eu3+ ions to be prepared in the same hyperfine state using hole burning techniques. This material also has a very high optical density and can have long coherence times when deuterated. This combination of properties offers new prospects for quantum information applications. We consider two of these, quantum memories and quantum many body studies. We detail the improvements in the performance of current memory protocols possible in these high optical depth crystals, and how certain memory protocols, such as off-resonant Raman memories, can be implemented for the first time in a solid state system. We explain how the strong excitation-induced interactions observed in this material resemble those seen in Rydberg systems, and describe how these interactions can lead to quantum many-body states that could be observed using standard optical spectroscopy techniques.