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Inorganic Chemistry

Synthesis and Optical Quantum Memory Characterization of α-Eu(IO 3 ) 3 , β-Eu(IO 3 ) 3 , and NaEu(IO 3 ) 4

Jack A. D’Amelio, Nick Kwentus, Amy Tram, Evan Hutson, Ashwith Varadaraj Prabhu, Toby J. Woods, Donny R. Pearson, Elizabeth A. Goldschmidt, Daniel P. Shoemaker

Published Apr 8, 2026• 1 citation
Publisher

Abstract

Three phases of stoichiometric europium(III) iodate compounds are probed as candidates for optical quantum memory to determine the impact of reaction conditions on phase formation and to relate crystal structure to their ability to host persistent excited states relevant to quantum memory. Hydrothermal synthesis procedures for growing macroscopic single crystals of rectangular-block α-Eu(IO 3 ) 3 ( P 2 1 / c ), yellow hexagonal plate β-Eu(IO 3 ) 3 ( P 2 1 / n ), and transparent plate NaEu(IO 3 ) 4 ( Cc ) are presented. The ability to burn narrow and long-lived spectral holes on the 7 F 0 → 5 D 0 optical transitions is a necessary condition for implementing optical quantum memory. α-Eu(IO 3 ) 3 was determined to be incapable of hole-burning due to the presence of insufficient asymmetry of the europium site, which forbids the required optical transition. β-Eu(IO 3 ) 3 was determined to be incapable of storing information due to a lack of observed spectral hole burning, likely due to decoherence caused by the closely packed edge-sharing Eu(III) polyhedra. Analysis of each phase’s crystal structure suggests that the Eu–Eu nearest neighbor distance and distortion of europium site symmetry are critical material design parameters for quantum memory applications.

DOI
10.1021/acs.inorgchem.5c05283

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Three phases of stoichiometric europium(III) iodate compounds are probed as candidates for optical quantum memory to determine the impact of reaction conditions on phase formation and to relate crystal structure to their ability to host persistent excited states relevant to quantum memory. Hydrothermal synthesis procedures for growing macroscopic single crystals of rectangular-block α-Eu(IO 3 ) 3 ( P 2 1 / c ), yellow hexagonal plate β-Eu(IO 3 ) 3 ( P 2 1 / n ), and transparent plate NaEu(IO 3 ) 4 ( Cc ) are presented. The ability to burn narrow and long-lived spectral holes on the 7 F 0 → 5 D 0 optical transitions is a necessary condition for implementing optical quantum memory. α-Eu(IO 3 ) 3 was determined to be incapable of hole-burning due to the presence of insufficient asymmetry of the europium site, which forbids the required optical transition. β-Eu(IO 3 ) 3 was determined to be incapable of storing information due to a lack of observed spectral hole burning, likely due to decoherence caused by the closely packed edge-sharing Eu(III) polyhedra. Analysis of each phase’s crystal structure suggests that the Eu–Eu nearest neighbor distance and distortion of europium site symmetry are critical material design parameters for quantum memory applications.
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We report the optical study of europium nitrate hexahydrate crystals Eu(NO 3 ) ⋅ 3 6H 2 O and their deuterated version Eu(NO 3 ) ⋅ 3 6D 2 O conducted at 50 mK. The crystals show sub-GHz inhomogeneous linewidths for the F 0 7 ↔ 5 D 0 transition and optical coherence times up to 136 μs for the non-deuterated crystal and 750 μs for the deuterated one. In addition, using the spectral hole burning technique, the hyperfine splittings in the absence of an external field have been estimated for the ground and optical levels. These results suggest that rare-earth nitrate crystals could represent a promising class of materials for quantum information applications as well as for fundamental physics experiments requiring narrow optical transitions and good coherence properties. • Deuterated and non-deuterated europium nitrate crystals were grown using the slow-cooling method. • Optical coherence times up to 0.75 ms were measured at 50 mK using the photon echo technique. • Sub-GHz optical inhomogeneous linewidths were observed. • The hyperfine splittings of the ground and optical states were assessed via spectral hole burning.
Materials science has an important role to play in the successful establishment of quantum technologies as they are expected to develop suitable material platforms for these highly demanding applications. Among different promising solid-state materials, rare-earth ions embedded in some host crystals show outstandingly narrow optical line widths and long-lived spin states at cryogenic temperatures. In this manuscript, we explore a promising rare-earth (RE)-based material for use in quantum applications: monazite-phase LaPO 4:Eu 3+ crystals, providing the first comprehensive, high-resolution optical coherence and spin lifetime characterization across the full concentration range, starting from 1% Eu 3+ and up to the fully stoichiometric compound EuPO 4 . The results show optical coherence times of the order 100 μs and nuclear spin lifetimes up to 2 h at 4 K, setting this material among the best reported so far, while experimental conditions for its synthesis with appropriate quality consist of a rather simple solid-state reaction. This opens promising perspectives for its use in quantum applications.
We obtain a low optical inhomogeneous linewidth of 25 MHz in the stoichiometric rare-earth crystal EuCl_{3}·6H_{2}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 ^{153}Eu is spectrally resolved, allowing the whole population of ^{153}Eu^{3+} 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 describe 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.
Stoichiometric materials of Eu(III) offer a promising platform for quantum memories attributable to their unique capability to display a distinctive, nondegenerate 5 D 0 → 7 F 0 transition, which enables precise mapping of optical quantum states into their energy-level manifold─a prerequisite for reliable storage and retrieval on demand. However, placing Eu(III) into chiral polar structures, which are necessary for achieving narrow spectral line widths and long optical lifetimes, is a daunting task. Here, we discover Eu 2 (SeO 3 ) 2 (SO 4 )(H 2 O) 2, a rare Eu(III) material that exhibits chiral polar symmetries encompassing both local and global structures. This unique structure is shaped by an appropriate combination of asymmetric ligands. Chirality fosters dipole–dipole interactions and J -mixing, as evidenced by second-harmonic generation, photoluminescence, and magnetic susceptibility. The broken inversion symmetry is supported by the phase-matching behavior in second-harmonic generation. The 5 D 0 → 7 F 0 transition is observed at 578 nm (2.145 eV) with 7.42 meV line width and 3.39 μs lifetime at T = 78 K. The analysis of magnetic susceptibility data using Van Vleck’s theory results in an effective magnetic moment of ρ eff = 3.33 μ B /Eu 3+ and J -mixing. Heat capacity data reveal underlying phonon dynamics in the material. This study demonstrates a pathway to realizing new chiral stoichiometric Eu 3+ compounds with potential for optically addressable quantum memory applications.