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arXiv:2511.13434 · New Journal of Physics

Optical investigation of ultra-slow spin relaxation in 171 Yb 3+ :Y 2 SiO 5 single crystals

F. Chiossi, Alexey Tiranov, L Nicolas, Diana Serrano, Félix Montjovet-Basset, Eloïse Lafitte-Houssat, Alban Ferrier, Sacha Welinski, Loïc Morvan, Perrine Berger, Alexandre Tallaire, Mikael Afzelius, Philippe Goldner

Published Feb 26, 2026• 0 citations
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Abstract

Abstract We report a detailed investigation of spin relaxation dynamics in the rare-earth-doped crystal 171 Yb:Y 2 SiO 5 , a promising platform for quantum memory based on atomic frequency combs. The population dynamics among the four ground-state hyperfine levels were studied in the 50 mK–6 K temperature range by optically modifying the spin populations and monitoring their return to thermal equilibrium via absorption spectroscopy. Below 1 K, population rethermalization occurs on timescales of several hours and is governed by direct spin-phonon relaxation. In contrast, the lifetime of individual spin states is strongly reduced by spin-spin interactions, ranging from seconds in low-doped (2 ppm) samples to milliseconds at higher doping (10 ppm). These results provide clear guidelines for optimizing doping concentration and operating temperature, indicating that atomic frequency comb lifetimes on the order of one hour are achievable in 171 Yb:Y 2 SiO 5 crystals with Yb concentrations not much lower than 2 ppm and at temperatures at or below 1 K.

DOI
10.1088/1367-2630/ae4acd

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Abstract We report a detailed investigation of spin relaxation dynamics in the rare-earth-doped crystal 171 Yb:Y 2 SiO 5 , a promising platform for quantum memory based on atomic frequency combs. The population dynamics among the four ground-state hyperfine levels were studied in the 50 mK–6 K temperature range by optically modifying the spin populations and monitoring their return to thermal equilibrium via absorption spectroscopy. Below 1 K, population rethermalization occurs on timescales of several hours and is governed by direct spin-phonon relaxation. In contrast, the lifetime of individual spin states is strongly reduced by spin-spin interactions, ranging from seconds in low-doped (2 ppm) samples to milliseconds at higher doping (10 ppm). These results provide clear guidelines for optimizing doping concentration and operating temperature, indicating that atomic frequency comb lifetimes on the order of one hour are achievable in 171 Yb:Y 2 SiO 5 crystals with Yb concentrations not much lower than 2 ppm and at temperatures at or below 1 K.
Optical coherence and spin population dynamics in 171^{171}171Yb3+^{3+}3+:Y2_22​SiO5_55​ single crystals
171^{171}171Yb3+^{3+}3+-doped Y2_22​SiO5_55​ crystals are a promising platform for optical quantum memories in long-distance quantum communications. The relevance of this material lies in 171^{171}171Yb long optical and spin coherence times, along with a large hyperfine splitting, enabling long quantum storage over large bandwidths. Mechanisms affecting the optical decoherence are however not precisely known, especially since low-temperature measurements have so far focused on the 2 to 4 K range. In this work, we performed two- and three-pulse photon echoes and spectral hole burning to determine optical homogeneous linewidths in two 171 Yb:YSO crystals doped at 2 and 10 ppm. Experiments were performed in the 40 mK to 18 K temperature range, leading to linewidths between 320 Hz, among the narrowest reported for rare-earth ions, and several MHz. Our results show that above 6 K the homogeneous linewidth is mainly due to an elastic two-phonon process which results in a slow broadening with temperature, the homogeneous linewidth reaching only 25 kHz at 10 K. At lower temperatures, interactions with 89^{89}89Yb nuclear spin-flips, paramagnetic defects or impurities, and also Yb-Yb interactions for the higher concentrated crystal, are likely the main limiting factor to the homogeneous linewidth. In particular, we conclude that the direct effect of spin and optical excited state lifetime is a minor contribution to optical decoherence in the whole temperature range studied. Our results indicate possible paths and regimes for further decreasing the homogeneous linewidths or maintaining narrow lines at higher 171^{171}171Yb concentration.
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Efficient optical pumping is an important tool for state initialization in quantum technologies, such as optical quantum memories. In crystals doped with Kramers rare-earth ions, such as erbium and neodymium, efficient optical pumping is challenging due to the relatively short population lifetimes of the electronic Zeeman levels, of the order of 100 ms at around 4 K. In this article we show that optical pumping of the hyperfine levels in isotopically enriched 145 Nd :Y 2 SiO 5 crystals is more efficient, owing to the longer population relaxation times of hyperfine levels. By optically cycling the population many times through the excited state a nuclear spin flip can be forced in the ground state hyperfine manifold, in which case the population is trapped for several seconds before relaxing back to the pumped hyperfine level. To demonstrate the effectiveness of this approach in applications we perform an atomic frequency comb memory experiment with 33% storage efficiency in 145 Nd :Y 2 SiO 5 , which is on a par with results obtained in non-Kramers ions, e.g. europium and praseodymium, where optical pumping is generally efficient due to the quenched electronic spin. Efficient optical pumping in neodymium-doped crystals is also of interest for spectral filtering in biomedical imaging, as neodymium has an absorption wavelength compatible with tissue imaging. In addition to these applications, our study is of interest for understanding spin dynamics in Kramers ions with nuclear spin.
Abstract Optical quantum memories are essential components for realizing the full potential of quantum networks. Among these, rare-earth-doped crystal memories stand out due to their large multimode storage capabilities. To maximize the multimode capacity in the time domain, it is key to simultaneously achieve large memory bandwidth and long optical storage time. Here, we demonstrate an atomic frequency comb optical memory in 171 Yb 3+ :Y 2 SiO 5 , with a memory bandwidth of 250 MHz and a storage time of up to 125 µ s. The efficiency reaches 20% at short storage times, and 5% at 125 µ s. These results were enabled by an optimized optical pumping scheme, guided by numerical modelling. Our approach is specifically designed for future spin-wave storage experiments, with the theoretical bandwidth limit set at 288 MHz by the hyperfine structure of 171 Yb 3+ :Y 2 SiO 5 . Additionally, we introduce an efficient method for synthesizing the optical pumping waveforms required for generating combs with tens of thousands of teeth, as well as a simple yet frequency-agile laser setup for optical pumping across a 10 GHz bandwidth.
Abstract The coherent interaction of solid-state spins with both optical and microwave fields provides a platform for a range of quantum technologies, such as quantum sensing, microwave-to-optical quantum transduction and optical quantum memories. Rare-earth ions with electronic spins are interesting in this context. In this work, we use a loop-gap microwave resonator to coherently drive optical and microwave clock transitions simultaneously in a 171 Yb 3+ :Y 2 SiO 5 crystal, achieving a Rabi frequency of 0.56 MHz at 2.497 GHz over a 1-cm long crystal. Furthermore, we provide insights into the spin dephasing at very low fields, showing that superhyperfine-induced collapse of the Hahn echo plays an important role. Our calculations and measurements reveal that the effective magnetic moment can be manipulated in 171 Yb 3+ :Y 2 SiO 5 , which suppresses the superhyperfine interaction at the clock transition. At a doping concentration of 2 ppm and 3.4 K, we achieve spin coherence time of 10.0 ± 0.4 ms.
Abstract Rare-earth ion-doped crystals are of great interest for quantum memories, a central component in future quantum repeaters. To assess the promise of 1 % Tm3+-doped yttrium gallium garnet (Tm:YGG), we report measurements of optical coherence and energy-level lifetimes of its 3H 6 ↔ 3 H4 transition at a temperature of around 500 mK and various magnetic fields. Using spectral hole burning (SHB), we find hyperfine ground-level (Zeeman level) lifetimes of several minutes at magnetic fields of less than 1000 G. We also measure coherence time exceeding one millisecond using two-pulse photon echoes. Three-pulse photon echo and SHB measurements reveal that due to spectral diffusion, the effective coherence time reduces to a few µs over a timescale of around two hundred seconds. Finally, temporal and frequency-multiplexed storage of optical pulses using the atomic frequency comb protocol is demonstrated. Our results suggest Tm:YGG to be promising for multiplexed photonic quantum memory for quantum repeaters.