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.
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.
Rare earth ions (REI) in solid materials are among the leading systems for quantum technology applications. However, developing practical REI quantum devices with long-lived coherent states remains challenging due to great difficulties in growing high-quality REI materials and incomplete understanding of their decoherence mechanisms. In this work, we report a long optical coherence time of 422 ± 11 μs for the 7F0 → 5D0 transition, as well as a lifetime exceeding 30 hours for the 7F0 hyperfine spin states in Eu3+:Y2O3 optical ceramics. We identify the absence of two-level-system induced optical decoherence in short-range-ordered crystals and a decoherence mechanism caused by perturbing magnetic centers that were not detected previously below 1.5 K. Furthermore, we demonstrate coherent light storage over 5 μs by using the atomic frequency comb protocol. These results provide a promising proof-of-principle demonstration of quantum memory using Eu3+:Y2O3 optical ceramic system, highlighting its significant potential for practical quantum applications. Rare earth ions (REI) in solids are promising for quantum technologies. Here, the authors demonstrate a record optical coherence lifetime and the absence of two-level-system induced decoherence in Eu3+:Y2O3 optical ceramics. These findings advance the optimization of REI-based quantum systems and enable tailored material designs.
Dense rare-earth spin ensembles in solids offer strong collective light-matter coupling for scalable quantum technologies but are typically incompatible with long coherence times due to strong dipolar interactions. Here we challenge this paradigm by showing long-lived coherence in such systems. In a stoichiometric EuCl_{3}·6H_{2}O crystal, we achieve hyperfine coherence times T_{2}^{CPMG} of up to 15 s at 4 K, extending the zero-field value T_{2} of 1.28 ms by more than four orders of magnitude using dynamical decoupling at a zero-first-order Zeeman (ZEFOZ) transition. Homogeneous linewidth measurements reveal a substantial suppression of resonant Eu^{3+}-Eu^{3+} spin interactions introduced by the full concentration near the ZEFOZ point. Coherence remains resilient to strong local perturbations, with a 32 ms coherence time for Eu^{3+} ions adjacent to Er^{3+} dopants. These results establish stoichiometric rare-earth crystals as a promising platform for quantum memories and spin-photon interfaces, demonstrating that intrinsically high optical depth and long-lived spin coherence can coexist in a fully concentrated ensemble.
Ultralong-lived Coherent States in Eu3+:Y2O3 Optical Ceramics for Quantum Memories
Rare earth ions (REI) in solid materials are among the leading systems for quantum technology applications. However, developing practical REI quantum devices with long-lived coherent states remains challenging due to great growth difficulties of high-quality REI materials and a lack of comprehensive understanding of REI's decoherence mechanisms. Here we realize a record optical coherence time of 421.5 ± 10.5 μs for the 7F0→5D0 transition and more than 30 hours lifetime for the 7F0 hyperfine spin states in Eu3+:Y2O3 optical ceramics. We report the elimination of two-level-system induced optical decoherence in short-range ordered crystals. Meanwhile, a new decoherence mechanism caused by new kinds of perturbing magnetic centers is identified below 1.5 K. We further demonstrate the coherent light storage over 5 μs by using the atomic frequency comb protocol. These results open up prospects for the realization of practical quantum memories and large scale quantum communications with REI optical ceramics.
Rare-earth ion crystals are a promising platform for implementing solid-state quantum interfaces, yet there are few combinations of rare-earth and host crystals that simultaneously deliver large optical absorption, narrow inhomogeneous linewidths, and long coherence times. This work investigates the optical and spin properties of 171Yb3+ ions in YVO4. The observed properties and simple energy-level structure of the 171Yb3+ ion show that this material has significant potential for creating efficient quantum interfaces, such as ensemble-based memories, microwave-to-optical transducers, and optically addressable single rare-earth ion spin qubits.
Rare-earth ion doped crystals possess stable solid state physicochemical properties and long optical coherence time and spin coherence time, thus showing important development prospect in quantum information science and technology area. Investigations on macroscopic bulk rare-earth single crystals have obtained many promising results, especially in the field of optical quantum memory. With the rapid development of quantum information science, a variety of new functions or multifunctional integrations are found in rare earth crystal systems, such as on chip quantum storage, microwave to optical frequency conversion, scalable quantum single photon sources, and quantum logic gates. As a result, beyond the macroscopic bulk rare-earth single crystals, micro/nano-scale rare-earth crystals have received much attention in recent years and they are regarded as promising candidates in highly integrated hybrid quantum systems and miniaturized quantum devices. Moreover, wet chemical method synthesized micro/nano-scale rare-earth crystals have lower growth difficulty and more flexible manipulation in volume, shape and composition. Therefore, exploring high-performance micro/nano-scale rare-earth crystals and precisely manipulating their quantum states have become one of the important directions in today’s quantum information science and technology research. In this review, we first briefly introduce the basic concepts and high resolution spectroscopic techniques that are commonly used in rare earth ion doped crystals for quantum information science and technologies, such as hole burning technique and photon echo technique. Then we summarize comprehensively recent research status and development trends of rare earth ion doped polycrystalline nanoparticles, thin films, single crystal based micro systems, and some other micro/nano-scale rare earth platforms in terms of material fabrication, quantum coherence property, dephasing mechanisms, and also quantum device explorations. The latest research advances in quantum information applications such as quantum storage, quantum frequency conversion, quantum single photon sources and quantum logic gates are given. Finally, we discuss the possible optimization directions and strategies to improve the component design, material synthesis and quantum performance of micro/nano-scale rare earth crystals and their related quantum devices. This review highlights that the micro/nano-scale rare earth crystals may offer many new possibilities for designing quantum light-matter interfaces, thus are promising quantum systems to develop scalable and integrated quantum devices in the future.
The success of the emerging field of solid-state optical quantum information processing (QIP) critically depends on the access to resonant optical materials. Rare-earth ions (REIs) are suitable candidates for QIP protocols due to their extraordinary photo-physical and magnetic quantum properties such as long optical and spin coherence lifetimes (T2). However, molecules incorporating REIs, despite having advantageous properties such as atomically exact quantum tunability, inherent scalability, and large portability, have not yet been studied for QIP applications. As a first testimony of the usefulness of REI molecules for optical QIP applications, we demonstrate in this study that narrow spectral holes can be burned in the inhomogeneously broadened 5D0→7F0 optical transition of a binuclear Eu(III) complex, rendering a homogeneous linewidth (Γh) = 22 ± 1 MHz, which translates as T2=14.5± 0.7 ns at 1.4 K. Moreover, long-lived spectral holes are observed, demonstrating efficient polarization of Eu(III) ground state nuclear spins, a fundamental requirement for all-optical spin initialization and addressing. These results elucidate the usefulness of REI-based molecular complexes as versatile coherent light-spin interfaces for applications in quantum communications and processing.