Abstract 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 ion (REI)- based molecular systems, whose quantum properties could be tuned taking advantage of molecular engineering strategies, are one of the systems actively pursued for the implementation of QIP schemes. Herein, we demonstrate the efficient polarization of 2 ground-state nuclear spins—a fundamental requirement for all-optical spin initialization and addressing—in a binuclear Eu(III) complex, featuring inhomogeneously broadened 5D0→7 F0 optical transition. At 1.4 K, long-lived spectral holes have been burnt in the transition: homogeneous linewidth (Γh) = 22 +/- 1 MHz, which translates as optical coherence lifetime (T2opt) = 14.5 +/- 0.7 ns, and ground-state spin population lifetime (T1spin) = 1.6 +/- 0.4 s have been obtained. The results presented in this study are a progressive step towards the realization of molecule-based coherent light-spin QIP interfaces.
Abstract 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 ion (REI)- based molecular systems, whose quantum properties could be tuned taking advantage of molecular engineering strategies, are one of the systems actively pursued for the implementation of QIP schemes. Herein, we demonstrate the efficient polarization of 2 ground-state nuclear spins—a fundamental requirement for all-optical spin initialization and addressing—in a binuclear Eu(III) complex, featuring inhomogeneously broadened 5D0→7 F0 optical transition. At 1.4 K, long-lived spectral holes have been burnt in the transition: homogeneous linewidth (Γh) = 22 +/- 1 MHz, which translates as optical coherence lifetime (T2opt) = 14.5 +/- 0.7 ns, and ground-state spin population lifetime (T1spin) = 1.6 +/- 0.4 s have been obtained. The results presented in this study are a progressive step towards the realization of molecule-based coherent light-spin QIP interfaces.
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.
Coherent light–matter interfaces are key elements for many quantum information processing architectures. Rare-earth ion (REI)-containing systems featuring narrow inter-configurational f–f transitions are suitable for creating such interfaces. Recently, narrow homogeneous linewidths (Γ h ) and long nuclear spin lifetimes ( T 1spin ) associated with two Eu 3+ complexes featuring the 5 D 0 → 7 F 0 f–f transition have been reported, elucidating that REI-molecule-based coherent light–matter interfaces can be obtained. In this study, we report a homogeneous linewidth of 2.8 MHz at 4.2 K, corresponding to an optical coherence lifetime ( T 2opt ) of 114 ns (0.11 μs), associated with the 5 D 0 → 7 F 0 transition of the prototypical charge neutral Eu 3+ complex─[Eu(trensal)]. Moreover, we have observed long nuclear spin lifetimes ( T 1spin ) up to 460 ± 80 s at 4.2 K for the complex and efficient optical pumping of hyperfine levels of the 5 D 0 ground state. The results presented in this study indicate that narrow homogeneous linewidths and long nuclear spin lifetimes could be a generic property of molecular Eu 3+ complexes featuring the 5 D 0 → 7 F 0 transition.
Abstract Coordination complexes of rare‐earth ions (REI) show optical transitions with narrow linewidths enabling the creation of coherent light‐matter interfaces for quantum information processing (QIP) applications. Among the REI‐based complexes, Eu(III) complexes showing the 5D0→7F0 transition are of interest for QIP applications due to the narrow linewidths associated with the transition. Herein, we report on the synthesis, structure, and optical properties of a novel Eu(III) complex and its Gd(III) analogue composed of 2,9‐bis(pyrazol‐1‐yl)‐1,10‐phenanthroline (dpphen) and three nitrate (NO3) ligands. The Eu(III) complex—[Eu(dpphen)(NO3)3]—showed sensitized metal‐centred emission (5D0→7FJ; J=0,1,2,3, 4, 5, or 6) in the visible region, upon irradiation of the ligand‐centred band at 369 nm, with the 5D0→7F0 transition centred at 580.9 nm. Spectral hole‐burning (SHB) studies of the complex with stoichiometric Eu(III) concentration revealed a narrow homogeneous linewidth (Γh) of 1.55 MHz corresponding to a 0.205 μs long optical coherence lifetime (T2opt). Remarkably, long nuclear spin lifetimes (T1spin) of up to 41 s have been observed for the complex. The narrow optical linewidths and long T1spin lifetimes obtained for the Eu(III) complex showcase the utility of Eu(III) complexes as tuneable, following molecular engineering principles, coherent light‐matter interfaces for QIP applications.
Optical interfaces that connect long-lived spin qubits to photons are a central requirement for quantum networking and distributed quantum information processing. Currently, solid-state atomic defects are leading candidates due to their inherent spin and optical coherence. Building on these advancements, synthetically tailored molecular systems represent a fundamental change in the field, utilizing precise atomic control and consistent bottom-up assembly. However, the lack of a robust spin-photon interface combining bright fluorescence, high spectral stability, and the persistent spin lifetimes inherent to ground-state systems has prohibited the detection of individual molecular qubits. Here we show that a triplet ground state carbene molecule, embedded within a structurally matched host crystal, functions as a robust spin-photon interface with single-molecule addressability. The system exhibits narrow zero-phonon lines, spectral stability over more than an hour, spin-selective optical transitions and single-molecule optically detected magnetic resonance. Coherent control yields millisecond-scale dynamical-decoupling coherence and tens-of-milliseconds spin relaxation at a temperature of 4.5 K. These results establish molecular qubits as a viable platform for single-emitter quantum optics while preserving the advantages of bottom-up chemical design and processable materials.
Efforts to harness quantum hardware relying on quantum mechanical principles have been steadily progressing. The search for novel material platforms that could spur the progress by providing new functionalities for solving the outstanding technological problems is however still active. Any physical property presenting two distinct energy states that can be found in a long-lived superposition state can serve as a quantum bit (qubit), the basic information processing unit in quantum technologies. Molecular systems that can feature electron and/or nuclear spin states together with optical transitions are one of the material platforms that can serve as optically addressable qubits. The attractiveness of molecular systems for quantum technologies relies on the fact that molecular structures of atomically defined nature can be obtained in endless diversity of chemical compositions. Crucially, by harnessing the molecular design protocols, the optical and spin (electronic and nuclear) properties of molecules can be tailored, aiding the design of optically addressable spin qubits and quantum sensors. In this contribution, we present a concise and collective discussion of optically addressable spin-bearing molecules - namely, organic molecules, transition metal (TM) and rare-earth ion (REI) complexes - and highlight recent results such as chemical tuning of optical and electron spin quantum coherence, optical spin initialization and readout, intramolecular quantum teleportation, optical coherent storage, and photonic-enhanced optical addressing. We envision that optically addressable spin-carrying molecules could become a scalable building block of quantum hardware for applications in the fields of quantum sensing, quantum communication and quantum computing.
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.