Optical quantum memories enable long-distance quantum information distribution, which is critical for establishing the global quantum Internet. Rare-earth qubits are promising candidates due to their spin-optical interfaces with excellent spin coherence and optical properties. When doped into inorganic solids, they display relatively long excited-state lifetimes and, in turn, low storage efficiencies, which are difficult to optimize via material design. Metal–organic frameworks (MOFs) allow fine-tuning of spin coherence and excited-state lifetimes through rational design of coordination environments, thereby offering alternative platforms to host rare-earth qubits. By incorporating Nd 3+ and Yb 3+ into an oxalate-based MOF, we develop frameworks that exhibit spin decoherence time exceeding 5 μs at 3.4 K, near-infrared and/or telecommunication-band photoluminescence, and excited-state lifetimes up to 150 μs. These materials hold promise with long storage times and high storage efficiencies. Spin dynamics analysis reveals design principles to further improve coherence, promoting the development of rare-earth MOFs for quantum information science.
Optical quantum memories enable long-distance quantum information distribution, which is critical for establishing the global quantum Internet. Rare-earth qubits are promising candidates due to their spin-optical interfaces with excellent spin coherence and optical properties. When doped into inorganic solids, they display relatively long excited-state lifetimes and, in turn, low storage efficiencies, which are difficult to optimize via material design. Metal–organic frameworks (MOFs) allow fine-tuning of spin coherence and excited-state lifetimes through rational design of coordination environments, thereby offering alternative platforms to host rare-earth qubits. By incorporating Nd 3+ and Yb 3+ into an oxalate-based MOF, we develop frameworks that exhibit spin decoherence time exceeding 5 μs at 3.4 K, near-infrared and/or telecommunication-band photoluminescence, and excited-state lifetimes up to 150 μs. These materials hold promise with long storage times and high storage efficiencies. Spin dynamics analysis reveals design principles to further improve coherence, promoting the development of rare-earth MOFs for quantum information science.
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.
Metal-organic frameworks (MOFs) have emerged as promising candidates for quantum information and photonic applications due to their structural tunability and the potential to contain molecular qubits in architectures that support coherent light-matter interactions. In this study, we investigate the ultrafast coherent dynamics of a perylene-based MOF, UMCM-313, and its corresponding perylene-based organic linker crystal using time-resolved two-photon near-field scanning optical microscopy (NSOM). By tracking the electronic quantum coherence, we reveal coherent modes persisting up to several hundred femtoseconds (fs) at room temperature and extending to the picosecond regime (≈0.9-1 ps) at 173 K in the MOF, significantly longer than the coherence time observed in the organic linkers at the femtosecond scale. The enhanced electronic coherence of UMCM-313 is attributed to periodic chromophore separation and a reduced degree of homogeneous broadening. Because electron spin coherence can be several orders of magnitude longer than optical coherence, we further probed the spin coherence of photoexcited triplet states in UMCM-313 by using time-resolved and pulsed electron paramagnetic resonance (TREPR and pulse-EPR) spectroscopy. TREPR spectra reveal multiple triplet species within the framework, while pulse-EPR measurements yield a phase memory time of 237 ± 5 ns at 173 K. These results demonstrate that UMCM-313 supports both extended excitonic coherence and nanosecond spin coherence, underscoring the importance of periodic framework connectivity in sustaining phase-stable quantum states. The coexistence of electronic coherence and long-lived spin coherence highlights the potential of MOFs as hybrid platforms for quantum photonic and spintronic technologies capable of maintaining coherence under operationally accessible conditions.
Quantum memories for light are important resources as quantum interfaces between light and matter in future quantum information networks. In particular, solid state optical memories based on rare earth ion doped (REID) crystals are of great interest due to their unique physical properties. They provide large number of atoms naturally trapped in a solid with narrow optical and spin transitions. They indeed have excellent optical and spin state coherence times at cryogenic temperatures. Among the various rare-earth doped materials, Pr3+ :Y 2 SiO 5 crystals have shown excellent properties for light storage and exhibit a level scheme suitable for long lived storage in spin states.
Photonic quantum memories are important devices in quantum information science, and are crucial for several applications including quantum repeaters and quantum networks. Rare-earth (RE) doped crystals are promising candidates as quantum memories for light as they offer coherence properties comparable to those of atomic systems, but free of the drawbacks deriving from atomic motion. The research on RE based quantum memories has been so far mostly focused on the mapping of photonic quantum bits to optical collective excitations, but this leads to short lived and mostly pre-determined storage. However, some RE ions, as Praseodymium and Europium, exhibit the suitable energy level scheme, with three long-lived hyperfine ground states, to enable the spin-wave storage by transferring the collective optical excitations into collective spin excitations. Proof of principle spin-wave quantum memories have been reported in rare-earth doped crystals, using weak coherent states as input [1,2]. Here, I will present our recent results on the realization of multimode spin-wave quantum memories in a Praseodymium doped crystal, using non-classical input light. [1] M. Gündoğan, P. M. Ledingham, K. Kutluer, M. Mazzera and H. de Riedmatten , A solid state spin-wave quantum memory for time-bin qubits, Phys. Rev. Lett. 114, 230501 (2015) [2] P. Jobez, C. Laplane, N. Timoney, N. Gisin, A. Ferrier, P. Goldner, and M. Afzelius, Coherent Spin Control at the Quantum Level in an Ensemble-Based Optical Memory, Phys. Rev. Lett. 114, 230502 (2015)
Interfacing between various elements of a computer--from memory to processors to long range communication--will be as critical for quantum computers as it is for classical computers today. Paramagnetic rare-earth doped crystals, such as Nd(3+):Y2SiO5(YSO), are excellent candidates for such a quantum interface: they are known to exhibit long optical coherence lifetimes (for communication via optical photons), possess a nuclear spin (memory), and have in addition an electron spin that can offer hybrid coupling with superconducting qubits (processing). Here we study two of these three elements, demonstrating coherent storage and retrieval between electron and (145)Nd nuclear spin states in Nd(3+):YSO. We find nuclear spin coherence times can reach 9 ms at ∼5 K, about 2 orders of magnitude longer than the electron spin coherence, while quantum state and process tomography of the storage or retrieval operation between the electron and nuclear spin reveal an average state fidelity of 0.86. The times and fidelities are expected to further improve at lower temperatures and with more homogeneous radio-frequency excitation.
Quantum memories for light are essential components in quantum technologies like long-distance quantum communication and distributed quantum computing. Recent studies have shown that long optical and spin coherence lifetimes can be observed in rare earth doped nanoparticles, opening exciting possibilities over bulk materials, e.g., for enhancing coupling to light and other quantum systems, and material design. Here, we report on coherent light storage in Eu 3+:Y 2 O 3 nanoparticles using the Stark echo modulation memory (SEMM) quantum protocol. We first measure a nearly constant Stark coefficient of 50 kHz/(V/cm) across a bandwidth of 15 GHz, which is promising for broadband operation. Storage of light is then demonstrated with an effective coherence lifetime of 5 μs. Pulses with two different frequencies are also stored, confirming frequency-multiplexing capability, and are used to demonstrate the memory high phase fidelity. These results open the way to nanoscale optical quantum memories with increased efficiency, bandwidth, and processing capabilities.