Weekly digest of verified rare-earth-ion results relevant to quantum memories and quantum network interfaces. Each item is labeled Journal (peer reviewed / accepted) or Preprint. Long-form version with full sourcing is on my blog (canonical).
1. Er:YSiO - on-demand ms storage at telecom (Journal, accepted)
Sethia, Gohari Kamel, Oblak (U Calgary), "On-demand millisecond storage of spectrotemporal modes at telecom wavelength", accepted in Phys. Rev. Lett. 30 Sep 2026 (accepted page, preprint arXiv:2512.17181).
Key numbers from the abstract:
- On-demand storage/recall of weak coherent pulses in Er:YSiO up to 1 ms (~10x prior Er demonstrations, per the authors)
- Efficiency 10.36% at 300 us, SNR 10.9, limited mainly by spontaneous emission noise
- Frequency-bin encoding: two spectral modes retrieved with 81.8% overlap
- Multimode: 20 temporal x 3 spectral modes stored simultaneously, selective on-demand recall
Context: telecom-wavelength operation + on-demand + multimode are three boxes a quantum repeater memory needs ticked. Caveats: weak coherent pulses (not single photons), 10% efficiency is far from deployable. What is new this week is peer-review acceptance; the preprint is from Dec 2025.
2. Er:CaWO4 - week-long microwave spectral holes at 10 mK (Journal, 2025; CEA highlight this week)
Wang et al. (CEA/CNRS et al.), "Week-long-lifetime microwave spectral holes in an erbium-doped scheelite crystal at millikelvin temperature", Nat Commun 16, 9032 (2025) (paper), highlighted in CEA news, 26 Oct 2026. Date note: published Oct 2025, publicized now.
- ~3 Er ions per billion atoms in CaWO4 (scheelite), 10 mK, superconducting resonator
- Accumulated echoes measurable after 6 days; slow decay component with ~1 month time constant
- Er resonance drift <10 kHz/month; attributed to a "frozen core" of weakly coupled W nuclear spins
Caveat from the researchers: microwave domain, not optical; stronger spectral modification and ion-resonator coupling needed before any real memory. This is spin-environment stability, not a storage device.
3. Eu-153:Y2SiO5 - coherence enhanced by driving host spins (Journal, accepted)
Nima, Takahashi, Vutha (U Toronto), "Enhanced coherence of rare-earth nuclear spins in a crystal", accepted in Phys. Rev. A 27 Oct 2026 (accepted page, preprint arXiv:2608.03939).
- Nuclear spin coherence of 153Eu3+ in Y2SiO5 significantly enhanced by driving the host crystal's environmental nuclear spins
- Abstract does not quantify the enhancement; application stated is precision measurement (and, by extension, quantum information)
4. Pr:Y2SiO5 - heralded single-photon storage with spin rephasing (Preprint)
Rodriguez-Moldes, Appas, Hanni, Rakonjac, Grandi, de Riedmatten (ICFO), arXiv:2609.02579 (2 Sep 2026).
- First non-classical storage of telecom-heralded single photons in an absorptive memory with spin rephasing: AFC spin-wave protocol + XY4 microwave sequence
- Classical AFC echoes up to ~3 ms
- Non-classical correlations (cavity-enhanced pair source) up to 180 us, cross-correlation 4.6(4)
Caveats: preprint, not peer reviewed; the non-classical regime is 180 us, not 3 ms.
5. Er/Tm/Eu molecular complexes - comparative spectroscopy (Preprint)
Rasekh, Sahil, Mansourzadeh, Galico, Hunger, Murugesu, Oblak, arXiv:2610.27223 (Oct 2026).
- Same ligand, cryogenic spectroscopy across Er3+, Tm3+, Eu3+ complexes
- Spectral hole burning observed only in Eu; no measurable hole in Er or Tm
- Strong laser-induced local heating in Er/Tm powders (recovery seconds to tens of seconds); authors argue heating alone does not explain the contrast - ion-dependent relaxation/decoherence tied to level structure and molecular-environment coupling
- Phonon-mediated broadening via crystal-field levels
Takeaway: ions do not automatically transfer their crystal performance into molecular platforms. Also a useful methodological warning about heating artifacts.
Nd
No new neodymium memory results surfaced this week. Still on the watch list.
Synthesis
Common thread: coherence engineering of the ion's spin environment (frozen core, host-spin driving, XY4 rephasing) rather than optical coherence alone. Storage at telecom is moving from us toward ms with real multiplexing. None of these sources claims a deployable repeater; treat each as incremental, checkable physics.
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