The development of scalable quantum networks is fundamentally limited by the cryogenic infrastructure required by current solid-state quantum emitters, restricting deployment beyond laboratory settings. Here, we present a computational demonstration of non-cryogenic (277 K) quantum-compatible emission at telecommunication wavelengths from erbium(III) ions embedded in a de novo designed protein scaffold. Building upon our previously proposed "Biological Anchor" architecture for hybrid bio-quantum communication systems3¹, we designed and computationally characterized a chimeric protein, which we term Teledrybin, featuring a modified EF-hand motif optimized for asymmetric 9-coordinate Er³⁺ binding. Using complete active space self-consistent field (CASSCF) calculations with N-electron valence state perturbation theory (NEVPT2) and spin-orbit coupling (SOC), we predict optical transitions at 1554 nm, precisely within the telecommunications C-band (1530–1565 nm). Molecular dynamics simulations at 277 K in H₂O (to be replaced by D₂O on field) demonstrate structural stability over 140 ns, with the Er³⁺ coordination geometry converging to average Er–O distances of 2.34–2.36 Å and angular deviations below 2° across independent AlphaFold3 models. The low-symmetry (C₁) coordination environment enables the otherwise Laporte-forbidden 4f-4f transitions, while the engineered hydrophobic barrier suppresses vibrational quenching by excluding bulk solvent from the binding site—only a single structural D₂O molecule remains coordinated. These results validate the feasibility of protein-based quantum emitters operating under non-cryogenic conditions in the telecom band, offering a biologically-producible, scalable alternative to solid-state quantum light sources for edge-node applications in quantum networks.
The development of scalable quantum networks is fundamentally limited by the cryogenic infrastructure required by current solid-state quantum emitters, restricting deployment beyond laboratory settings. Here, we present a computational demonstration of non-cryogenic (277 K) quantum-compatible emission at telecommunication wavelengths from erbium(III) ions embedded in a de novo designed protein scaffold. Building upon our previously proposed "Biological Anchor" architecture for hybrid bio-quantum communication systems3¹, we designed and computationally characterized a chimeric protein, which we term Teledrybin, featuring a modified EF-hand motif optimized for asymmetric 9-coordinate Er³⁺ binding. Using complete active space self-consistent field (CASSCF) calculations with N-electron valence state perturbation theory (NEVPT2) and spin-orbit coupling (SOC), we predict optical transitions at 1554 nm, precisely within the telecommunications C-band (1530–1565 nm). Molecular dynamics simulations at 277 K in H₂O (to be replaced by D₂O on field) demonstrate structural stability over 140 ns, with the Er³⁺ coordination geometry converging to average Er–O distances of 2.34–2.36 Å and angular deviations below 2° across independent AlphaFold3 models. The low-symmetry (C₁) coordination environment enables the otherwise Laporte-forbidden 4f-4f transitions, while the engineered hydrophobic barrier suppresses vibrational quenching by excluding bulk solvent from the binding site—only a single structural D₂O molecule remains coordinated. These results validate the feasibility of protein-based quantum emitters operating under non-cryogenic conditions in the telecom band, offering a biologically-producible, scalable alternative to solid-state quantum light sources for edge-node applications in quantum networks.
Abstract The development of scalable quantum networks is fundamentally limited by the cryogenic infrastructure required by current solid-state quantum emitters, restricting deployment beyond laboratory settings. Here, we present a computational demonstration of non-cryogenic (277 K) quantum-compatible emission at telecommunication wavelengths from erbium(III) ions embedded in a de novo designed protein scaffold. Building upon our previously proposed "Biological Anchor" architecture for hybrid bio-quantum communication systems 3 ¹, we designed and computationally characterized a chimeric protein, which we term Teledrybin, featuring a modified EF-hand motif optimized for asymmetric 9-coordinate Er³⁺ binding. Using complete active space self-consistent field (CASSCF) calculations with N-electron valence state perturbation theory (NEVPT2) and spin-orbit coupling (SOC), we predict optical transitions at 1554 nm, precisely within the telecommunications C-band (1530–1565 nm). Molecular dynamics simulations at 277 K in H₂O (to be replaced by D₂O on field) demonstrate structural stability over 140 ns, with the Er³⁺ coordination geometry converging to average Er–O distances of 2.34–2.36 Å and angular deviations below 2° across independent AlphaFold3 models. The low-symmetry (C₁) coordination environment enables the otherwise Laporte-forbidden 4f-4f transitions, while the engineered hydrophobic barrier suppresses vibrational quenching by excluding bulk solvent from the binding site—only a single structural D₂O molecule remains coordinated. These results validate the feasibility of protein-based quantum emitters operating under non-cryogenic conditions in the telecom band, offering a biologically-producible, scalable alternative to solid-state quantum light sources for edge-node applications in quantum networks.
Abstract The quest for a scalable quantum internet is fundamentally stalled by the repeater problem, a challenge rooted in the catastrophic fragility of quantum states (decoherence). Current state-of-the-art approaches, based on superconducting circuits, solid-state defects, or photonic memories, are trapped in a trilemma of impossible temperatures, manufacturing, or storage. This paper proposes a radical paradigm shift, abandoning the brute-force engineering of coherence in artificial systems and instead co-opting the principles of the only system known to have mastered it: biological life.Inspired by the long-lasting quantum coherence observed in photosynthetic complexes, we present an engineering roadmap for a room-temperature quantum repeater based on a hybrid bio-quantum architecture. Our "Biological Anchor" protocol leverages the power of de novo protein design to engineer a synthetic molecular "cage," whose excitonic resonance is precisely tuned to the telecommunications C-band wavelength of ~ 1550 nm. This biological "song" acts as a perfect quantum key, mediating the transfer of quantum information from a photon to a guest qubit—a single, shielded Erbium ion—harmonized at a quantum level.
Achieving long lived (μs-scale) quantum coherence at room temperature in the telecom C band remains a central unsolved challenge for solid state quantum platforms, with coherence at this timescale previously demonstrated only under vacuum cryogenic conditions at temperatures over 600 times lower. To this end, we introduce a CMOS-compatible nanoengineering approach that deterministically controls the number of Er ions within a nanoscale volume and their electromagnetic environment using sub 5 nm silicon based hollow nanopillars, which achieves the first deterministic spatial isolation of single erbium ions. This nanostructure-enabled isolation suppresses ion-ion interactions and local electromagnetic field noise, enabling single-erbium-ion operation under ambient conditions. The resulting individually addressable single-ion devices exhibit record room temperature optical coherence times of T2* = ~32 μs in the telecom C-band (limited by the coherence of the laser) and extending to > 100 μs based on photon echo measurements. We further present the first demonstration of background free, upconversion enabled single photon emission from multilevel erbium qudits, providing high contrast coherent optical readout. Beyond these performance gains, our work, through sub-5-nm nanoscale engineering, establishes isolated single-ion environments as a viable route to room-temperature operation for solid-state quantum systems. This approach has the potential to address the long-standing barrier of room-temperature decoherence and open a manufacturable, telecom-compatible pathway toward scalable quantum networks, distributed sensing, and cryogenic-free quantum photonic integrated circuits.
Advancing quantum information science demands solid-state quantum systems that maintain long quantum coherence at elevated temperatures while supporting scalable, CMOS-compatible fabrication and telecom C-band operation. No existing platform has simultaneously achieved these requirements, as state-of-the-art demonstrations of coherent control of erbium ions, with an intrinsic telecom-band optical transition, have been confined to cryogenic temperatures below < 10 K under controlled vacuum conditions. This thesis introduces a new paradigm in which materials science and engineering provides the enabling pathway to quantum coherence. A foundry-compatible nanofabrication approach, paired with targeted materials engineering, is developed to realize a new class of CMOS-scalable quantum system: arrays of spatially isolated single-erbium-ion qudits (five-level systems) embedded in silicon-based (e.g., silicon carbide (SiC) and SiCxOy) hollow nanopillars (HNPs). Non-lithographically defined nanostructure geometries with ≤ 5 nm critical dimensions, achieved through conformal chemical vapor deposition (CVD) with growth rates of ~0.3 Å/s, impose a geometric confinement that self-aligns and spatially isolates individual Er3+ ions with nanometer-scale placement accuracy. Oxygen co-doping during growth introduces Si–C–O defect centers that mediate efficient energy transfer to Er3+ ions, yielding an effective excitation cross section of ~2 × 10−17 cm2, two to three orders of magnitude larger than in bulk crystalline hosts, enabling room-temperature single-ion optical detection without the use of nanophotonic cavities. Within these devices, record-long room-temperature optical quantum coherence in the telecom C-band is demonstrated: T2 = 568 µs via photon echo and T2* = 32 µs via Ramsey interferometry, a performance previously limited to vacuum conditions at temperatures over 900 times lower. Coherent Rabi oscillations are observed with >96% contrast, and pulsed photon-correlation measurements confirm single-photon emission (g2(0) = 0.25) from spatially isolated Er3+ ions at ambient conditions. Furthermore, an upconversion-mediated readout protocol accesses the multi-level qudit structure, producing background-free single-photon emission at 518 nm (g2(0) = 0.06) and 980 nm (g2(0) = 0.18) without the use of an optical cavity, the first such demonstration for erbium. Together, these results establish a materials-driven engineering approach that integrates scalable thin-film growth, nanostructure design, implantation optimization, and quantum-optical characterization, overcoming the fundamental requirement for cryogenic operation in telecom quantum systems. Thus, it establishes a pathway toward revolutionary breakthroughs in cryogenic-free quantum photonic integrated devices for practical, deployable quantum sensing, communication, and networking application
Rare-earth (RE) atoms, such as erbium (Er), have inner-shell optical transitions in the near-infrared, some of which are in the telecom bands. These transitions are largely insensitive to the host environment due to effective shielding by the filled outer shells. Cryogenic rare-gas (RG) solids, such as solid neon (Ne) and argon (Ar), combine high chemical purity with a nearly nuclear-spin-free environment, making them attractive solid hosts for preserving optical and spin coherence. In this work, we isolate neutral Er atoms in solid Ne and Ar at 6 K and characterize their emission by steady-state and time-resolved photoluminescence (PL) spectroscopy. In both hosts, we observe several near-infrared transitions between 1000--1500 nm, including inner-shell emission in the telecom O and E bands. The 4f→5d transition near 1299 nm forms a multiplet of narrow components, consistent with crystal-field splitting, and decays on a microsecond timescale. The 4f→4f transition near 1437 nm shows a matrix shift below 1 cm−1 in both hosts. In solid Ne, its inhomogeneous linewidth is bounded by the spectrometer resolution to < 22 GHz, and its PL lifetime reaches up to 78.9 ms, close to the estimated radiative limit. Thermal annealing extends the 1437 nm lifetime in Ne and suppresses the phonon sidebands relative to the zero-phonon lines in Ar. These results identify RG solids as promising hosts for long-lived telecom-band Er emission and provide a foundation for future spin-photon interfaces and hybrid quantum architectures.
Rare-earth ions in solid-state hosts are a compelling hardware platform for quantum networking due to their exceptional optical, and long-lived spin transitions. Erbium's transitions couple to photons in the Telecom-C band, making it compatible with fibre, and has demonstrated high coherence and low spectral diffusion in a range of materials. However, it has a low optical dipole moment, leading to low light-matter coupling. This limits the rate at which operations performed within a network. Despite decades of research, Er transitions remain poorly understood. Hosts are chosen based on convention, convenience, and (well-informed) heuristics, since calculations of the properties of lanthanide 4f shell are prohibitively difficult. This thesis addresses the challenge of this weak dipole through two complementary approaches; both of which constitute engineering the erbium-crystal system. Firstly, we engineer the emitter itself, from the bottom up. We seek an optimal crystal site for ions, which maintains coherence but increases transition strength. To this end, we have characterised four Er sites in CaF2 to understand how the crystal field affects ion properties. We identify sites with dipole moments as high as 1.63x10^-32 Cm despite lifetimes in excess of 10 ms, and coherence of up to 43.9 µs. This informs our next steps, in selecting an optimal site for single ion addressing, and our long-term goal of designing sites for high dipole moments. In the second approach, we engineer the crystal from the top down, fabricating whispering gallery mode resonators in calcium fluoride. I have fabricated five high Q resonators in doped and undoped CaF2, and commenced their characterisation. We have prototyped a coupler for use of these devices in a cryostat with no free-space optical access. This engineered crystal system - a high dipole erbium site coupled to a high Q resonator - provides a path toward competitive optical cooperativity for single erbium ions in the solid state.