Photochemical Anchoring of Singly Er3+ Ion-Doped NaYF4 Nanoparticles for Scalable Fabrication of Single-Photon Emitting Devices: Implications for Quantum Light Sources in the Telecom Window
Adriaan L. Frencken, Michael Dobinson, Zohreh Sharifi, Elham Hosseini Toodeshki, Reuven Gordon, Frank C. J. M. van Veggel
Scalable methods to access single-photon sources on demand are highly sought after. As a potential strategy, we demonstrate the optical trapping and chemical anchoring of NaYF 4 nanoparticles (NPs) and NaYF 4 NPs doped with on average a single Er 3+ ion. The anchoring method we present involves surface coating the NPs with thiol-functionalized phospholipids, where the thiol group is protected with a chemical group photoremovable at 340 nm 2-bromo-4′-hydroxyacetophenone. Functionalized NPs are trapped optically in a gold double-nanohole aperture using a 980 nm laser. A 340 nm light beam is focused on the particle, resulting in deprotection of the thiol groups and attachment of the thiols to the gold surface, permanently anchoring the NPs. Electron microscopic imaging proves the successful anchoring after removal of the trapping laser, 340 nm light source, and solvent. The approach is promising for reliably fabricating a single-photon emitting material in a scalable and potentially automatable manner.
Scalable methods to access single-photon sources on demand are highly sought after. As a potential strategy, we demonstrate the optical trapping and chemical anchoring of NaYF 4 nanoparticles (NPs) and NaYF 4 NPs doped with on average a single Er 3+ ion. The anchoring method we present involves surface coating the NPs with thiol-functionalized phospholipids, where the thiol group is protected with a chemical group photoremovable at 340 nm 2-bromo-4′-hydroxyacetophenone. Functionalized NPs are trapped optically in a gold double-nanohole aperture using a 980 nm laser. A 340 nm light beam is focused on the particle, resulting in deprotection of the thiol groups and attachment of the thiols to the gold surface, permanently anchoring the NPs. Electron microscopic imaging proves the successful anchoring after removal of the trapping laser, 340 nm light source, and solvent. The approach is promising for reliably fabricating a single-photon emitting material in a scalable and potentially automatable manner.
Single-photon emitters based on individual atoms or individual atomic-like defects are highly sought-after components for future quantum technologies. A key challenge in this field is how to isolate just one such emitter; the best approaches still have an active emitter yield of only 50% so that deterministic integration of single active emitters is not yet possible. Here, we demonstrate the ability to isolate individual erbium emitters embedded in 20 nm nanocrystals of NaYF 4 using plasmonic aperture optical tweezers. The optical tweezers capture the nanocrystal, whereas the plasmonic aperture enhances the emission of the Er and allows the measurement of discrete emission rate values corresponding to different numbers of erbium ions. Three separate synthesis runs show near-Poissonian distribution in the discrete levels of emission yield that correspond to the expected ion concentrations, indicating that the yield of active emitters is approximately 80%. Fortunately, the trap allows for selecting the nanocrystals with only a single emitter, and so this gives a route to isolating and integrating single emitters in a deterministic way. This demonstration is a promising step toward single-photon quantum information technologies that utilize single ions in a solid-state medium, particularly because Er emits in the low-loss fiber-optic 1550 nm telecom band.
Quantum technologies require sources of single photons, which can be created by isolating individual atoms or ions. Erbium ions are a promising choice for single photon sources as it emits photons at low-loss fiber optic wavelengths. However, erbium has a low emission rate and it is challenging to isolate single emitters reliably. Here, we isolate singly Er3+-doped nanocrystals using optical tweezers in a gold double nanohole aperture. The double nanohole geometry enhances the emission rate from the nanocrystals. With this additional enhancement we observe emission at 1550 nm. Discrete levels of emission from dilutely Er3+-doped nanocrystals are observed—corresponding to the number of active erbium emitters present. Nanocrystals with single active emitters were identified and isolated with this technique, demonstrating a path towards single emitter sources at 1550 nm.
Single-photon sources are required for quantum technologies and can be created from individual atoms and atom-like defects. Erbium ions produce single photons at low-loss fiber optic wavelengths, but they have low emission rates, making them challenging to isolate reliably. Here, we tune the size of gold double nanoholes (DNHs) to enhance the emission of single erbium emitters, achieving 50× enhancement over rectangular apertures previously demonstrated. This produces enough enhancement to show emission from single nanocrystals at wavelengths not seen in our previous work, i.e., 400 and 1550 nm. We observe discrete levels of emission for nanocrystals with low numbers of emitters and demonstrate isolating single emitters. We describe how the trapping time is proportional to the enhancement factor for a given DNH structure, giving us an independent way to measure the enhancement. This shows a promising path to achieving single emitter sources at 1550 nm.
Pulsed Laser Chemical Vapor Deposition (PLCVD) has been used to fabricate single atoms doped nanoparticles of magnesium sulfide. These particles were dispersed in optically transparent Poly-methyl-methacrylate (PMMA) films for near field nano-microscopy such that each nanoparticle doped with a single europium atom falls in the focusing range of the near field microscope. By atomic tailoring, the concentration of the doubly ionized europium, Eu2+, has been maximized in these nanoparticles. The energy and the oscillator strength of the 4f7-4f65d1 electronic transition has been tailored to maximize its addressing by photons in single atom spectroscopy experiments. Results have been presented on the fabrication of these single atom doped nanoparticles and their spectroscopy by laser excited fluorescence technique. Studies of a single Eu2+ ion by confocal micro-spectroscopy are in progress.
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
Defects and dopant atoms in solid state materials are a promising platform for realizing single photon sources and quantum memories, which are the basic building blocks of quantum repeaters needed for long distance quantum networks. In particular, trivalent erbium (Er3+) is of interest because it couples C-band telecom optical transitions with a spin-based memory platform. In order to produce quantum repeaters at the scale required for quantum networks it is imperative to integrate these necessary building blocks with mature and scalable semiconductor processes. In this work, we demonstrate the optical isolation of single Er3+ ions in CMOS-compatible titanium dioxide (TiO2) thin films monolithically integrated on a silicon-on-insulator photonics platform. Our results demonstrate an initial step toward the realization of a monolithically integrated and scalable quantum photonics package based on Er3+ doped thin films.