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arXiv:2202.08927 · Nature Communications

Emission enhancement of erbium in a reverse nanofocusing waveguide

Nicholas A. Güsken, Ming Fu, Maximilian Zapf, Michael P. Nielsen, Paul M. Dichtl, Robert Röder, Alex S. Clark, Stefan Alexander Maier, Carsten Ronning, Rupert F. Oulton

Published May 11, 2023• 28 citations
arXivHTMLPDF

Abstract

Abstract Since Purcell’s seminal report 75 years ago, electromagnetic resonators have been used to control light-matter interactions to make brighter radiation sources and unleash unprecedented control over quantum states of light and matter. Indeed, optical resonators such as microcavities and plasmonic antennas offer excellent control but only over a limited spectral range. Strategies to mutually tune and match emission and resonator frequency are often required, which is intricate and precludes the possibility of enhancing multiple transitions simultaneously. In this letter, we report a strong radiative emission rate enhancement of Er 3+ -ions across the telecommunications C-band in a single plasmonic waveguide based on the Purcell effect. Our gap waveguide uses a reverse nanofocusing approach to efficiently enhance, extract and guide emission from the nanoscale to a photonic waveguide while keeping plasmonic losses at a minimum. Remarkably, the large and broadband Purcell enhancement allows us to resolve Stark-split electric dipole transitions, which are typically only observed under cryogenic conditions. Simultaneous radiative emission enhancement of multiple quantum states is of great interest for photonic quantum networks and on-chip data communications.

DOI
10.1038/s41467-023-38262-6

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quant-pharXiv:2511.23301•Nature Communications•Dec 1, 2025•0 citations
Abstract Since Purcell’s seminal report 75 years ago, electromagnetic resonators have been used to control light-matter interactions to make brighter radiation sources and unleash unprecedented control over quantum states of light and matter. Indeed, optical resonators such as microcavities and plasmonic antennas offer excellent control but only over a limited spectral range. Strategies to mutually tune and match emission and resonator frequency are often required, which is intricate and precludes the possibility of enhancing multiple transitions simultaneously. In this letter, we report a strong radiative emission rate enhancement of Er 3+ -ions across the telecommunications C-band in a single plasmonic waveguide based on the Purcell effect. Our gap waveguide uses a reverse nanofocusing approach to efficiently enhance, extract and guide emission from the nanoscale to a photonic waveguide while keeping plasmonic losses at a minimum. Remarkably, the large and broadband Purcell enhancement allows us to resolve Stark-split electric dipole transitions, which are typically only observed under cryogenic conditions. Simultaneous radiative emission enhancement of multiple quantum states is of great interest for photonic quantum networks and on-chip data communications.
We report the broadband luminescence enhancement of erbium ions embedded in a non-resonant hybrid waveguide photon-emitter interface on silicon. The measured emission rate enhancement of > 300 is enabled by a large radiative Purcell factor across the spectrum in the telecommunications C-band. This enables the shortening of the lifetime of erbium from 3 ms to 8 μs, effectively providing brighter on-chip photon sources. The platform efficiently collects the photon emission of erbium in a single-mode waveguide and out-couples it to a low-loss photonic waveguide using a reverse nano-focusing method. This hybrid approach opens a large range of possible emitter-waveguide platform combinations for heterogeneous and hybrid quantum emitter integration, towards scalable on-chip quantum networks.
Single quantum emitters coupled to optical cavities in the Purcell regime can be used as high-efficiency spin-photon interfaces that are essential for building a quantum network. Furthermore, the dynamical control of the spontaneous emission rate of quantum emitters can have important implications in quantum technologies, e.g. for shaping the emitted photons waveform, or for driving coherently the optical transition while preventing photon emission. Here we demonstrate the dynamical Purcell-enhanced emission of a mesoscopic ensemble of erbium ions doped into nanocrystals coupled to a fully-tunable high-finesse fiber-based optical microcavity. Erbium has excellent optical and spin coherence properties at cryogenic temperatures and, in addition, has a transition in the telecom band that can facilitate integration into existing commercial telecom fibers. We show that we can tune the cavity on and out of resonance at a rate of above 8 KHz, which is two orders of magnitude faster that the natural lifetime of the erbium ions (55 Hz), and a factor of five faster than the Purcell enhanced emission (1.8 KHz). This allows us to shape in real time the Purcell enhanced emission of the ions and to achieve full control over the emitted photon’s waveforms. With moderate improvements in our detection efficiency and cavity finesse, this capability will allow for the generation of single telecom photons with controllable wave-shape from single erbium ions and for the realization of quantum processing between rare-earth ion qubits using dipolar interactions.
Abstract The interaction of single quantum emitters with an optical cavity enables the realization of efficient spin-photon interfaces, an essential resource for quantum networks. The dynamical control of the spontaneous emission rate of quantum emitters in cavities has important implications in quantum technologies, e.g., for shaping the emitted photons’ waveform or for driving coherently the optical transition while preventing photon emission. Here we demonstrate the dynamical control of the Purcell enhanced emission of a small ensemble of erbium ions doped into a nanoparticle. By embedding the nanoparticles into a fully tunable high finesse fiber based optical microcavity, we demonstrate a median Purcell factor of 15 for the ensemble of ions. We also show that we can dynamically control the Purcell enhanced emission by tuning the cavity on and out of resonance, by controlling its length with sub-nanometer precision on a time scale more than two orders of magnitude faster than the natural lifetime of the erbium ions. This capability opens prospects for the realization of efficient nanoscale quantum interfaces between solid-state spins and single telecom photons with controllable waveform, for non-destructive detection of photonic qubits, and for the realization of quantum gates between rare-earth ion qubits coupled to an optical cavity.
Engineering the local density of states with nanophotonic structures is a powerful tool to control light-matter interactions via the Purcell effect. At optical frequencies, control over the electric field density of states is typically used to couple to and manipulate electric dipole transitions. However, it is also possible to engineer the magnetic density of states to control magnetic dipole transitions. In this work, we experimentally demonstrate the optical magnetic Purcell effect using a single rare earth ion coupled to a nanophotonic cavity. We engineer a new single photon emitter, Er3+^{3+}3+ in MgO, where the electric dipole decay rate is strongly suppressed by the cubic site symmetry, giving rise to a nearly pure magnetic dipole optical transition. This allows the unambiguous determination of a magnetic Purcell factor Pm=1040±30P_m=1040 \pm 30Pm​=1040±30. We further extend this technique to realize a magnetic dipole spin-photon interface, performing optical spin initialization and readout of a single Er3+^{3+}3+ electron spin. This work demonstrates the fundamental equivalence of electric and magnetic density of states engineering, and provides a new tool for controlling light-matter interactions for a broader class of emitters.
Quantum networks and modular quantum computers require efficient spin-photon interfaces, often realized using optical resonators that enhance radiative decay on a desired transition. However, this requires small mode volumes and high quality factors, which limits multiplexing capacity and demands precise frequency tuning. Here, we demonstrate an alternative approach that circumvents these bottlenecks for upscaling. Using a W1 silicon photonic crystal waveguide with a tailored photonic bandgap, we selectively inhibit unwanted decay pathways, thereby redirecting emission to the desired transition. This enables efficient photon collection over a large frequency range, allowing the resolution and individual addressing of tens of erbium dopants. Their lifetimes are preserved, or even increased, compared to bulk material. The extended mode volume of the devices enables the use of lower dopant concentrations, thereby improving emitter coherence. Our approach can be combined with Purcell enhancement and applied to other spin-qubit platforms, opening intriguing perspectives for photonic quantum technologies.