Description
Erbium ions in silicon offer a promising route to telecom-compatible quantum photonic interfaces, combining optical transitions in the telecommunications band with access to electron and nuclear spin degrees of freedom. Because the relevant Er transitions arise from intra-4f orbitals that are shielded from the host environment, Er in silicon is expected to retain much of the optical coherence observed in bulk material. However, single Er sites in silicon exhibit homogeneous linewidths on the order of 50 kHz, while the bulk optical lifetime is approximately 1 ms. Reaching the Fourier-transform limit required for indistinguishable single-photon emission therefore demands a reduction of the optical lifetime to the few-microsecond regime. This places a stringent requirement on Purcell enhancement in silicon photonic cavities and is a central benchmark for assessing the feasibility of Er-based quantum photonic devices.
Here, we demonstrate optical lifetime reduction of single Er ions from 1.68 ms to 1.5 μs in silicon nanophotonic cavities, corresponding to more than a 1000-fold enhancement of the total Er emission rate. Accounting for the Er branching ratio, this implies a Purcell factor of approximately 5000. Our devices comprise arrays of 40 photonic crystal cavities with fundamental modes of 0.04 μm³ mode volume and quality factors of 100,000, critically coupled to bus waveguides. By evanescently coupling the bus waveguides to tapered optical fibres, we achieve approximately 50% photon extraction efficiency into optical fibre channels. We tune individual Er ion transitions into resonance with the cavity modes using a magnetic field, enabling detuning-dependent measurements of Purcell enhancement across ions from different Er sites. These results establish state-of-the-art Purcell enhancement for single Er ions in silicon nanophotonic cavities and provide a key step towards fibre-integrated, telecom-band single-photon sources and spin-photon interfaces for quantum communication and information processing.
| I am the presenting author | Yes |
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