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  • Featured in Physics
  • Open Access

Spectral Stability of Cavity-Enhanced Single-Photon Emitters in Silicon

Johannes Früh1,2,3, Fabian Salamon1,2,3, Andreas Gritsch1,2,3, Alexander Ulanowski1,2,3, and Andreas Reiserer1,2,3,*

  • *Contact author: andreas.reiserer@tum.de
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PRX Quantum 7, 020363 – Published 17 June, 2026

DOI: https://doi.org/10.1103/b974-rt6f

Abstract

The unrivaled maturity of its nanofabrication makes silicon a promising hardware platform for quantum information processing. To this end, efficient single-photon sources and spin-photon interfaces have been implemented by integrating color centers or erbium dopants into nanophotonic resonators. However, the optical emission frequencies in this approach are subject to temporal fluctuations on both long and short timescales, which hinder the development of quantum applications. Here, we investigate this limitation and demonstrate that it can be alleviated by integrating the emitters into Fabry-Perot instead of nanophotonic resonators. Their larger optical mode volume enables both increasing the distance to crystal surfaces and operating at a lower dopant concentration, which reduces implantation-induced crystal damage and interactions between emitters. As a result, we observe a fivefold reduction of the spectral diffusion linewidth down to 4.0(2) MHz. Calculations and experimental investigations of isotopically purified 28Si crystals suggest that the remaining spectral instability is caused by laser-induced electric field fluctuations. In direct comparison with a nanophotonic device, the instability is significantly reduced at the same intracavity power, enabling a tenfold increase of the optical coherence time up to T2=20(1)μs. These findings represent a key step toward spectrally stable spin-photon interfaces in silicon and their potential applications in quantum networking and distributed quantum information processing.

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synopsis

A More Stable Photon Emitter

Published 17 June, 2026

A new device that generates single photons with more consistent wavelengths than existing methods could improve quantum communications.

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Popular Summary

Silicon is best known as the foundation of modern electronics, but it is also emerging as a promising platform for a future quantum internet, which enables users to access remote quantum computers and communicate in a safe and reliable way. A major challenge, however, has been producing single photons from silicon-based quantum emitters with a stable, well-defined color. Tiny fluctuations in the crystal environment can cause the emitted light to drift in frequency, undermining the reliability needed for quantum communication and computing.

Here, we show that implementing a Fabry-Perot resonator with an embedded silicon membrane enables lower dopant concentrations, thereby reducing noise in the crystalline environment while avoiding too-close proximity to interfaces. Compared to earlier nanophotonic devices, this enables a pronounced increase in emitter stability: more than tenfold over short, and fivefold over longer timescales. In effect, frequency fluctuations are reduced to a tolerable level of just a few megahertz. By further study of isotopically purified silicon, nuclear-spin-induced frequency fluctuations are eliminated. This way, laser-induced electric-field noise is identified as the main remaining source of frequency instability. Overall, the presented approach thus brings silicon-based single-photon sources closer to the stability required for practical quantum networks, extending the possibilities for scalable, fiber-compatible quantum technologies.

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PRX Quantum 7, 020363– Published 17 June, 2026
  • Received 20 January 2026
  • Accepted 30 April 2026
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Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.

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