Florian Schreck^1,6 and Andreas Brodschelm^2,†

• ¹Van der Waals-Zeeman Institute, Institute of Physics, University of Amsterdam, Science Park 904, 1098 XH Amsterdam, The Netherlands
• ²Toptica Photonics SE, Lochhamer Schlag 19, 82166 Gräfelfing, Germany
• ³VSL National Metrology Institute, Thijssweg 11, 2629 JA Delft, the Netherlands
• ⁴SURF, Moreelsepark 48, 3511 EP Utrecht, The Netherlands
• ⁵LaserLaB, Department of Physics and Astronomy, Vrije Universiteit Amsterdam, De Boelelaan 1081, 1081 HV Amsterdam, the Netherlands
• ⁶QuSoft, Science Park 123, 1098 XG Amsterdam, The Netherlands

• ^*These authors contributed equally to this work.
• ^†Contact author: NarrowLineComb@strontiumBEC.com