Mainz 2026 – wissenschaftliches Programm

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Q: Fachverband Quantenoptik und Photonik

Q 44: Laser Technology and Applications

Q 44.7: Vortrag

Donnerstag, 5. März 2026, 12:30–12:45, P 2

Heterodyne Interferometry for a Measurement of Vacuum Magnetic Birefringence — •Laura Roberts¹, Aaron Spector², and Todd Kozlowski² — ¹Max-Planck-Institut für Gravitationsphysik (Albert-Einstein-Institut) and Leibniz Universität Hannover, 30167 Hannover, Germany — ²Deutsches Elektronen Synchrotron DESY, 22603 Hamburg, Germany

Vacuum magnetic birefringence (VMB) is a long predicted consequence of quantum electrodynamics which describes the effect where an external magnetic field turns the vacuum into an anisotropic, polarizable medium. Despite more than 40 years of experimental effort, there has yet to be a direct laboratory detection of VMB due to its incredibly small amplitude. The Any Light Particle Search II (ALPS II) at DESY currently operates a string of 24 superconducting HERA dipole magnets, each generating a 5.3 T field, with an effective length of 212 meters, along with a high-finesse optical cavity whose eigenmode propagates through the magnet bore. The ALPS II infrastructure therefore can produce a vacuum birefringence 600 times larger than the previous best VMB search, making its future for VMB promising. We discuss an optical system to perform a measurement of VMB by sensing the differential frequency changes of two orthogonal fields stabilized to resonances of a 246 m long optical cavity whose eigenmode propagates through the ALPS II magnet string. In the following we present the results of implementing a prototype of this scheme on a 19 m cavity and discuss the prospects of the full scale experiment.

Keywords: Interferometry; Vacuum Magnetic Birefringence; Optical Cavity; Frequency Stabilization