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FRI: Friday Contributed Sessions

FRI 12: Quantum Phenomena in Solid-State Devices

FRI 12.2: Vortrag

Freitag, 12. September 2025, 11:00–11:15, ZHG105

X-ray parametric down-conversion reveals EUV-polariton — •Christina Bömer — Deutsches Elektronen-Synchrotron DESY, Hamburg, Germany

Spontaneous parametric down-conversion (PDC) of photons is a gateway into the quantum realm. On the occasion of 100 years of Quantum Physics, we present a study of the effect in the x-ray regime and report the observation of a novel hybrid-state of light and matter that emerges from this fundamental nonlinear process. In our experiment, single x-ray photons are spontaneously converted by a diamond crystal into photon pairs. Of each pair, one photon is tuned to the extreme-ultraviolet (EUV) spectral range, where its coupling to the surrounding diamond is so strong that photonic and electronic properties hybridize: This forms the EUV-polariton. Remarkably, the hybridization occurs without an enhancement cavity, which marks a stark contrast to the prevalent paradigm of strong-coupling in cavities. The EUV-polariton links quantum hybridization in the microscopic domain to meso- and macroscopic length scales via its cavity-free propagation. This offers enticing prospects for studying buried interfaces and nanostructures using the polariton itself as a probe.

Keywords: Spontaneous parametric down-conversion; Nonlinear Scattering; X-ray Quantum Optics; EUV-Polariton; Strong Coupling