arXiv subjects

Michael Küblböck

Publications and source records attributed to Michael Küblböck.

3 recordsLinked to original sources

arXiv2026

Generating quantum entanglement from sunlight

Energy consumption is becoming a serious bottleneck for integrating quantum technologies within the existing global information infrastructure. In photonic architectures, considerable energy overheads stem from using lasers, whose high coherence was long considered indispensable for quantum state preparation. Here, we demonstrate that natural, incoherent sunlight can successfully produce quantum-entangled states via spontaneous parametric down-conversion. We detect polarization-entangled photon pairs with a concurrence of $0.905\pm0.053$ and a Bell state fidelity of $0.939\pm0.027$. Importantly, the system violates Bell's inequality with $S=2.5408\pm0.2171$, exceeding the classical threshold of 2, while maintaining generation rates comparable to laser-based setups. These findings pave the way for sustainable quantum applications in resource-limited environments like interplanetary missions.

quant-ph↗

arXiv2026

Solar-pumped Radiation-balanced Laser

Solar-pumped lasers, predominantly based on neodymium gain media, offer a promising route to renewable laser-energy conversion and space-based photonics; however, their performance has been constrained by thermal loading and limited power scalability. Here, we propose and numerically investigate a solar-pumped ytterbium thin-disk gain medium combined with a dome concentrator, which enables multipass solar pumping and enhanced absorption. The design yields comparably low lasing thresholds for neodymium- and ytterbium-doped media, while ytterbium provides superior power scalability, enabling up to threefold higher output power. We further identify ytterbium-doped medium combined with a spherical concentrator as a viable solar-pumped, radiation-balanced configuration, achieving self-cooled lasing at solar pump intensities of 28.5 kW cm-2 within the 1020-1033 nm window of the solar spectrum. We further demonstrate that dual-wavelength pumping overcomes the limitations imposed by low solar intensity and concentration constraints, enabling radiation-balanced lasing at orders-of-magnitude lower solar pump intensities. The proposed spherical-concentrator-based design enhances pump absorption while allowing efficient escape of anti-Stokes fluorescence. These results establish multi-pass, solar-pumped ytterbium lasers as a compact, scalable, and sustainable platform for high-performance solar-pumped lasers.

physics.optics↗

arXiv2026

Microscopic theory of a radiation-balanced solar laser

We develop a microscopic open-quantum-system theory for a radiation-balanced solar laser (RBSL) based on ytterbium-doped yttrium aluminum garnet (Yb:YAG), in which optical gain, thermal redistribution among sublevels of the electronic ground and excited manifolds, and lattice-temperature dynamics are treated within a unified framework. Starting from a Lindblad master equation for a multilevel gain medium coupled to a cavity mode, we include incoherent solar pumping, spontaneous emission, cavity loss, and phonon-assisted intra-manifold relaxation obeying detailed balance. In the regime of fast thermalization within each electronic manifold, a compact temperature-dependent two-level model is derived, in which the gain, inversion, and lasing threshold are controlled by Boltzmann occupation factors and partition functions of the electronic sublevels. This microscopic reduction is then coupled self-consistently to a thermal balance equation accounting for anti-Stokes fluorescence cooling, quantum-defect heating, parasitic absorption, and heat exchange with the environment. The theory predicts several operating regimes, including pure cooling, lasing with net cooling, and lasing with net heating, as well as dynamical effects such as delayed lasing onset induced by self-cooling into threshold. In contrast to earlier radiation-balanced laser (RBL) models based mainly on macroscopic rate equations and thermodynamic balance arguments, the present approach provides a microscopic description of the feedback between quantum optical dynamics and temperature redistribution. It therefore offers a physically transparent framework for analyzing RBSLs and for identifying design strategies that exploit level structure, thermalization, and photonic-environment engineering to stabilize laser operation while minimizing internal heat load.

physics.optics↗