arXiv subjects

Stefan Kazmaier

Publications and source records attributed to Stefan Kazmaier.

3 recordsLinked to original sources

arXiv2025

Achieving precision in measuring birefringence characteristics of a periodically-poled Lithium Niobate waveguide

The refraction of light in an optical medium is not only a subject of fundamental interest, but the refractive index also plays a crucial role in applications involving integrated and non-linear optics. One such application is photon-pair generation in waveguides with second-order nonlinearity. The spectral properties of the generated photon pairs are governed by the effective group refractive indices of the interacting modes, which normally are calculated via Sellmeier's equations for bulk crystals. However, in integrated optics, the effective group refractive indices experienced by the propagating modes can differ from those in bulk materials. Therefore, we present an accurate, in-situ measurement technique for determining the birefringence characteristics of a structure with high reflective end facets by performing a Fourier transformation of the light transmission spectrum and apply this method to a periodically-poled Lithium Niobate waveguide resonator in the telecom wavelength range. We directly predict important spectral figures of merit of the photon-pair generation process, which depend on the optical path length difference that can be resolved with a high precision of more than 16 standard deviations.

physics.optics↗

arXiv2024

Quantum Teleportation with Telecom Photons from Remote Quantum Emitters

The quest for a global quantum internet is based on the realization of a scalable network which requires quantum hardware with exceptional performance. Among them are quantum light sources providing deterministic, high brightness, high-fidelity entangled photons and quantum memories with coherence times in the millisecond range and above. To operate the network on a global scale, the quantum light source should emit at telecommunication wavelengths with minimum propagation losses. A cornerstone for the operation of such a quantum network is the demonstration of quantum teleportation. Here we realize full-photonic quantum teleportation employing one of the most promising platforms, i.e. semiconductor quantum dots, which can fulfill all the aforementioned requirements. Two remote quantum dots are used, one as a source of entangled photon pairs and the other as a single-photon source. The frequency mismatch between the triggered sources is erased using two polarization-preserving quantum frequency converters, enabling a Bell state measurement at telecommunication wavelengths. A post-selected teleportation fidelity of up to 0.721(33) is achieved, significantly above the classical limit, demonstrating successful quantum teleportation between light generated by distinct sources. These results mark a major advance for the semiconductor platform as a source of quantum light fulfilling a key requirement for a scalable quantum network. This becomes particularly relevant after the seminal breakthrough of addressing a nuclear spin in semiconductor quantum dots demonstrating long coherence times, thus fulfilling another crucial step towards a scalable quantum network.

quant-ph↗

arXiv2024

High fidelity distribution of triggered polarization-entangled telecom photons via a 36km intra-city fiber network

Fiber-based distribution of triggered, entangled, single-photon pairs is a key requirement for the future development of terrestrial quantum networks. In this context, semiconductor quantum dots (QDs) are promising candidates for deterministic sources of on-demand polarization-entangled photon pairs. So far, the best QD polarization-entangled-pair sources emit in the near-infrared wavelength regime, where the transmission distance in deployed fibers is limited. Here, to be compatible with existing fiber network infrastructures, bi-directional polarization-conserving quantum frequency conversion (QFC) is employed to convert the QD emission from \unit[780]{nm} to telecom wavelengths. We show the preservation of polarization entanglement after QFC (fidelity to Bell state $F_{ϕ^+, conv}=0.972\pm0.003$) of the biexciton transition. As a step towards real-world applicability, high entanglement fidelities ($F_{ϕ^+, loop}=0.945\pm0.005$) after the propagation of one photon of the entangled pair along a \unit[35.8]{km} field installed standard single mode fiber link are reported. Furthermore, we successfully demonstrate a second polarization-conversing QFC step back to \unit[780]{nm} preserving entanglement ($F_{ϕ^+, back}=0.903\pm0.005$). This further prepares the way for interfacing quantum light to various quantum memories.

quant-ph↗