arXiv subjects

Julien Chénedé

Publications and source records attributed to Julien Chénedé.

4 recordsLinked to original sources

arXiv2026

A proposal for a hybrid free-space optical quantum communication network with hexagonal boron nitride-based single photon sources

Hexagonal boron nitride (hBN) is known as a promising solid-state platform to host room temperature quantum emitters that produce high purity single photons. The bright and spectrally adaptable hBN emitters are space-compatible, making hBN well-suited for satellite-based free-space optical (FSO) quantum key distribution (QKD) at wavelengths where the atmospheric background is naturally suppressed. This paper presents a pathway to develop hBN emitters operating near the Ca-II Fraunhofer line (at 854 nm), enabling daylight FSO operation. Moreover, due to its compatibility with the first telecommunication window at 850 nm, it is possible to interface with optical fibers to bridge the `last mile' in a scenario where multiple end-users connect through a single optical ground station to a QKD satellite. We therefore introduce a concept that combines continuous operation of a quantum network, hybrid links to minimize deployment costs, and high data rates due to the use of realistic single photon sources. The realization would be an important milestone for the development of the quantum internet.

quant-ph↗

arXiv2026

Insights into the Nature of Quantum Emitters in Electron-Irradiated hexagonal Boron Nitride

Quantum emitters in hexagonal boron nitride (hBN) have emerged as a promising solid-state platform for quantum technology applications. However, a persistent challenge in the field is the unclear origin of many observed emission lines, particularly in the visible range, which can be difficult to distinguish from signals arising from organic or process-induced contamination during sample preparations and handling. This ambiguity limits both the reproducibility of emitter generation and the reliable identification of truly intrinsic quantum defects. This work provides a step-by-step framework to assess whether quantum emitters in electron-irradiated hBN are associated with organic contaminants introduced during sample preparation. We employ hyperspectral imaging, thermal annealing, and oxygen plasma etching to investigate the origin of the green-yellow emitters in electron-irradiated hBN. The combined results not only rule out organic contamination as the source of emission but also provide insight into the spectral variability, thermal stability, and vertical localization of the emitters generated in electron-irradiated hBN that was created without any pre- or post-processing. In addition, our experiments demonstrate the feasibility of creating stable emitters in hBN with thicknesses below 10 nm. These findings provide practical guidance for the identification and controlled implementation of hBN-based single-photon emitters in quantum photonic devices.

physics.optics↗

arXiv2026

Broadband Polarization Compensation with Link Segment Reconstruction for Quantum Optical Links

Polarization-encoded quantum communication requires compensation of polarization transformations induced by the optical links. If the compensator is embedded between two channel segments, the transformations before and after the compensator must be treated separately. Moreover, standard three-wave-plate polarization controllers can become non-universal when their retardances deviate from their ideal values. To address these two challenges, we introduce a four-wave plate compensator that synthesizes arbitrary SO(3) polarization transformations over a broad wavelength range, and an eight-Stokes vector protocol that reconstructs the two link-segment Mueller matrices on either side of the compensator. Our experiment reveals that the four-plate sequence suppresses polarization-induced excess quantum bit error rate (QBER) to the sub-percent level at an operating wavelength more than 100 nm from the design wavelength without further optimization. Combined with two auxiliary wavelengths, our scheme tracks the temperature-driven drift of a strongly wavelength-sensitive fiber spool while keeping the excess QBER below 1%. These results support flexible compensator placement and wavelength channel selection, as well as non-interruptive polarization control in wavelength-division-multiplexed quantum optical links.

quant-ph↗

arXiv2026

QuaNTUM: A Modular Quantum Communication Testbed for Scalable Fiber and Satellite Integration

Secure communication is essential for modern society, from financial transactions to critical infrastructure. As classical encryption faces threats from advancing computational power, quantum communication provides a fundamentally secure alternative based on physical laws. We present QuaNTUM (Quantum Network at the Technical University of Munich), a modular and extensible quantum communication testbed enabling scalable experiments across fiber-based campus networks and satellite-ground links. The terrestrial network connects research institutions in Garching near Munich via single-mode fibers in a star topology with polarization-maintaining components, multiplexers, and time-synchronized analysis modules. Active polarization control and real-time feedback support stable qubit transmission for high-fidelity quantum key distribution and entanglement distribution. A key feature is the integration of deterministic solid-state single-photon sources, including defects in hexagonal boron nitride and excited erbium atoms, with initial deployments on small satellites to bridge terrestrial and free-space channels. As an open-access platform, QuaNTUM enables protocol development, device benchmarking, and hybrid network research, providing a foundation for scalable quantum communication and future global quantum networks.

quant-ph↗