arXiv subjects

Asli Cakan

Publications and source records attributed to Asli Cakan.

5 recordsLinked to original sources

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↗

arXiv2025

Raman Signatures of Single Point Defects in Hexagonal Boron Nitride Quantum Emitters

Point defects in solid-state quantum systems are vital for enabling single-photon emission at specific wavelengths, making their precise identification essential for advancing applications in quantum technologies. However, pinpointing the microscopic origins of these defects remains a challenge. In this work, we propose Raman spectroscopy as a robust strategy for defect identification. Using density functional theory, we systematically characterize the Raman signatures of 100 defects in hexagonal boron nitride (hBN) spanning periodic groups III to VI, encompassing around 30,000 phonon modes. Our findings reveal that the local atomic environment plays a pivotal role in shaping the Raman lineshape, enabling the narrowing of potential defect candidates. Furthermore, we demonstrate that Raman spectroscopy can differentiate defects based on their spin and charge states as well as strain-induced variations, implying the versatility of this approach. Therefore, this study not only provides a comprehensive theoretical database of Raman spectra for hBN defects but also establishes a novel experiment framework for using tip-enhanced Raman spectroscopy to identify point defects. More broadly, our approach offers a universal method for defect identification in any quantum materials.

cond-mat.mtrl-sci↗

arXiv2024

The hBN defects database: a theoretical compilation of color centers in hexagonal boron nitride

Color centers in hexagonal boron nitride (hBN) have become an intensively researched system due to their potential applications in quantum technologies. There has been a large variety of defects being fabricated, yet, for many of them, the atomic origin remains unclear. The direct imaging of the defect is technically very challenging, in particular since, in a diffraction-limited spot, there are many defects and then one has to identify the one that is optically active. Another approach is to compare the photophysical properties with theoretical simulations and identify which defect has a matching signature. It has been shown that a single property for this is insufficient and causes misassignments. Here, we publish a density functional theory (DFT)-based searchable online database covering the electronic structure of hBN defects (257 triplet and 211 singlet configurations), as well as their photophysical fingerprint (excited state lifetime, quantum efficiency, transition dipole moment and orientation, polarization visibility, and many more). All data is open-source and publicly accessible at https://h-bn.info and can be downloaded. It is possible to enter the experimentally observed defect signature and the database will output possible candidates which can be narrowed down by entering as many observed properties as possible. The database will be continuously updated with more defects and new photophysical properties (which can also be specifically requested by any users). The database therefore allows one to reliably identify defects but also investigate which defects might be promising for magnetic field sensing or quantum memory applications.

quant-ph↗

arXiv2024

Comparative study of quantum emitter fabrication in wide bandgap materials using localized electron irradiation

Quantum light sources are crucial foundational components for various quantum technology applications. With the rapid development of quantum technology, there has been a growing demand for materials with the capability of hosting quantum emitters. One such material platform uses fluorescent defects in hexagonal boron nitride (hBN) that can host deep sublevels within the bandgap. The localized electron irradiation has shown its effectiveness in generating deep sublevels to induce single emitters in hBN. The question is whether localized (electron beam) irradiation is a reliable tool for creating emitters in other wide bandgap materials and its uniqueness to hBN. Here, we investigate and compare the fabrication of quantum emitters in hBN and exfoliated muscovite mica flakes along with other 3D crystals, such as silicon carbide and gallium nitride, which are known to host quantum emitters. We used our primary fabrication technique of localized electron irradiation using a standard scanning electron microscope. To complement our experimental work, we employed density functional theory simulations to study the atomic structures of defects in mica. While our fabrication technique allows one to create hBN quantum emitters with a high yield and high single photon purity, it is unable to fabricate single emitters in the other solid-state crystals under investigation. This allows us to draw conclusions on the emitter fabrication mechanism in hBN, which could rely on activating pre-existing defects by charge state manipulation. Therefore, we provide an essential step toward the identification of hBN emitters and their formation process.

physics.app-ph↗

arXiv2024

Identifying electronic transitions of defects in hexagonal boron nitride for quantum memories

A quantum memory is a crucial keystone for enabling large-scale quantum networks. Applicable to the practical implementation, specific properties, i.e., long storage time, selective efficient coupling with other systems, and a high memory efficiency are desirable. Though many quantum memory systems are developed thus far, none of them can perfectly meet all requirements. This work herein proposes a quantum memory based on color centers in hexagonal boron nitride (hBN), where its performance is evaluated based on a simple theoretical model of suitable defects in a cavity. Employing density functional theory calculations, 257 triplet and 211 singlet spin electronic transitions are investigated. Among these defects, it is found that some defects inherit the $Λ$ electronic structures desirable for a Raman-type quantum memory and optical transitions can couple with other quantum systems. Further, the required quality factor and bandwidth are examined for each defect to achieve a 95% writing efficiency. Both parameters are influenced by the radiative transition rate in the defect state. In addition, inheriting triplet-singlet spin multiplicity indicates the possibility of being a quantum sensing, in particular, optically detected magnetic resonance. This work therefore demonstrates the potential usage of hBN defects as a quantum memory in future quantum networks.

quant-ph↗