arXiv subjects

Ilektra Karakosta-Amarantidou

Publications and source records attributed to Ilektra Karakosta-Amarantidou.

5 recordsLinked to original sources

arXiv2026

Intermodal quantum key distribution over an 18 km free-space channel with adaptive optics and room-temperature detectors

Intermodal quantum key distribution at telecom wavelengths provides a hybrid interface between fiber connections and free-space links, both essential for the realization of scalable and interoperable quantum networks. Although demonstrated over short-range free-space links, long-distance implementations of intermodal quantum key distribution remain challenging, due to turbulence-induced wavefront aberrations which limit efficient single-mode fiber coupling at the optical receiver. Here, we demonstrate a real-time intermodal quantum key distribution field trial over an 18 km free-space link, connecting a remote terminal to an urban optical ground station equipped with a 40 cm-class telescope. An adaptive optics system, implementing direct wavefront sensing and high-order aberration correction, enables efficient single-mode fiber coupling and allows secure key generation of 200 bit/s using a compact state analyzer equipped with room-temperature detectors. We further validate through experimental data a turbulence-based model for predicting fiber coupling efficiency, providing practical design guidelines for future intermodal quantum networks.

quant-ph↗

arXiv2026

GHz-rate polarization-based QKD system for fiber and satellite applications

Quantum key distribution (QKD) leverages the principles of quantum mechanics to exchange a secret key between two parties. Despite its promising features, QKD also faces several practical challenges such as transmission loss, noise in quantum channels and finite key size effects. Addressing these issues is crucial for the large-scale deployment of QKD in fiber and satellite networks. In this paper, we present a 1550 nm QKD system realizing the efficient-BB84 protocol and based on the iPOGNAC scheme. The system achieved repetition rates up to 1.5~GHz and showed an intrinsic QBER of $\sim 0.4\%$. The system was first tested on a laboratory fiber link and then on an intermodal link in the field, consisting of both deployed fiber and a 620 m free-space channel. The experiment was performed in daylight conditions, exploiting the Qubit4Sync synchronization protocol. With this trial, we achieved a new benchmark for free-space BB84 QKD systems by generating a sustained secret key rate (SKR) above 1~Mb/s for 1 hour. Finally, exploiting a recently discovered finite-size bound, we achieved a secure key rate of about 10 Mb/s at low losses (5 dB), and around 6.5~kb/s in the high-loss (38.5 dB), low block length ($N=10^4$) regime. The latter results demonstrate the system's suitability for highly lossy and time-constrained scenarios such as QKD from low Earth orbit satellites.

quant-ph↗

arXiv2025

Intermodal quantum key distribution field trial with active switching between fiber and free-space channels

Intermodal quantum key distribution enables the full interoperability of fiber networks and free-space channels, which are both necessary elements for the development of a global quantum network. We present a field trial of an intermodal quantum key distribution system in a simple 3-node heterogeneous quantum network - comprised of two polarization-based transmitters and a single receiver - in which the active channel is alternately switched between a free-space link of 620 m and a 17km-long deployed fiber in the metropolitan area of Padova. The performance of the free-space channel is evaluated against the atmospheric turbulence strength of the link. The field trial lasted for several hours in daylight conditions, attesting the interoperability between fiber and free-space channels, with a secret key rate of the order of kbps for both the channels. The QKD hardware and software require no different strategies to work over the two channels, even if the intrinsic characteristics of the links are clearly different. The switching system represents a cost-effective solution for a trusted quantum key distribution network, reducing the number of necessary devices in different network topologies.

quant-ph↗

arXiv2024

Free-space model for a balloon-based quantum network

Long-distance communication is one of the main bottlenecks in the development of quantum communication networks. Free-space communication is a way to circumvent exponential fiber loss and to allow longer communication distances. Satellite nodes are the main devices currently studied for free-space communication, but they come with downsides such as high cost and low availability. In this work, we study an alternative to satellites, namely aerial platforms such as high-altitude balloons. We provide a loss model to simulate the channel efficiency of balloon-to-ground, ground-to-balloon, and balloon-to-balloon communication channels, considering a large set of hardware parameters. We perform a parameter exploration to exhibit important trade-offs in these channels, as well as simulations of different quantum key distribution network architectures including balloon nodes. We demonstrate that balloons are a realistic alternative to satellites for free-space communications in national network architectures.

quant-ph↗

arXiv2023

The Evolution from Design to Verification of the Antenna System and Mechanisms in the AcubeSAT mission

AcubeSAT is an open-source CubeSat mission aiming to explore the effects of microgravity and radiation on eukaryotic cells using a compact microfluidic LoC platform. It is developed by SpaceDot, a volunteer, interdisciplinary student team at the Aristotle University of Thessaloniki and supported by the "Fly Your Satellite! 3" program of the ESA Education Office. The scientific data of the mission is comprised of microscope images captured through the on-board integrated camera setup. As the total size of the payload data is expected to be close to 2GB over 12 months, a fast and efficient downlink fulfilling the restrictive power, cost and complexity budgets is required. Currently, there is no open-source communications system design which fully supports these specific constraints, so we opted to develop our own solutions. The antenna system underwent multiple iterations as the design matured, a process highly aided by the feedback received from the ESA experts. The final communications system configuration consists of an S-band microstrip antenna operating at 2.4GHz and a UHF deployable antenna, for the payload data and TM&TC respectively, both in-house designed. In this paper, we will present AcubeSAT's antenna system iterations that span over 3 years, as well as the rationale and analysis results behind each. The development decisions will be highlighted throughout the paper in an effort to aid in the future development of such a low-cost CubeSat mission communications system.

eess.SY↗