Valentina Marulanda Acosta | LIP6 - Équipe QI

Multi-Actuator Lens Systems for Turbulence Correction in Free-Space Optical Communications

Mon, 01 Sep 2025 00:00:00 +0000

The implementation of efficient free-space channels is fundamental for both classical and quantum free-space optical (FSO) communication. This can be challenging for fiber-coupled receivers, due to the time variant inhomogeneity of the refractive index that can cause strong fluctuations in the power coupled into the single-mode fiber (SMF), and requires the use of adaptive optics (AO) systems to correct the atmospheric-induced aberrations. In this work, we present two adaptive optic systems, one using a fast-steering prism (FSP) for the correction of tip-tilt and a second one based on a multi-actuator deformable lens (MAL), capable of correcting up to the third order of Zernike’s polynomials. We test both systems at telecom wavelength both with artificial turbulence in the laboratory and on a free-space channel, demonstrating their effectiveness in increasing the fiber coupling efficiency.

Increasing the secret key rate of satellite-to-ground entanglement-based QKD assisted by adaptive optics

Tue, 26 Nov 2024 00:00:00 +0000

Future quantum networks will be composed of both terrestrial links for metropolitan and continent-scale connections and space-based links for global coverage and infrastructure resilience. However, the propagation of quantum signals through the atmosphere is severely impacted by the effects of turbulence. This is even more the case for entanglement-based quantum communication protocols requiring two free-space channels to be considered simultaneously. In this work, we assess the advantage of turbulence mitigation by adaptive optics, in particular during daytime link operation, so as to increase the coupling of the received signal into an optical fiber. We show in particular that this improves the performance of entanglement-based quantum key distribution by up to a few hundred bits per second when compared with the uncorrected scenario

QOSST : A Highly Modular Open Source Software for Continuous-Variable Quantum Key Distribution

Wed, 13 Nov 2024 00:00:00 +0000

Connecting Quantum Cities: Simulation of a Satellite-Based Quantum Network

Mon, 01 Jul 2024 00:00:00 +0000

We present and analyse an architecture for a European-scale quantum network using satellite links to connect Quantum Cities, which are metropolitan quantum networks with minimal hardware requirements for the end users. Using NetSquid, a quantum network simulation tool based on discrete events, we assess and benchmark the performance of such a network linking distant locations in Europe in terms of quantum key distribution rates, considering realistic parameters for currently available or near-term technology. Our results highlight the key parameters and the limits of current satellite quantum communication links and can be used to assist the design of future missions. We also discuss the possibility of using high-altitude balloons as an alternative to satellites.

QOSST: A Highly Modular Open Source Platform for Continuous Variable Quantum Key Distribution Applications

Sun, 23 Jun 2024 00:00:00 +0000

We present a highly modular Open Source Software to perform CV-QKD experiments. The software is hardware agnostic and was benchmarked on bulk and integrated receivers, reaching state of the art secret key rates.

QOSST: A Highly-Modular Open Source Platform for Experimental Continuous-Variable Quantum Key Distribution

Mon, 29 Apr 2024 00:00:00 +0000

Quantum Key Distribution (QKD) enables secret key exchange between two remote parties with information-theoretic security rooted in the laws of quantum physics. Encoding key information in continuous variables (CV), such as the values of quadrature components of coherent states of light, brings implementations much closer to standard optical communication systems, but this comes at the price of significant complexity in the digital signal processing techniques required for operation at low signal-to-noise ratios. In this work, we wish to lower the barriers to entry for CV-QKD experiments associated to this difficulty by providing a highly modular, open source software that is in principle hardware agnostic and can be used in multiple configurations. We benchmarked this software, called QOSST, using an experimental setup with a locally generated local oscillator, frequency multiplexed pilots and RF-heterodyne detection, and obtained state-of-the-art secret key rates of the order of Mbit/s over metropolitan distances at the asymptotic limit. We hope that QOSST can be used to stimulate further experimental advances in CV-QKD and be improved and extended by the community to achieve high performance in a wide variety of configurations.

Analysis of satellite-to-ground quantum key distribution with adaptive optics

Tue, 20 Feb 2024 00:00:00 +0000

Future quantum communication infrastructures will rely on both terrestrial and space-based links integrating high-performance optical systems engineered for this purpose. In space-based downlinks in particular, the loss budget and the variations in the signal propagation due to atmospheric turbulence effects impose a careful optimization of the coupling of light in single-mode fibers required for interfacing with the receiving stations and the ground networks. In this work, we perform a comprehensive study of the role of adaptive optics (AO) in this optimization, focusing on realistic baseline configurations of prepare-and-measure quantum key distribution (QKD), with both discrete and continuous-variable encoding, and including finite-size effects. Our analysis uses existing experimental turbulence datasets at both day and night time to model the coupled signal statistics following a wavefront distortion correction with AO, and allows us to estimate the secret key rate for a range of critical parameters, such as turbulence strength, satellite altitude and ground telescope diameter. The results we derive illustrate the interest of adopting advanced AO techniques in several practical configurations.

Quantum Key Distribution through atmospheric turbulence : secure satellite-to-ground links

Mon, 04 Dec 2023 00:00:00 +0000

The ever-growing demands of modern telecommunication systems in terms of data rates as well as the impending threat of the increasing computing power of modern computers, make the secure transmission of data an essential requirement and thus a very active field of study. Quantum key distribution (QKD) allows for the exchange of cryptographic keys whose security level does not depend on the complexity of a mathematical algorithm but rather relies on exploiting the properties of quantum mechanics cite{scarani2009}. Depending on the protocol, the key bits will be encoded either on the superposition of modes of individual photons, such as polarization modes, as is the case for the discrete variable protocols (DV) or they will be encoded into the quadratures of a very low flux electromagnetic field as it happens in the continuous variable protocols (CV). While offering security levels unattainable by classical means, QKD protocols in their terrestrial implementation are severely limited in distance reaching only several hundred kilometers because of the exponential attenuation suffered by fiber-transmitted signals. Since the amplification methods of classical optical communications repeaters are not compatible with a signal that is quantum in nature, and because of the current lack of technological maturity regarding quantum repeaters, satellite relays present an interesting alternative for the establishment of secure intercontinental quantum links. A study by Dequal et al. upon which a part of the present study is based on, examines the possibility of performing a continuous variable key exchange between a satellite and a ground station by proposing a modeling of the propagation channel accounting for the effects of beam wandering, a fluctuating atmospheric transmission and a fixed loss due to single mode fiber coupling. It is as an in-depth continuation of this analysis that this simulation study was initially developed. Taking into account in particular the effects of propagation through the turbulent atmosphere on the spatial coherence of the optical signal, as well as expanding on the protocols taken into account. Adaptive optics (AO) are able to partially correct some of the aforementioned propagation effects. A typical AO system consists of a feedback loop containing elements capable of measuring and correcting wavefront aberrations in real time and we will focus our efforts in analyzing the effect of such a system in the performance of several protocols of quantum key distribution under different scenarios.

Quantum Key Distribution through atmospheric turbulence: secure satellite-to-ground links

Mon, 04 Dec 2023 00:00:00 +0000

Les exigences sans cesse croissantes des systèmes de télécommunication modernes font de la transmission sécurisée des données à la fois une exigence essentielle et un défi majeur, et donc un domaine d’étude très actif. La distribution de clés quantiques (QKD) permet l’échange de clés cryptographiques dont le niveau de sécurité est intrinsèquement basé sur l’exploitation des propriétés de la mécanique quantique. Cependant, le déploiement de systèmes QKD via des réseaux de fibres terrestres est très limité en distance à cause de l’atténuation, et comme les méthodes d’amplification conventionnelles ne sont pas compatibles avec un signal quantique, les relais satellitaires se présentent comme une alternative prometteuse pour établir des liaisons quantiques intercontinentales sécurisées.

Nous présentons un modèle complet du canal atmosphérique dans le contexte d’un lien QKD descendant entre un satellite en orbite basse et le sol. Ce modèle tient compte de la turbulence, de sa correction partielle par l’optique adaptative (AO), des pertes géométriques et des fluctuations de pointage du satellite. Nous utilisons ce modèle pour évaluer les performances de trois protocoles QKD, pour différents paramètres du système et en tenant compte des effets de taille finie. Les résultats montrent les avantages de l’utilisation d’un système d’OA, la performance en termes de taux de clé de tous les protocoles analysés s’améliore lorsqu’on considère une correction d’OA. Pour valider nos résultats de simulation, nous avons également commencé à mettre en œuvre un banc d’essai expérimental basé sur une émulation simplifiée du canal atmosphérique et un système CV-QKD.

Experimental Demonstration of Continuous-Variable Quantum Key Distribution with a Photonic Integrated Receiver and Modular Software

Wed, 22 Nov 2023 00:00:00 +0000

Improvement of satellite-to-ground QKD secret key rate with adaptive optics

Sun, 05 Mar 2023 00:00:00 +0000

We demonstrate the gain brought by adaptive optics for space-ground QKD links. Refined modeling of turbulence, adaptive optics and QKD, including finite-size effects, shows improvement by several orders of magnitude of the secret key rate.

Satellite-to-ground quantum key distribution with adaptive optics

Fri, 28 Jan 2022 16:00:00 +0200

Future quantum communication infrastructures will rely on both terrestrial and space-based links integrating high-performance optical systems engineered for this purpose. In space-based downlinks in particular, the loss budget and the variations in the signal propagation due to atmospheric turbulence effects impose a careful optimization of the coupling of light in single-mode fibers required for interfacing with the receiving stations and the ground networks. In this work, through a variety of simulations we model the effects of turbulence on the transmission of the signal, its partial correction via an adaptive optics (AO) system and finally we compute the corresponding secret key rate for both continuous-variable (CV) and discrete variable (DV) quantum key distribution protocols. Our analysis allows us to estimate the key rate for a range of critical parameters, such as turbulence strength, satellite altitude and ground telescope diameter. The results we derive illustrate the interest of adopting advanced AO techniques in several practical configurations.