arXiv subjects

Olivier Alibart

Publications and source records attributed to Olivier Alibart.

At least 19 recordsLinked to original sources

arXiv2026

Dual wavelength source of entanglement for space quantum communication

We report the demonstration of a bulk, intrinsically phase-stable source of polarization- and time-energy-entangled photon pairs at 810nm and 1550nm, directly coupled into single-mode optical fibers. This highly non-degenerate wavelength combination is well suited for hybrid quantum communication networks, enabling low-loss transmission in optical fibers at 1550nm while maintaining efficient free-space propagation and detection at 810nm. The source is based on spontaneous parametric down-conversion in a periodically poled lithium niobate crystal embedded in a polarization Sagnac interferometer, providing inherent stability and dual-degree-of-freedom entanglement. We measure a spectral brightness of B = 4800 pair/s/mW/GHz, with fiber coupling efficiencies exceeding 0.48 at both wavelengths. The entanglement quality is characterized by high-visibility two-photon interference, yielding net visibilities of 0.995 in the polarization basis and 0.991 in the energy-time basis. These performances demonstrate a compact and robust entanglement source compatible with hybrid fiber/free-space quantum key distribution architectures, and suitable for future ground-to-satellite quantum communication links.

quant-ph↗

arXiv2026

NovaMoon: A Strategic Lunar Reference Station for Positioning, Timing, and Largely Enhanced Science in the Earth-Moon System

The renewed interest in lunar exploration and the development of future lunar communication and navigation services highlight the need for a precise, stable, and interoperable geodetic and timing infrastructure on the Moon. NovaMoon, proposed as a scientific and navigation payload for ESA's Argonaut lander, is designed as a lunar-based local differential, geodetic, and timing station supporting both operational needs in the Moon's south polar region and a broad range of scientific investigations. The payload integrates a lunar laser retroreflector, a Very Long Baseline Interferometry transmitter, a receiver for navigation signals compatible with LunaNet standards, high-stability atomic clocks, and direct-to-Earth radio links -- making it the first lunar station to co-locate multiple ranging, tracking, and timing techniques. NovaMoon will enable sub-metre to decimetre positioning, provide local differential corrections for lunar users, and ensure an accurate and stable realisation of position and time. Preliminary simulation studies show that this multi-technique dataset improves the lunar reference frame, orientation and ephemerides, and estimates of interior parameters like tidal response and core properties. NovaMoon will also provide the first long-duration physical realisation of a lunar time reference. Beyond its primary goals, it supports improved cartography, precise surface geolocation, and higher-resolution topography, contributing to safer landings and operations. It also enables new tests of fundamental physics, including constraints on relativity and possible deviations from classical gravity.

astro-ph.EP↗

arXiv2026

High-brightness fiber-based Sagnac source of entangled photon pairs for multiplexed quantum networks

A fully fibered source of entangled photon pairs based on a nonlinear Sagnac interferometer is reported. Operating at telecom wavelengths, the source relies exclusively on standard fiber-optic components and periodically poled lithium niobate (PPLN) waveguides, resulting in a compact, robust, and field-deployable architecture. The generation stage supports both polarization and energy-time entanglement without modification, enabling versatile operation depending on the targeted application. Broadband spontaneous parametric down-conversion allows dense wavelength-division multiplexing over the telecom C and L bands. High normalized brightness (10.3 kpairs/s/nm/mW$^2$) is achieved on a standard 100 GHz ITU channel pair, together with high entanglement quality. Polarization and energy-time encodings are characterized through state tomography and two-photon interference measurements, yielding fidelities, purities, and visibilities exceeding 96 % over multiple wavelength channels. The stability and reproducibility of the source are further evaluated through long-duration operation in a network environment. These results demonstrate that the proposed Sagnac source constitutes a practical and scalable building block for future plug-and-play quantum communication and quantum networking platforms.

quant-ph↗

arXiv2025

Deployed quantum key distribution network: further, longer and more users

Entanglement-based quantum links are the backbone of future quantum internet networks, enabling secure communication between distant cities. Realizing such networks requires addressing multiple practical challenges in long-distance quantum key distribution : time synchronisation, interferometer stabilisation and automation. Here, we report several advances. First, we maintained an operational QKD link continuously for 325hours over 50km between two remotes locations, demonstrating the feasibility of long-duration key generation. We further extended secure key distribution up to a 100km operational link connecting the University of Nice to a ground-based optical station, a setup compatible with future quantum satellite connections. Finally, by employing wavelength demultiplexing to separate photons of entangled pairs, we performed QKD across multiple ITU channels, achieving secure key exchange via the BBM92 protocol and time-energy observables.

quant-ph↗

arXiv2025

An ETSI GS QKD compliant TLS implementation

A modification of the TLS protocol is presented, using our implementation of the Quantum Key Distribution (QKD) standard ETSI GS QKD 014 v1.1.1. We rely on the Rustls library for this. The TLS protocol is modified while maintaining backward compatibility on the client and server side. We thus wish to participate in the effort to generalize the use of QKD on the Internet. We used our protocol for a video conference call encrypted by QKD. Finally, we analyze the performance of our protocol, comparing the time needed to establish a handshake to that of TLS 1.3.

cs.CR↗

arXiv2025

MULTISS: un protocole de stockage confidentiel {à} long terme sur plusieurs r{é}seaux QKD

This paper presents MULTISS, a new protocol for long-term storage distributed across multiple Quantum Key Distribution (QKD) networks. This protocol is an extension of LINCOS, a secure storage protocol that uses Shamir secret sharing for secret storage on a single QKD network. Our protocol uses hierarchical secret sharing to distribute a secret across multiple QKD networks while ensuring perfect security. Our protocol further allows for sharing updates without having to reconstruct the entire secret. We also prove that MULTISS is strictly more secure than LINCOS, which remains vulnerable when its QKD network is compromised.

cs.CR↗

arXiv2025

An all-fibred, telecom technology compatible, room temperature, single-photon source

Single photon sources are essential building blocks for fundamental quantum optics but also for quantum information networks. Their widespread is currently hindered by unpractical features, such as operation at cryogenic temperature and emission wavelength lying outside telecom windows. Taking advantage of telecom technology and point defects in GaN crystals, we present, for the first time, the development of a fully-fibred source of single photons operating at room temperature, emitting photons in the telecom O-band and fulfilling the standards of telecom photonics. We characterise an emitter producting single photons at the wavelength of 1292\,nm, a spectral broadening compatible with CWDM channels of 13\,nm, and a brightness of 25 kcps per mW of pump power. The source shows a signal-to-noise ratio of 16.5 and an autocorrelation degree (purity) of 0,059 at room temperature, showing high potential for being integrated transportable quantum cryptography devices.

quant-ph↗

arXiv2025

Entanglement-based clock syntonization for quantum key distribution networks. Demonstration over a 50 km-long link

We present the implementation of a time synchronization protocol as part of an experimentally deployed entanglement-based quantum key distribution (QKD) link. The system is deployed over 48 km of optical fibers across the Métropole Côte d'Azur and enables secret cryptographic key exchange between two remote users, with an average rate of 7 kbps. We exploit the time correlation of paired photons generated by a high-quality source of energy-time entanglement implemented in the QKD link to synchronize two rubidium clocks located at the end stations. The level of stability achieved guarantees a time offset between the clocks under 12 ps at all time. We also show that this protocol requires less hardware than a typical synchronization protocol for QKD that would distribute a reference clock signal between the users.

quant-ph↗

arXiv2023

Satellite-based Quantum Information Networks: Use cases, Architecture, and Roadmap

Quantum Information Networks (QINs) attract increasing interest, as they enable connecting quantum devices over long distances, thus greatly enhancing their intrinsic computing, sensing, and security capabilities. The core mechanism of a QIN is quantum state teleportation, consuming quantum entanglement, which can be seen in this context as a new kind of network resource. Here we identify use cases per activity sector, including key performance targets, as a reference for the network requirements. We then define a high-level architecture of a generic QIN, before focusing on the architecture of the Space segment, with the aim of identifying the main design drivers and critical elements. A survey of the state-of-the-art of these critical elements is presented, as are issues related to standardisation. Finally, we explain our roadmap to developing the first QINs and detail the already concluded first step, the design and numerical simulation of a Space-to-ground entanglement distribution demonstrator.

quant-ph↗

arXiv2022

Operational entanglement-based quantum key distribution over 50 km of real-field optical fibres

We present a real field quantum key distribution link based on energy-time entanglement. Three nodes are connected over the city of Nice by means of optical fibers with a total distance of 50\,km. We have implemented a high-quality source of energy-time entangled photon pairs and actively stabilized analysers to project the quantum states, associated with an innovative remote synchronization method of the end stations' clocks which does not require any dedicated channel. The system is compatible with the ITU 100\,GHz standard telecom-grid, through which a raw key rate of 40\,kbps per pair of channels is obtained. A post-treatment software performs all the necessary post-processing procedures enabling to establish secret keys in real time. All of those embedded systems and achieved performance make this network the first fully operational entanglement based metropolitan quantum network to be implemented in real field.

quant-ph↗

arXiv2020

Configurable heralded two-photon Fock-states on a chip

Progress in integrated photonics enables combining several elementary functions on single substrates for realizing advanced functionnalized chips. We report a monolithic integrated quantum photonic realization on lithium niobate, where nonlinear optics and electro-optics properties have been harnessed simultaneously for generating heralded configurable, two-photon states. Taking advantage of a picosecond pump laser and telecom components, we demonstrate the production of various path-coded heralded two-photon states, showing 94\% raw visibility for Hong-Ou-Mandel interference. The versatility and performance of such a highly integrated photonic entanglement source enable exploring more complex quantum information processing protocols finding application in communication, metrology and processing tasks.

quant-ph↗

arXiv2020

Two-photon phase-sensing with single-photon detection

Path-entangled multi-photon states allow optical phase-sensing beyond the shot-noise limit, provided that an efficient parity measurement can be implemented. Realising this experimentally is technologically demanding, as it requires coincident single-photon detection proportional to the number of photons involved, which represents a severe challenge for achieving a practical quantum advantage over classical methods. Here, we exploit advanced quantum state engineering based on superposing two photon-pair creation events to realise a new approach that bypasses this issue. In particular, optical phase shifts are probed with a two-photon quantum state whose information is subsequently effectively transferred to a single-photon state. Notably, without any multiphoton detection, we infer phase shifts by measuring the average intensity of the single-photon beam on a photodiode, in analogy to standard classical measurements. Importantly, our approach maintains the quantum advantage: twice as many interference fringes are observed for the same phase shift, corresponding to N=2 path-entangled photons. Our results demonstrate that the advantages of quantum-enhanced phase-sensing can be fully exploited in standard intensity measurements, paving the way towards resource-efficient and practical quantum optical metrology.

quant-ph↗

arXiv2020

A universal, plug-and-play synchronisation scheme for practical quantum networks

We propose and experimentally demonstrate a plug-and-play, practical, and enabling method allowing to synchronize the building blocks of a quantum network in an all-optical way. Our scheme relies on mature and reliable classical telecommunication and non-linear optical technologies and can be implemented in a universal way with off-the-shelf components. Compared to already reported solutions, it allows achieving high-quality synchronization compatible with high network-operation rate and is free from opto-electronic jitters affecting servo-loop based configurations. We test our scheme with a genuine quantum optical method in terms of the interference between two photons coming from two remotely synchronized sources spaced by distances of up to 100 km. Measured visibilities well above 90% confirm the validity of our approach. Due its simplicity and high-quality performance, our scheme paves the way for the synchronization of long-distance quantum networks based on fibre, free-space, as well as hybrid solutions.

quant-ph↗

arXiv2020

High-quality photonic entanglement based on a silicon chip

The fruitful association of quantum and integrated photonics holds the promise to produce, manipulate, and detect quantum states of light using compact and scalable systems. Integrating all the building-blocks necessary to produce high-quality photonic entanglement in the telecom wavelength range out of a single chip remains a major challenge, mainly due to the limited performance of on-chip light rejection filters. We report a stand-alone, telecom-compliant, device that integrates, on a single substrate, a nonlinear photon-pair generator and a passive pump rejection filter. Using standard channel-grid fiber demultiplexers, we demonstrate the first entanglement quantification of such a integrated circuit, showing the highest raw quantum interference visibility for energy-time entangled photons over two telecom-wavelength bands. Genuinely pure maximally entangled states can therefore be generated thanks to the high-level of noise suppression obtained with the pump filter. These results will certainly further promote the development of more advanced and scalable photonic-integrated quantum systems compliant with telecommunication standards.

quant-ph↗

arXiv2019

Fibre based hyperentanglement generation for dense wavelength division multiplexing

Entanglement is a key resource in quantum information science and associated emerging technologies. Photonic systems offer a large range of exploitable entanglement degrees of freedom such as frequency, time, polarization, and spatial modes. Hyperentangled photons exploit multiple degrees of freedom simultaneously to enhance the performance of quantum information protocols. Here, we report a fully guided-wave approach for generating polarization and energy-time hyperentangled photons at telecom wavelengths. Moreover, by demultiplexing the broadband emission spectrum of the source into five standard telecom channel pairs, we demonstrate compliance with fibre network standards and improve the effective bit rate capacity of the quantum channel up to one order of magnitude. In all channel pairs, we observe a violation of a generalised Bell inequality by more than 27 standard deviations, underlining the relevance of our approach.

quant-ph↗

arXiv2019

Quantum optical frequency up-conversion for polarisation entangled qubits: towards interconnected quantum information devices

Realising a global quantum network requires combining individual strengths of different quantum systems to perform universal tasks, notably using flying and stationary qubits. However, transferring coherently quantum information between different systems is challenging as they usually feature different properties, notably in terms of operation wavelength and wavepacket. To circumvent this problem for quantum photonics systems, we demonstrate a polarisation-preserving quantum frequency conversion device in which telecom wavelength photons are converted to the near infrared, at which a variety of quantum memories operate. Our device is essentially free of noise which we demonstrate through near perfect single photon state transfer tomography and observation of high-fidelity entanglement after conversion. In addition, our guided-wave setup is robust, compact, and easily adaptable to other wavelengths. This approach therefore represents a major building block towards advantageously connecting quantum information systems based on light and matter.

quant-ph↗

arXiv2018

Broadband integrated beam splitter using spatial adiabatic passage

Light routing and manipulation are important aspects of integrated optics. They essentially rely on beam splitters which are at the heart of interferometric setups and active routing. The most common implementations of beam splitters suffer either from strong dispersive response (directional couplers) or tight fabrication tolerances (multimode interference couplers). In this paper we fabricate a robust and simple broadband integrated beam splitter based on lithium niobate with a splitting ratio achromatic over more than 130 nm. Our architecture is based on spatial adiabatic passage, a technique originally used to transfer entirely an optical beam from a waveguide to another one that has been shown to be remarkably robust against fabrication imperfections and wavelength dispersion. Our device shows a splitting ratio of 0.52$\pm $0.03 and 0.48$\pm $0.03 from 1500\,nm up to 1630\,nm. Furthermore, we show that suitable design enables the splitting in output beams with relative phase 0 or $π$. Thanks to their independence to material dispersion, these devices represent simple, elementary components to create achromatic and versatile photonic circuits.

quant-ph↗

arXiv2016

On-chip generation of heralded photon-number states

Beyond the use of genuine monolithic integrated optical platforms, we report here a hybrid strategy enabling on-chip generation of configurable heralded two-photon states. More specifically, we combine two different fabrication techniques, \textit{i.e.}, non-linear waveguides on lithium niobate for efficient photon-pair generation and femtosecond-laser-direct-written waveguides on glass for photon manipulation. Through real-time device manipulation capabilities, a variety of path-coded heralded two-photon states can be produced, ranging from product to entangled states. Those states are engineered with high levels of purity, assessed by fidelities of 99.5$\pm$8\% and 95.0$\pm$8\%, respectively, obtained via quantum interferometric measurements. Our strategy therefore stands as a milestone for further exploiting entanglement-based protocols, relying on engineered quantum states, and enabled by scalable and compatible photonic circuits.

quant-ph↗