Simon Neves | LIP6 - Équipe QI

Experimentally Certified Transmission of a Quantum Message through an Untrusted and Lossy Quantum Channel via Bell's Theorem

Wed, 01 Jan 2025 00:00:00 +0000

Quantum transmission links are central elements in essentially all protocols involving the exchange of quantum messages. Emerging progress in quantum technologies involving such links needs to be accompanied by appropriate certification tools. In adversarial scenarios, a certification method can be vulnerable to attacks if too much trust is placed on the underlying system. Here, we propose a protocol in a device-independent framework, which allows for the certification of practical quantum transmission links in scenarios in which minimal assumptions are made about the functioning of the certification setup. In particular, we take unavoidable transmission losses into account by modeling the link as a completely positive trace-decreasing map. We also, crucially, remove the assumption of independent identically distributed samples, which is known to be incompatible with adversarial settings. Particular emphasis is put on a one-sided device-independent scenario, in which the sender possesses trusted resources. Finally, in view of the use of the certified transmitted states for follow-up applications, our protocol moves beyond certification of the channel to allow us to estimate the quality of the transmitted quantum message itself. To illustrate the practical relevance and the feasibility of our protocol with currently available technology, we provide an experimental implementation in the one-sided device-independent setting, based on a state-of-the-art polarization-entangled photon-pair source in a Sagnac configuration, and analyze its robustness for realistic losses and errors.

Realizing a Compact, High-Fidelity, Telecom-Wavelength Source of Multipartite Entangled Photons

Mon, 25 Nov 2024 00:00:00 +0000

Multipartite entangled states are an essential building block for advanced quantum networking applications. Realizing such tasks in practice puts stringent requirements on the characteristics of the states in terms of fidelity and generation rate, along with a desired compatibility with telecommunication network deployment. Here, we demonstrate a photonic platform design capable of producing high-fidelity Greenberger-Horne-Zeilinger (GHZ) states, at telecom wavelength and in a compact and scalable configuration. Our source relies on spontaneous parametric down-conversion in a layered Sagnac interferometer, which only requires a single nonlinear crystal. This enables the generation of highly indistinguishable photon pairs, leading by entanglement fusion to four-qubit polarization-entangled GHZ states with fidelity up to $(94.73 \pm 0.21)%$ with respect to the ideal state, at a rate of 1.7Hz. We provide a complete characterization of our source and highlight its suitability for practical quantum network applications.

Experimental cheat-sensitive quantum weak coin flipping

Fri, 01 Dec 2023 00:00:00 +0000

As in modern communication networks, the security of quantum networks will rely on complex cryptographic tasks that are based on a handful of fundamental primitives. Weak coin flipping (WCF) is a significant such primitive which allows two mistrustful parties to agree on a random bit while they favor opposite outcomes. Remarkably, perfect information-theoretic security can be achieved in principle for quantum WCF. Here, we overcome conceptual and practical issues that have prevented the experimental demonstration of this primitive to date, and demonstrate how quantum resources can provide cheat sensitivity, whereby each party can detect a cheating opponent, and an honest party is never sanctioned. Such a property is not known to be classically achievable with information-theoretic security. Our experiment implements a refined, loss-tolerant version of a recently proposed theoretical protocol and exploits heralded single photons generated by spontaneous parametric down conversion, a carefully optimized linear optical interferometer including beam splitters with variable reflectivities and a fast optical switch for the verification step. High values of our protocol benchmarks are maintained for attenuation corresponding to several kilometers of telecom optical fiber.

Experimental cheat-sensitive quantum weak coin flipping

Fri, 01 Dec 2023 00:00:00 +0000

Experimental Certification of Quantum Transmission via Bell's Theorem

Sat, 25 Nov 2023 00:00:00 +0000

Quantum transmission links are central elements in essentially all implementations of quantum information protocols. Emerging progress in quantum technologies involving such links needs to be accompanied by appropriate certification tools. In adversarial scenarios, a certification method can be vulnerable to attacks if too much trust is placed on the underlying system. Here, we propose a protocol in a device independent framework, which allows for the certification of practical quantum transmission links in scenarios where minimal assumptions are made about the functioning of the certification setup. In particular, we take unavoidable transmission losses into account by modeling the link as a completely-positive trace-decreasing map. We also, crucially, remove the assumption of independent and identically distributed samples, which is known to be incompatible with adversarial settings. Finally, in view of the use of the certified transmitted states for follow-up applications, our protocol moves beyond certification of the channel to allow us to estimate the quality of the transmitted state itself. To illustrate the practical relevance and the feasibility of our protocol with currently available technology we provide an experimental implementation based on a state-of-the-art polarization entangled photon pair source in a Sagnac configuration and analyze its robustness for realistic losses and errors.

Photonic Resources for the Implementation of Quantum Network Protocols

Fri, 02 Dec 2022 00:00:00 +0000

In this thesis, we developed a source of photonic quantum states which we use to demonstrate important cryptographic primitives, namely quantum weak coin flipping, and the certified transmission of quantum information through an untrusted and lossy quantum channel. Our source produces photon-pairs at telecom wavelengths, with high heralding efficiency and closeness to a maximally-entangled state. Pairs are used as heralded single-photons to perform the first implementation of a quantum weak coin flipping protocol, allowing two distant players to decide of a random winner. Using quantum resources allows to enforce information-theoretic security and cheat-sensitivity. Cheating players are detected in a verification step, which involves a carefully optimized linear optical interferometer including beam splitters with variable reflectivities and a fast optical switch. We demonstrate high values of our protocol benchmarks for attenuations corresponding to several kilometers of telecom optical fiber. Alternatively, photon-pairs are used as maximally-entangled qubits to certify the transmission of a single qubit through an untrusted and lossy quantum channel. We provide a whole new protocol, based on the already-known self-testing technique and new fundamental results on lossy quantum channels. We demonstrate that protocol using photon-pairs entangled in polarization to probe the channel. We show it allows the certification of quantum communication for a large amount of losses induced by the channel. Finally, we provide a novel design in order to adapt this source to multipartite entanglement generation, enabling the implementation of new protocols involving more than two players.

Photonic Resources for the Implementation of Quantum Network Protocols

Fri, 02 Dec 2022 00:00:00 +0000

The security of modern communication networks can be enhanced thanks to the laws of quantum mechanics. In this thesis, we develop a source of photon-pairs, emitted via spontaneous parametric down-conversion, which we use to demonstrate new quantum-cryptographic primitives. Pairs are used as heralded single-photons or as close-to-maximally entangled pairs. We also provide a novel design in order to adapt this source to multipartite entanglement generation. We provide the first experimental implementation of quantum weak coin flipping protocol. It allows two distant players to decide of a random winner. We demonstrate a refined and loss-tolerent version of a recently proposed theoretical protocol, using heralded single-photons mixed with vacuum to produce entanglement. It displays cheat-sensitivity, allowed by quantum interference and a fast optical switch. We also provide a new protocol for certifying the transmission of an unmeasured qubit through a lossy and untrusted channel. The security is based on new fundamental results of lossy quantum channels. We device-independently test the channel’s quality, using self-testing of Bell or steering inequalities thanks to photon-pairs entangled in polarization to probe the channel. We show it allows the certification of quantum communication for a large amount of losses induced by the channel.

Experimental cheat-sensitive quantum weak coin flipping

Thu, 17 Nov 2022 00:00:00 +0000

Quantum City: simulation of a practical near-term metropolitan quantum network

Mon, 14 Nov 2022 00:00:00 +0000

We present the architecture and analyze the applications of a metropolitan-scale quantum network that requires only limited hardware resources for end users. Using NetSquid, a quantum network simulation tool based on discrete events, we assess the performance of several quantum network protocols involving two or more users in various configurations in terms of topology, hardware and trust choices. Our analysis takes losses and errors into account and considers realistic parameters corresponding to present or near-term technology. Our results show that practical quantum-enhanced network functionalities are within reach today and can prepare the ground for further applications when more advanced technology becomes available.