Laura Dos Santos Martins | LIP6 - Équipe QI

Implementation of Protocols for Quantum Photonic Networks

Thu, 27 Mar 2025 00:00:00 +0000

Félicitations Dr. dos Santos Martins !

Résumé

This thesis is situated in the field of quantum information, with a particular focus on quantum communication networks. The goal of such networks is to enable fundamentally new technologies by facilitating quantum communication between distant parties, eventually leading to a Quantum Internet. These networks allow the transmission of quantum bits (qubits) over long distances, enabling tasks that are provably impossible for any classical communication network. Furthermore, the ability to generate entanglement between remote sites provides a powerful platform for fundamental studies of nature. Photonic resources are central to quantum network infrastructures, as they provide the optimal means for communication between the network nodes. In this thesis, we implement a photonic platform capable of generating high-fidelity Greenberger–Horne–Zeilinger (GHZ) states at telecom wavelengths in a compact and scalable configuration. Our source relies on spontaneous parametric down-conversion within a layered Sagnac interferometer, requiring only a single nonlinear crystal. This design enables the generation of highly indistinguishable photon pairs, leading to high-quality multipartite entangled states. Using this source, we provide the first experimental demonstration of quantum state certification in a device-independent framework, where the quantum states are not assumed to be identically and independently distributed (non-IID regime). This task is a fundamental building block for quantum communication and computation, as it determines whether the involved parties can trust their resources or whether the application should be aborted. We further investigate the efficiency of this protocol with respect to the amount of resources required and analyze how it can be leveraged for robust and reliable quantum information processing. Additionally, we explore the privacy of individual parties in a distributed quantum sensing protocol by certifying the entangled states shared within the network. Our work broadens and enriches the application scope of quantum communication networks.

Implementation of Protocols for Quantum Photonic Networks

Thu, 27 Mar 2025 00:00:00 +0000

This thesis is situated in the field of quantum information, with a particular focus on quantum communication networks. The goal of such networks is to enable fundamentally new technologies by facilitating quantum communication between distant parties, eventually leading to a Quantum Internet. These networks allow the transmission of quantum bits (qubits) over long distances, enabling tasks that are provably impossible for any classical communication network. Furthermore, the ability to generate entanglement between remote sites provides a powerful platform for fundamental studies of nature. Photonic resources are central to quantum network infrastructure, as they provide the optimal means for communication between the network nodes. In this thesis, we implement a photonic platform design capable of generating high-fidelity Greenberger-Horne-Zeilinger (GHZ) states at telecom wavelengths in a compact and scalable configuration. Our source relies on spontaneous parametric down-conversion within a layered Sagnac interferometer, requiring only a single nonlinear crystal. This design enables the generation of highly indistinguishable photon pairs, leading to high-quality multipartite entangled states. Using this source, we provide the first experimental demonstration of device-independent quantum state certification in the non-IID regime. This task is a fundamental building block for quantum communication and computation, as it determines whether the involved parties can trust their resources or whether the application should be aborted. We further investigate the sample efficiency of this protocol and analyze how it can be leveraged for robust and reliable quantum information processing. Additionally, we explore the privacy of individual parties in a distributed quantum sensing protocol by certifying the entangled states shared within the network.

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.

Experimental Sample-Efficient and Device-Independent GHZ State Certification

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

The certification of quantum resources is a critical tool in the development of quantum information processing. In particular, quantum state verification is a fundamental building block for communication and computation applications, determining whether the involved parties can trust the resources at hand or whether the application should be aborted. Self-testing methods have been used to tackle such verification tasks in a device-independent (DI) setting. However, these approaches commonly consider the limit of large (asymptotic), identically and independently distributed (IID) samples, which weakens the DI claim and poses serious challenges to their experimental implementation. Here we overcome these challenges by adopting a theoretical protocol enabling the certification of quantum states in the few-copies and non-IID regime and by leveraging a high-fidelity multipartite entangled photon source. This allows us to show the efficient and device-independent certification of a single copy of a four-qubit GHZ state that can readily be used for the robust and reliable implementation of quantum information tasks.

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 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.