Дисертації з теми "Distribution quantique de clefs"
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Denys, Aurélie. "Quantum key distribution and quantum error correction with bosonic systems." Electronic Thesis or Diss., Sorbonne université, 2024. http://www.theses.fr/2024SORUS152.
Повний текст джерелаThis thesis concerns the theoretical study of quantum key distribution and quantum error correction implemented with bosonic systems. The former is referred to as continuous-variable quantum key distribution while the latter is called bosonic error correction. In the first chapter, an analytical bound on the asymptotic secret key rate of continuous-variable quantum key distribution protocols is derived. This quantity broadly quantifies the security of a protocol. This is a significant contribution as it helps to compare the security of different instances of a protocol and to make an informed choice. In Chapter 2, a new bosonic code, the 2T-qutrit, is introduced and studied. This encoding has the particularity of using two bosonic modes, which means the space in which the information is encoded is even bigger than when only a single mode is used. This work then inspired the construction of important families of multi-mode codes, including some of the codes introduced in Chapter 3. The latter presents a general construction of error correcting codes such that the encoded information can easily be manipulated to carry out the desired logical computations
Sabban, Manuel. "Sécurité en cryptographie quantique utilisant la détection homodyne d'états cohérents à faible énergie." Phd thesis, Paris, ENST, 2009. https://pastel.hal.science/pastel-00005898.
Повний текст джерелаThe proposed word is a reflexion on security of some quantum key distribution protocols. We chose the phase of weak coherent states to support our information. Two main ideas are developped in this thesis. The first is a study of the advantages that a differential phase shift keying système with photon counter can provide, and the second is a reflexion of what a double-threshold can provide to homodyne measurements. In the part devoted to security of DPSK systems, we first compared quantitatively the security with an absolute reference scheme and that with the DPSK scheme. E show that the DPSK scheme is slightly better because the security can be considered split individually and collectively on photons. We eventually studied the security of double-threshold quantum key distribution homodyne systems. This method give access to the reliability of a measure, and allow us to choose whether or not we keep a given measurement. Different attacks have been taken into account to study achievable amount of security of systems of this kind
Sabban, Manuel. "Sécurité en cryptographie quantique utilisant la détection homodyne d'états cohérents à faible énergie." Phd thesis, Télécom ParisTech, 2009. http://pastel.archives-ouvertes.fr/pastel-00005898.
Повний текст джерелаKaiser, Florian. "Ingénierie de l'intrication photonique pour l'information quantique et l'optique quantique fondamentale." Phd thesis, Université de Nice Sophia-Antipolis, 2012. http://tel.archives-ouvertes.fr/tel-00777002.
Повний текст джерелаAgnolini, Sébastien. "Contribution à l'étude et à la réalisation d'un système de distribution quantique de clef par codage en phase." Phd thesis, Université Pierre et Marie Curie - Paris VI, 2007. http://pastel.archives-ouvertes.fr/pastel-00003416.
Повний текст джерелаAgnolini, Sébastien. "Contributions à l'étude et à la réalisation d'un système de distribution quantique de clef par codage en phase." Paris 6, 2007. https://pastel.archives-ouvertes.fr/pastel-00003416.
Повний текст джерелаBoucher, William. "Distribution quantique de clé par codage temporel." Paris 6, 2004. http://www.theses.fr/2004PA066014.
Повний текст джерелаAmblard, Zoé. "Cryptographie quantique et applications spatiales." Thesis, Limoges, 2016. http://www.theses.fr/2016LIMO0113.
Повний текст джерелаThis thesis in collaboration with Thales Alenia Space studies quantum cryptographic protocols for n parties in dimension d. We first analyze the family of Bell inequalities called homogeneous Bell inequalities introduces by François Arnault in [1] and we construct several theoretical tools for a better understanding of these inequalities. With these tools, we show how to implement the measurements required to test these inequalities by using optical devices calleds multiport beamsplitters and described by Zukowski et al. in [2]. We use these devices to construct new cryptographic protocols in dimension d called hdDEB which we describe in [3]. Then, we study advantages and drawbacks of the use of quantum cryptography to protect satellite links in a noisy environment. We consider several scenarios with LEO satellites and, for each of them, we conclude about the interest of using Quantum Key Distribution protocols
Bocquet, Aurélien. "Modèles de sécurité réalistes pour la distribution quantique de clés." Phd thesis, Paris, Télécom ParisTech, 2011. https://pastel.hal.science/pastel-00784705.
Повний текст джерелаSince its invention in 1984 by C. H. Bennett and G. Brassard, the BB84 protocol has been proven secure against the most general attacks allowed by quantum mechanics, the coherent attacks. In order to conduct such an attack, an eavesdropper needs a quantum memory. It is however technologically very hard to create a quantum memory with adequate properties at the moment. It is therefore useful to study the evolution of the power of the eavesdropper when he doesn’t have access to a perfect quantum memory but instead to a noisy quantum memory. New security models where the power of the eavesdropper is limited by the quality of its quantum memory have already been developed specifically for the study of two-party protocols like bit commitment or oblivious transfer. We therefore used these models and adapted them to the particular case of quantum key distribution. With these newly developed tools, we have studied the security of quantum key distribution protocols when the adversary doesn’t have a quantum memory and when he has access to a limited amount of noisy memory. This research improves our knowledge on the interaction between the quality of the quantum memory and the power of the attacks. It leads to a better understanding of the tradeoff between performance (measured in term of key rate or maximum distance) and security
Bocquet, Aurélien. "Modèles de sécurité réalistes pour la distribution quantique de clés." Phd thesis, Télécom ParisTech, 2011. http://pastel.archives-ouvertes.fr/pastel-00784705.
Повний текст джерелаGhalbouni, Joe. "Distribution multi-utilisateur de paires de photons intriqués aux longueurs d'onde des télécommunications." Electronic Thesis or Diss., Paris, ENST, 2013. http://www.theses.fr/2013ENST0068.
Повний текст джерелаIn order to progress towards a quantum communication network, it is vital to limit the necessary resources. In particular, we show here that we can use a single source of entangled photons pairs, to serve a large number of users. This implies that the considered source has to be spectrally broadband, and compatible with the current optical telecommunications’ infrastructure. At first, we studied a correlated photon source, based on SPDC. From the experimental values measured (counts and coincidences), an upper bound of the visibility that can be achieved in entanglement is calculated as well as the source brightness. A quality factor is established in order to compare and rank the demultiplexers tested in relation to the compromise between the quality of the quantum correlations and the source brightness.We then characterized a source of polarization entangled photon pairs. The entanglement is obtained by performing a double pumping path in a crystal of PPLN, generating a state Φ> =(1/√2)(|HH> +|VV>) . The generated photon pairs are split by using the same demultiplexers. Measurements of visibilities and the Bell parameter S are performed. The performances of the demultiplexers are compared to those obtained with the twin photons.We show that it is possible with a single source, to establish a quantum communication channel with at least 3 couples of users simultaneously. We propose at the end of this study, various methods of improvement
Leverrier, Anthony. "Etude théorique de la distribution quantique de clés à variables continues." Phd thesis, Paris, Télécom ParisTech, 2009. https://theses.hal.science/tel-00451021.
Повний текст джерелаThis thesis is concerned with quantum key distribution (QKD), a cryptographic primitive allowing two distant parties, Alice and Bob, to establish a secret key, in spite of the presence of a potential eavesdropper, Eve. Here, we focus on continuous-variable protocols, for which the information is coded in phase-space. The main advantage of these protocols is that their implementation only requires standard telecom components. The security of QKD lies on the laws of quantum physics: an eavesdropper will necessary induce some noise on the communication, therefore revealing her presence. A particularly difficult step of continuous-variable QKD protocols is the ``reconciliation'' where Alice and Bob use their classical measurement results to agree on a common bit string. We first develop an optimal reconciliation algorithm for the initial protocol, then introduce a new protocol for which the reconciliation problem is automatically taken care of thanks to a discrete modulation. Proving the security of continuous-variable QKD protocols is a challenging problem because these protocols are formally described in an infinite dimensional Hilbert space. A solution is to use all available symmetries of the protocols. In particular, we introduce and study a class of symmetries in phase space, which is particularly relevant for continuous-variable QKD. Finally, we consider finite size effects for these protocols. We especially analyse the influence of parameter estimation on the performance of continuous-variable QDK protocols
Leverrier, Anthony. "Etude théorique de la distribution quantique de clés à variables continues." Phd thesis, Télécom ParisTech, 2009. http://tel.archives-ouvertes.fr/tel-00451021.
Повний текст джерелаMeziani, Katia. "Estimation non paramétrique en tomographie quantique homodyne." Paris 7, 2008. http://www.theses.fr/2008PA077172.
Повний текст джерелаIn the setting of quantum optics, the reconstruction of the quantum state (Wigner function or infinite-dimensional density matrix) of a light beam can be seen as a statistical severely ill-posed inverse problem. First, we propose estimators of the density matrix and the Wigner function respectively, using pattern functions in the first case and kernel functions in the second. We assume that the unknown density matrix belongs to a nonparametric class which corresponds to typical states prepared in the laboratory. We translate these classes in terms of properties of the associated Wigner function. In an other part, we estimate the integrated squared Wigner function by a kernel-based second order U-statistic on a larger regularity class. This quadratic functional is a physical measure of the purity of the state. We deduce an adaptive estimator for the Wigner function that does not depend on the smoothness parameters. In the last part of the thesis, we are interested in the problem of goodness-of-fit testing. We give a testing procedure derived from a projection-type estimator on \textit{pattern} functions. We study the upper bounds of the minimax risk for all our procedures. The density matrix estimation and the testing procedure are implemented and their numerical performances are studied
Ghalbouni, Joe. "Distribution multi-utilisateur de paires de photons intriqués aux longueurs d'onde des télécommunications." Thesis, Paris, ENST, 2013. http://www.theses.fr/2013ENST0068/document.
Повний текст джерелаIn order to progress towards a quantum communication network, it is vital to limit the necessary resources. In particular, we show here that we can use a single source of entangled photons pairs, to serve a large number of users. This implies that the considered source has to be spectrally broadband, and compatible with the current optical telecommunications’ infrastructure. At first, we studied a correlated photon source, based on SPDC. From the experimental values measured (counts and coincidences), an upper bound of the visibility that can be achieved in entanglement is calculated as well as the source brightness. A quality factor is established in order to compare and rank the demultiplexers tested in relation to the compromise between the quality of the quantum correlations and the source brightness.We then characterized a source of polarization entangled photon pairs. The entanglement is obtained by performing a double pumping path in a crystal of PPLN, generating a state Φ> =(1/√2)(|HH> +|VV>) . The generated photon pairs are split by using the same demultiplexers. Measurements of visibilities and the Bell parameter S are performed. The performances of the demultiplexers are compared to those obtained with the twin photons.We show that it is possible with a single source, to establish a quantum communication channel with at least 3 couples of users simultaneously. We propose at the end of this study, various methods of improvement
Trigo, Vidarte Luis. "Design and implementation of high-performance devices for continuous-variable quantum key distribution." Thesis, Université Paris-Saclay (ComUE), 2019. http://www.theses.fr/2019SACLO021.
Повний текст джерелаQuantum key distribution (QKD) is one of the first quantum technologies that were able to provide commercially meaningful solutions to the problem of distributing cryptographic keys between trusted parties, guaranteeing long term security. It is now progressing towards technical maturity, by proposing multiple implementation alternatives. In this thesis, we study Continuous-Variables QKD (CV-QKD), which shares many common elements with classical coherent communication systems, and is a good candidate to facilitate the access to QKD for more users.The use of digital signal processing (DSP) techniques typical in classical communications has been only partially exploited in previous CV-QKD implementations. We experimentally implement standard telecommunication techniques like pulse shaping, adaptive filtering and mode recovery in order to improve the quantum secret key rate and optimize the occupied bandwidth.The potential of integration of the components in a photonic integrated circuit (PIC) is another important aspect of CV-QKD. We have tested a silicon photonics PIC integrating a 180º hybrid detector with two germanium photodiodes, showing that measured parameters are compatible with the generation of secret key.One of the most limiting factors of QKD is the performance under lossy channels, which is common in optical fibre for distances in the order of hundred kilometers. The range can be significantly extended using free space communications, and in particular satellites, where the losses at longer distances can be lower than those in fibre. We consider a model for a downlink satellite channel and predict the achievable secret key rates at different altitudes for CV-QKD, resulting in a potentially feasible technology for satellite communications, extending the range to intercontinental distances
Aymeric, Raphaël. "Convergence of quantum and classical communications." Electronic Thesis or Diss., Institut polytechnique de Paris, 2022. https://theses.hal.science/tel-03919212.
Повний текст джерелаQuantum key distribution (QKD) protocols harness fundamental quantum properties of the light to construct communication channels sensitive to eavesdropping. In order to develop the technology at large scale, one of the main challenges to overcome is the deployment cost of such systems. A significant step towards reducing deployment costs would be to use the existing optical fiber infrastructure to perform QKD, since this would relax the need to use dark (and expensive !) fiber. However this also means we must insure QKD protocols can coexist with classical communications, which can be challenging as quantum states are very sensitive to perturbations. Here, we focus particularly on continuous-variable (CV) QKD because their natural proximity to classical coherent communication systems indicates that they are good candidates for coexistence over the same fiber. Assuming CV-QKD is destined to be incorporated in classical communication links, an interesting question is whether the coexistence with classical channels will necessarily be detrimental to the CV-QKD protocol. We show that in some cases, coexistence can actually provide an advantage to the CV-QKD protocol. In a first project, we experimentally demonstrate that a classical channel can be used as a pilot signal for the quantum channel. Thus, the need for pilot-tones, mandatory in a typical CV-QKD protocol, can be relaxed. In a second project, we show that the noise generated by classical channels can be used to ”hide” the quantum signal. The quantum communication therefore can become covert thanks to the classical channels. Covert QKD protocols are interesting because they provide extreme security guarantees. We investigate the necessary conditions for covert CV-QKD as well as scenarios for its deployment in a practical setting
Lodewyck, Jérôme. "Dispositif de distribution quantique de clé avec desétats cohérents à longueur d'onde télécom." Phd thesis, Université Paris Sud - Paris XI, 2006. http://tel.archives-ouvertes.fr/tel-00130680.
Повний текст джерелаL'utilisation de variables continues dans le domaine de l'information quantique, récemment apparue, permet de concevoir des systèmes de distribution quantique de clé qui ne nécessitent que des composants standards de l'industrie des télécommunications. Ces composants ouvrent la voie vers les hauts débits caractéristiques des liaisons en fibres optiques.
Nous avons réalisé un système complet de distribution quantique de clé qui utilise l'amplitude et la phase d'états cohérents pulsés de la lumière modulées selon une distribution gaussienne. Notre système est exclusivement réalisé avec des fibres optiques, et atteint un taux de répétition de 1 MHz. Nous avons caractérisé l'information secrète transmise par ce dispositif. Nous avons validé cette caractérisation en réalisant des attaques quantiques originales qui couvrent l'ensemble des perturbations qui peuvent être envisagées sur la transmission.
Nous avons ensuite adapté des algorithmes de correction d'erreur et d'amplification de secret qui produisent une clé secrète à partir des données expérimentales. Enfin, nous avons conçu un ensemble logiciel autonome qui intègre la gestion de l'expérience aux algorithmes de correction d'erreur.
Ces travaux nous ont permis de distribuer une clé secrète sur une fibre de 25 km avec un taux finalde 1 kb/s. Le système que nous avons réalisé sera intégré dans un réseau de distribution quantique de clé faisant intervenir plusieurs collaborateurs européens.
Jouguet, Paul. "Performance et sécurité de dispositifs de distribution quantique de clés à variables continues." Thesis, Paris, ENST, 2013. http://www.theses.fr/2013ENST0048/document.
Повний текст джерелаThis thesis focuses on a cryptographic primitive that allows two distant parties to generate an arbitrary amount of secret key even in the presence of an eavesdropper, provided that they share a short initial secret message. We focus our study on continuous-variable protocols and demonstrate experimentally an all-fiber system that performs distribution of secret keys at 80 km on a dedicated fiber link while taking into account all known imperfections. We could extract secret keys at such a distance bydesigning specific error correcting codes that perform very close to Shannon’s bound for low signal to noise ratios. We also consider side-channel attacks that are not taken into account into the system security proof and propose some countermeasures. Finally, we study our system compability with intense communication channels that propagate on the same optical fiber
Jouguet, Paul. "Performance et sécurité de dispositifs de distribution quantique de clés à variables continues." Electronic Thesis or Diss., Paris, ENST, 2013. http://www.theses.fr/2013ENST0048.
Повний текст джерелаThis thesis focuses on a cryptographic primitive that allows two distant parties to generate an arbitrary amount of secret key even in the presence of an eavesdropper, provided that they share a short initial secret message. We focus our study on continuous-variable protocols and demonstrate experimentally an all-fiber system that performs distribution of secret keys at 80 km on a dedicated fiber link while taking into account all known imperfections. We could extract secret keys at such a distance bydesigning specific error correcting codes that perform very close to Shannon’s bound for low signal to noise ratios. We also consider side-channel attacks that are not taken into account into the system security proof and propose some countermeasures. Finally, we study our system compability with intense communication channels that propagate on the same optical fiber
Bloch, M. "Algorithme de réconciliation et méthodes de distribution quantique de clés adaptées au domaine fréquentiel." Phd thesis, Université de Franche-Comté, 2006. http://tel.archives-ouvertes.fr/tel-00373723.
Повний текст джерелаBloch, Matthieu. "Algorithme de réconciliation et méthodes de distribution quantique de clés adaptées au domaine fréquentiel." Phd thesis, Université de Franche-Comté, 2006. http://tel.archives-ouvertes.fr/tel-00203634.
Повний текст джерелаNous avons proposé un système de distribution quantique de clés par photons uniques exploitant un véritable codage en fréquence de l'information. Cette nouvelle méthode de codage permet de s'affranchir de dispositifs interférométriques et offre donc une grande robustesse. Un démonstrateur basé sur des composants optiques intégrés standard a été réalisé et a permis de valider expérimentalement le principe de codage. Nous avons ensuite étudié un système mettant en oeuvre un protocole de cryptographie quantique par « variables continues », codant l'information sur l'amplitude et la phase d'états cohérents. Le dispositif proposé est basé sur un multiplexage fréquentiel du signal porteur d'information et d'un oscillateur local.
Les débits atteints par les systèmes de distribution de clés ne sont pas uniquement limités par des contraintes technologiques, mais aussi par l'efficacité des protocoles de réconciliation utilisés. Nous avons proposé un algorithme de réconciliation de variables continues efficace, basé sur des codes LDPC et permettant d'envisager de réelles distributions de clés à haut débit avec les protocoles à variables continues.
Lodewyck, Jérôme. "Dispositif de distribution quantique de clé avec des états cohérents à longueur d'onde télécom." Paris 11, 2006. https://pastel.archives-ouvertes.fr/tel-00130680v2.
Повний текст джерелаPersechino, Mauro. "Étude experimentale de l'intégration d'un systèm de distribution quantique de clé à variables continues sur un circuit optique en silicium." Thesis, Université Paris-Saclay (ComUE), 2017. http://www.theses.fr/2017SACLO013/document.
Повний текст джерелаDuring recent years there have been significant developments in quantum cryptography, bringing quantum key distribution (QKD) devices on the market. This can be done by using either discrete variables (DV) and photon counting, or continuous variables (CV) and coherent detection. Current technological evolutions are now aiming at developing smaller, cheaper and more user-friendly devices.This work focuses on the implementation of CV-QKD using silicon photonics techniques, which provide a high degree of integration. This is exploited to build an on-chip realization of a cryptographic protocol, using Gaussian modulation of coherent states. Two different approaches have been used, first by physically implementing the sender (Alice) and the receiver (Bob) on the same chip for validation purposes, and then by having them onto two separate chips. The measured communication parameters give the possibility to extract a secret key
Bast, Radovan Saue Trond. "Quantum chemistry beyond the charge density." Strasbourg : Université Louis Pasteur, 2008. http://eprints-scd-ulp.u-strasbg.fr:8080/926/01/BAST_Radovan_2008.pdf.
Повний текст джерелаCohen, Ruben Y. "Thermalization of a 1-dimensional Rydberg gas and entanglement distribution across quantum networks." Thesis, Université Paris-Saclay (ComUE), 2017. http://www.theses.fr/2017SACLS281/document.
Повний текст джерелаThe collective behavior of Rydberg gases is at the heart of many proposals for quantum information. This thesis treats two distinct topics: the collective dynamic of a Rydberg ensemble and the use of quantum repeaters across quantum networks.In the first part of this thesis, we choose to focus on a simple system involving Rydberg atoms: a 1-dimensional Rydberg gas coupled to a laser resonant with the Rydberg transition. Rydberg atoms interact together through the dipole-dipole interaction. This particular feature is used for quantum information purposes, like applying multi-qubits gates for example. This interaction is strong enough so that the dynamic of such system in the regime of few excitations in the gas ensemble is already intractable without any assumptions. One of them is the hardcore Rydberg sphere assumption: we approximate this interaction by a sphere around each excitation inhibiting any second excitation within it. Another one is to suppose that the system thermalizes in such regime; a statistical treatment could then be applied. We have investigated the thermalization of a 1D-Rydberg gas and evaluated the accuracy of the microcanonical ensemble predictions under the first assumption. To do so, we have numerically simulated the dynamic of such system constituted by 100 atoms, in the regime of at most two excitations in the chain, in the initial excitation-less state. Furthermore, we constructed a 6-dimensional analytical model. Comparing the three approaches together, we have concluded that the numerical simulation and the analytical model both agree together but contradicts the microcanonical treatment. In this regime, the microcanonical ensemble is unadapted.In the second part of this thesis, we have studied the distribution of entanglement across a generic quantum network. We have mapped these quantum networks to undirected graphs and studied two different routing scenarios:- the classical routing of quantum entanglement corresponding to the scenario where clients of the network can perform only a single Bell measurement or keep a single qubit. This is the usual model of quantum repeaters. On these networks, peer-to-peer communication problems are equivalent to the vertex disjoint path problem. When the peers are chosen by an adversary, we have found two limitations due to the topological genus and the minimum degree of the graph. We have found two network architectures (almost) saturating the most constraining one, the minimum degree inequality. For the case where the peers are chosen at random, we have studied a specific graph lying in a 2- or 3-dimensional manifold and investigated the trade-off between the quantum links and the number of peers that can communicate simultaneously through the network.- true quantum routing problem (using network coding) corresponding to the situation where the quantum network is composed by small quantum processors that could apply local gates. We focus on a particular communication problem, namely the butterfly network, where classical routing is impossible. Using network coding, this communication is solved
Garcia-Patron, Sanchez Raul. "Quantum information with optical continuous variables: from Bell tests to key distribution." Doctoral thesis, Universite Libre de Bruxelles, 2007. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/210655.
Повний текст джерелаDoctorat en Sciences de l'ingénieur
info:eu-repo/semantics/nonPublished
Restrepo, Juan Sebastián. "Theory of quantum optomechanics with unconventional nonlinear coupling schemes." Paris 7, 2014. http://www.theses.fr/2014PA077228.
Повний текст джерелаIn recent years the zoology of tamed quantum systems has witnessed the arrival of a new member. In the field of optomechanical cavities it has been proven that it is possible to lead micro and nano mechanical resonators to their vibrational quantum ground state. This feat is made possible by the ability of optomechanical resonators to optically cool down the brownian motion of the mechanical degrees of freedom. We study the cooling mechanisms in optomechanical cavities subject to unconventional coupling schemes. In particular we discuss how pfiotothermal cooling leads the mechanical resonator to its ground state in regimes of parameters for which the more usual radiation pressure based cooling is unable to quench effectively enough the thermal brownian motion. On the other hand the maturity of experimental optomechanics has opened the path for the exploration of strong coupling regimes where a single photon is enough to modify the mechanical properties beyond the zero point fluctuations. Following this trend we present as well our predictions for a system combining quantum electrodynamics and quantum optomechanics. We show that by introducing an artificial two level atom inside the optomechanical cavity the cooling and amplification of mechanical motion are greatly modified. We also show how the intrinsic non-linearity of the artificial atom leads to non-classical states of the mechanical resonator
Woodhead, Erik. "Imperfections and self testing in prepare-and-measure quantum key distribution." Doctoral thesis, Universite Libre de Bruxelles, 2014. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/209185.
Повний текст джерелаThis thesis also summarises, as an appendix, a separate project which introduces and defines a hierarchy of polytopes intermediate between the local and no-signalling polytopes from the field of Bell nonlocality.
Doctorat en Sciences
info:eu-repo/semantics/nonPublished
Nguyen, Thi Hong Van. "Mesure de la distribution de l'impulsion transverse des bosons W au LHC avec le détecteur ATLAS." Paris 7, 2011. http://www.theses.fr/2011PA077158.
Повний текст джерелаMeasurements of the transverse momentum distribution of electroweak gauge bosons W and Z are one of the prior duties at the LHC. These measuremcnts providc one of the most crucial tests of Standard Model, in particular, the QCD calculations for hadron colliders, which have different approaches for different ranges of the spectrum. In addition, data on W and Z production is an important tool m searching for possible new particles, i. E. , new heavy lepton doublets, Higgs boson, or supersymmetric partners of existing particles. In this thesis we describe a measurement of the W transverse momentum (pT(W)) distribution produced by proton-proton collisions at the LHC with the ATLAS detecter. The W signature is searched via its leptonic decay modes. Because of the neutrino in the final state which is undetectable, the pT(W) must be reconstructed as the hadronic recoil measured by summing vectorially the transverse energies deposited in the calorimeter excluding those of lepton(s). We present here an algorithm of hadronic recoil reconstruction in W , Z events. The analysis is performed using the data produced at s = 7 TeV during 2010, corresponding to 31 pb-1 of integrated luminosity, in which 125k W — μv and 105k W —> ev candidates are selected. In comparison with previous measurements, this measurement at LHC with more number of events used gives a belier precision and allows to extend the range as well as apply fully correction accounting for the bin-to-bin correlation. In the measurements, the W propagator is defined us the baseline quantity to be measured. This allows for a combination of the-final-results-to— get a better statistic. The resulting combined spectrum is compared to predictions modeled by different Monte Carlo event generators and calculated from fix-order perturbative QCD by différent programs. The predictions from event generators such as ALPGEN + HERWIG, PYTHIA, RESBOS, and SHERPA match the data within 20% over the entire pT(W) range. Both fixed-order perturbative QCD predictions from the DYNNLO and MCFM programs predict fewer events at high pt(W) at O(cts ) but the agreement with the measured distribution is significantly improved by the O(as] calculations
Roumestan, François. "Techniques avancées de traitement du signal pour les systèmes de distribution quantique de clés sur fibre optique basés sur des variables continues." Electronic Thesis or Diss., Sorbonne université, 2022. https://theses.hal.science/tel-03880444.
Повний текст джерелаQuantum key distribution offers the possibility of cryptography whose security is demonstrated by the laws of quantum physics. The first commercial systems of this technology are now available. This thesis focuses on continuous variable protocols, whose practical implementation is close to modern digital transmission techniques over optical fibers. By exploiting these techniques, we realize an experimental system for high speed continuous variable quantum key distribution
Vyas, Nilesh. "Quantum cryptography in a hybrid security model." Electronic Thesis or Diss., Institut polytechnique de Paris, 2021. http://www.theses.fr/2021IPPAT049.
Повний текст джерелаExtending the functionality and overcoming the performance limitation of QKD requires either quantum repeaters or new security models. Investigating the latter option, we introduce the Quantum Computational Timelock (QCT) security model, assuming that computationally secure encryption may only be broken after time much longer than the coherence time of available quantum memories. These two assumptions, namely short-term computational security and noisy quantum storage, have so far already been considered in quantum cryptography, yet only disjointly. A practical lower bound on time, for which encryption is computationally secure, can be inferred from assumed long-term security of the AES256 encryption scheme (30 years) and the value of coherence time in experimental demonstrations of storage and then retrieval of optically encoded quantum information, at single-photon level range from a few nanoseconds to microseconds. Given the large gap between the upper bound on coherence time and lower bound on computational security time of an encryption scheme, the validity of the QCT security model can be assumed with a very high confidence today and also leaves a considerable margin for its validity in the future. Using the QCT security model, we propose an explicit d-dimensional key agreement protocol that we call MUB-Quantum Computational Timelock (MUB-QCT), where a bit is encoded on a qudit state using a full set of mutually unbiased bases (MUBs) and a family of pair-wise independent permutations. Security is proved by showing that upper bound on Eve's information scales as O(1=d). We show MUB-QCT offers: high resilience to error (up to 50% for large d) with fixed hardware requirements; MDI security as security is independent of channel monitoring and does not require to trust measurement devices. We also prove the security of the MUB-QCT protocol, with multiple photons per channel use, against non-adaptive attacks, in particular, proactive MUB measurement where eve measures each copy in a different MUB followed by post-measurement decoding. We prove that the MUB-QCT protocol allows secure key distribution with input states containing up to O(d) photons which implies a significant performance boost, characterized by an O(d) multiplication of key rate and a significant increase in the reachable distance. These results illustrate the power of the QCT security model to boost the performance of quantum cryptography while keeping a clear security advantage over classical cryptography
Ohm, Thorsten. "Effet tunnel quantique de l'aimantation dans un aimant moleculaire, Fe8." Université Joseph Fourier (Grenoble), 1998. http://www.theses.fr/1998GRE10187.
Повний текст джерелаVan, Assche Gilles. "Information-Theoretic aspects of quantum key distribution." Doctoral thesis, Universite Libre de Bruxelles, 2005. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/211050.
Повний текст джерелаLa distribution quantique de clés est une technique cryptographique permettant l'échange de clés secrètes dont la confidentialité est garantie par les lois de la mécanique quantique. Le comportement particulier des particules élémentaires est exploité. En effet, en mécanique quantique, toute mesure sur l'état d'une particule modifie irrémédiablement cet état. En jouant sur cette propriété, deux parties, souvent appelées Alice et Bob, peuvent encoder une clé secrète dans des porteurs quantiques tels que des photons uniques. Toute tentative d'espionnage demande à l'espion, Eve, une mesure de l'état du photon qui transmet un bit de clé et donc se traduit par une perturbation de l'état. Alice et Bob peuvent alors se rendre compte de la présence d'Eve par un nombre inhabituel d'erreurs de transmission.
L'information échangée par la distribution quantique n'est pas directement utilisable mais doit être d'abord traitée. Les erreurs de transmissions, qu'elles soient dues à un espion ou simplement à du bruit dans le canal de communication, doivent être corrigées grâce à une technique appelée réconciliation. Ensuite, la connaissance partielle d'un espion qui n'aurait perturbé qu'une partie des porteurs doit être supprimée de la clé finale grâce à une technique dite d'amplification de confidentialité.
Cette thèse s'inscrit dans le contexte de la distribution quantique de clé où les porteurs sont des états continus de la lumière. En particulier, une partie importante de ce travail est consacrée au traitement de l'information continue échangée par un protocole particulier de distribution quantique de clés, où les porteurs sont des états cohérents de la lumière. La nature continue de cette information implique des aménagements particuliers des techniques de réconciliation, qui ont surtout été développées pour traiter l'information binaire. Nous proposons une technique dite de réconciliation en tranches qui permet de traiter efficacement l'information continue. L'ensemble des techniques développées a été utilisé en collaboration avec l'Institut d'Optique à Orsay, France, pour produire la première expérience de distribution quantique de clés au moyen d'états cohérents de la lumière modulés continuement.
D'autres aspects importants sont également traités dans cette thèse, tels que la mise en perspective de la distribution quantique de clés dans un contexte cryptographique, la spécification d'un protocole complet, la création de nouvelles techniques d'amplification de confidentialité plus rapides à mettre en œuvre ou l'étude théorique et pratique d'algorithmes alternatifs de réconciliation.
Enfin, nous étudions la sécurité du protocole à états cohérents en établissant son équivalence à un protocole de purification d'intrication. Sans entrer dans les détails, cette équivalence, formelle, permet de valider la robustesse du protocole contre tout type d'espionnage, même le plus compliqué possible, permis par les lois de la mécanique quantique. En particulier, nous généralisons l'algorithme de réconciliation en tranches pour le transformer en un protocole de purification et nous établissons ainsi un protocole de distribution quantique sûr contre toute stratégie d'espionnage.
Quantum key distribution is a cryptographic technique, which allows to exchange secret keys whose confidentiality is guaranteed by the laws of quantum mechanics. The strange behavior of elementary particles is exploited. In quantum mechnics, any measurement of the state of a particle irreversibly modifies this state. By taking advantage of this property, two parties, often called Alice and bob, can encode a secret key into quatum information carriers such as single photons. Any attempt at eavesdropping requires the spy, Eve, to measure the state of the photon and thus to perturb this state. Alice and Bob can then be aware of Eve's presence by a unusually high number of transmission errors.
The information exchanged by quantum key distribution is not directly usable but must first be processed. Transmission errors, whether they are caused by an eavesdropper or simply by noise in the transmission channel, must be corrected with a technique called reconciliation. Then, the partial knowledge of an eavesdropper, who would perturb only a fraction of the carriers, must be wiped out from the final key thanks to a technique called privacy amplification.
The context of this thesis is the quantum key distribution with continuous states of light as carriers. An important part of this work deals with the processing of continuous information exchanged by a particular protocol, where the carriers are coherent states of light. The continuous nature of information in this case implies peculiar changes to the reconciliation techniques, which have mostly been developed to process binary information. We propose a technique called sliced error correction, which allows to efficiently process continuous information. The set of the developed techniques was used in collaboration with the Institut d'Optique, Orsay, France, to set up the first experiment of quantum key distribution with continuously-modulated coherent states of light.
Other important aspects are also treated in this thesis, such as placing quantum key distribution in the context of a cryptosystem, the specification of a complete protocol, the creation of new techniques for faster privacy amplification or the theoretical and practical study of alternate reconciliation algorithms.
Finally, we study the security of the coherent state protocol by analyzing its equivalence with an entanglement purification protocol. Without going into the details, this formal equivalence allows to validate the robustness of the protocol against any kind of eavesdropping, even the most intricate one allowed by the laws of quantum mechanics. In particular, we generalize the sliced error correction algorithm so as to transform it into a purification protocol and we thus establish a quantum key distribution protocol secure against any eavesdropping strategy.
Doctorat en sciences appliquées
info:eu-repo/semantics/nonPublished
Qin, Hao. "Sécurité pratique de systèmes de cryptographie quantique : étude d'attaques et développement de contre-mesures." Electronic Thesis or Diss., Paris, ENST, 2015. http://www.theses.fr/2015ENST0040.
Повний текст джерелаIn this thesis, I study a cryptographic primitive called quantum key distribution which allows two remote parties to share a secret key, in the presence of an eavesdropper, whose power is only limited by the laws of quantum physics. I focus my study on the implementation and the practical security of continuousvariable protocols. For the first time, I have proposed and studied a detector-based side channel attack on a continuous-variable system : saturation attack. This attack opens a new security loophole that we have characterized experimentally in our laboratory, on a real continuous-variable system. Finally, we have demonstrated experimentally for the first time the feasibility of a continuous-variable system deployment in a Dense Wavelength Division Multiplexing network, where quantum signals coexist with intense classical signals in a same fiber
Dillet, Valérie. "Simulation des effets de solvant dans les calculs quantiques de structure moléculaire." Nancy 1, 1993. http://www.theses.fr/1993NAN10123.
Повний текст джерелаPalau, Jean-Marc. "Corrélations entre données nucléaires et expériences intégrales à plaques : le cas du hafnium." Aix-Marseille 1, 1997. http://www.theses.fr/1997AIX11038.
Повний текст джерелаGhorai, Shouvik. "Continuous-variable quantum cryptographic protocols." Electronic Thesis or Diss., Sorbonne université, 2021. https://accesdistant.sorbonne-universite.fr/login?url=https://theses-intra.sorbonne-universite.fr/2021SORUS007.pdf.
Повний текст джерелаThis thesis is concerned with the study and analysis of two quantum cryptographic protocols: quantum key distribution (QKD) and unforgeable quantum money in the continuous-variable (CV) framework. The main advantage of CV protocols is that their implementation only requires standard telecom components. QKD allows two distant parties, Alice and Bob, to establish a secure key, even in the presence of an eavesdropper, Eve. The remarkable property of QKD is that its security can be established in the information-theoretic setting, without appealing to any computational assumptions. Proving the security of CV-QKD protocols is challenging since the protocols are described in an infinite-dimensional Fock space. One of the open questions in CV-QKD was establishing security for two-way QKD protocols against general attacks. We exploit the invariance of Unitary group U(n) of the protocol to establish composable security against general attacks. We answer another pressing question in the field of CV-QKD with a discrete modulation by establishing the asymptotic security of such protocols against collective attacks. We provide a general technique to derive a lower bound on the secret key rate by formulating the problem as a semidefinite program. Quantum money exploits the no-cloning property of quantum mechanics to generate unforgeable tokens, banknotes, and credit cards. We propose a CV private-key quantum money scheme with classical verification. The motivation behind this protocol is to facilitate the process of practical implementation. Previous classical verification money schemes use single-photon detectors for verification, while our protocols use coherent detection
AL, SALEH-MAHROUSSEH SALOUA. "Calcul relativiste, en electrodynamique quantique, de la diffusion compton sur un electron lie." Clermont-Ferrand 2, 1988. http://www.theses.fr/1988CLF21098.
Повний текст джерелаMarulanda, Acosta Valentina. "Quantum Key Distribution through atmospheric turbulence : secure satellite-to-ground links." Electronic Thesis or Diss., Sorbonne université, 2023. http://www.theses.fr/2023SORUS378.
Повний текст джерелаThe 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
Fossier, Simon. "Mise en œuvre et évaluation de dispositifs de cryptographie quantique à longueur d'onde télécom." Phd thesis, Université Paris Sud - Paris XI, 2009. http://tel.archives-ouvertes.fr/tel-00429450.
Повний текст джерелаAtas, Yasar Yilmaz. "Quelques aspects du chaos quantique dans les systèmes de N-corps en interaction : chaînes de spins quantiques et matrices aléatoires." Thesis, Paris 11, 2014. http://www.theses.fr/2014PA112221/document.
Повний текст джерелаMy thesis is devoted to the study of some aspects of many body quantum interacting systems. In particular we focus on quantum spin chains. I have studied several aspects of quantum spin chains, from both numerical and analytical perspectives. I addressed especially questions related to the structure of eigenfunctions, the level densities and the spectral properties of spin chain Hamiltonians. In this thesis, I first present the basic numerical techniques used for the computation of eigenvalues and eigenvectors of spin chain Hamiltonians. Level densities of quantum models are important and simple quantities that allow to characterize spectral properties of systems with large number of degrees of freedom. It is well known that the level densities of most integrable models tend to the Gaussian in the thermodynamic limit. However, it appears that in certain limits of coupling of the spin chain to the magnetic field and for finite number of spins on the chain, one observes peaks in the level density. I will show that the knowledge of the first two moments of the Hamiltonian in the degenerate subspace associated with each peak give a good approximation to the level density. Next, I study the statistical properties of the eigenvalues of spin chain Hamiltonians. One of the main achievements in the study of the spectral statistics of quantum complex systems concerns the universal behaviour of the fluctuation of measure such as the distribution of spacing between two consecutive eigenvalues. These fluctuations are very well described by the theory of random matrices but the comparison with the theoretical prediction generally requires a transformation of the spectrum of the Hamiltonian called the unfolding procedure. For many-body quantum systems, the size of the Hilbert space generally grows exponentially with the number of particles leading to a lack of data to make a proper statistical study. These constraints have led to the introduction of a new measure free of the unfolding procedure and based on the ratio of consecutive level spacings rather than the spacings themselves. This measure is independant of the local level density. By following the Wigner surmise for the computation of the level spacing distribution, I obtained approximation for the distribution of the ratio of consecutive level spacings by analyzing random 3x3 matrices for the three canonical ensembles. The prediction are compared with numerical results showing excellent agreement. Finally, I investigate eigenfunction statistics of some canonical spin-chain Hamiltonians. Eigenfunctions together with the energy spectrum are the fundamental objects of quantum systems: their structure is quite complicated and not well understood. Due to the exponential growth of the size of the Hilbert space, the study of eigenfunctions is a very difficult task from both analytical and numerical points of view. I demonstrate that the groundstate eigenfunctions of all canonical models of spin chain are multifractal, by computing numerically the Rényi entropy and extrapolating it to obtain the multifractal dimensions
Ducloué, Bertrand. "Tests phénoménologiques de la chromodynamique quantique perturbative à haute énergie au LHC." Phd thesis, Université Paris Sud - Paris XI, 2014. http://tel.archives-ouvertes.fr/tel-01057271.
Повний текст джерелаHarraud, Pierre-Antoine. "Étude de la structure du nucléon par des calculs de QCD sur réseau avec des fermions de masse twistée." Grenoble, 2010. http://www.theses.fr/2010GRENY057.
Повний текст джерелаUnderstanding the structure of the nucleon from Quantum ChromoDynamics is one of the greatest challenges of hadronic physics. Only lattice QCD allows to determine numerically the values of the observables from ab-initio principles. This thesis aims to study the nucleon form factors and the first moments of partons distribution fnctions by using a discretized action with twisted mass fermions. As a main advantage, the discretization effects are suppressed at first order in the lattice spacing. In addition, the set of simulations allows a good control of the systematical errors. After reviewing the computation technics, the results obtained for a wide range of parameters are presented, with lattice spacings varying from 0. 0056 fm to 0. 089 fm, spatial volumes from 2. 1 up to 2. 7 fm and several pion masses in the range of 260-470 MeV. The vector renormalization constant was determined in the nucleon sector with improved precision. Concerning the electric charge radius, we found a finite volume effect that provides a key towards an explanation of the chiral dependence to the physical point. The results for the magnetic moment, the axila charge, the magnetic and axial charge radii, the momentum and spin fractions carried by the quarks show no dependence on the lattice spacing nor volume. In our range of pion masses, their values show a deviationfrom the experimental values. Their chiral behaviour do not exhibit the curvature predicted by the chiral perturbation theory which could explain the apparent discrepancy
Nasserdine, Mohamed M'Madi. "Mesure de la distribution du champ en chambre réverbérante par la théorie des perturbations : application à l'étude des directions d'arrivée." Thesis, Paris Est, 2015. http://www.theses.fr/2015PESC1026/document.
Повний текст джерелаThis work deals with field measurement techniques in large electromagnetic enclosures namely reverberation chambers. Due to the perturbation of the field distribution within a resonant cavity due to the presence of an introduced object, conventional field measurement techniques employing an antenna suffer from a limited accuracy. Therefore we propose a new measurement technique of the electric field distribution based on the perturbation theory; it consists of a measure of the cavity resonant frequency variation when displacing a small perturbing object within the cavity, and leads to the electric field distribution. The choice of the perturbing object shape, dimension and material is discussed with the help of simulation and measurement results in a canonical case in order to adapt the measurement setup to the studied case. This technique is then successfully employed in a reverberation chamber equipped with a mode stirrer, as well as to measure the field within a metallic box placed in the cavity. Using a post-processing based on MUSIC algorithm, this approach has permitted to determine accurately the field directions-of-arrival in the reverberation chamber
Boucher, Guillaume. "Biphoton Frequency-Correlations Engineering and Measurement with a Semiconductor Microcavity." Sorbonne Paris Cité, 2016. http://www.theses.fr/2016USPCC071.
Повний текст джерелаThis work is focused on the engineering and characterization of the frequency-time properties of photon pairs generated with a semiconductor source. This device emits photons propagating in opposite directions at telecom wavelengths using spontaneous parametric down-conversion at room temperature. A microcavity integrated in the source allows the resonance of the transverse pump beam, enhancing the efficiency of the nonlinear interaction. We give a theoretical description of the down-conversion process in the source and we show how the spatial and spectral properties of the pump beam impact the properties of the photons, in particular their degree of entanglement in frequency allowing a versatile engineering. The variety of states that can be produced is illustrated using the Joint Spectral Amplitude. Two techniques allowing the characterization of the Joint Spectral Intensity have been implemented. The first one is a single photon spectrograph. The second one, based on the stimulation of the down-conversion process showed a dramatic improvement in terms of resolution and integration time. Both techniques allowed the demonstration of the frequency correlation engineering by varying the waist and curvature radius of the pump beam. Examples of more exotic states and a technique to characterize their chronocyclic Wigner function are theoretically investigated. The relationship between time-frequency properties and degree of entanglement in polarization of the biphoton is also explored
Aubert, Flavien. "Étude conjointe par calculs ab-initio et analyse de la densité électronique du composé moléculaire (EDO-TTF)₂-PF₆ présentant une transition métal-isolant." Rennes 1, 2008. http://www.theses.fr/2008REN1S146.
Повний текст джерелаDuring this work, we have investigated, using DFT calculation and topological analysis of the electron density, the metal to insulator phase transition occuring in the organic compound (EDO-TTF)2PF6. This phase transition takes place at 278K but can also be photo-induced on pico-second time scale. It also exhibits many different aspects of phase transition : Peierls like instability, exotic 0 +1 +1 0 charge ordering of EDO-TTF tetramers and orientational ordering of PF6 ions. Using high and low temperature band structure as well as bond critical points analysis we could fit a tight-binding model to ab-initio calculations from which we have been able to find and characterize the charge density wave and propose a transition mechanism governed by coulombic interactions
Reymond, Georges-Olivier. "Etudes expérimentales d'atomes dans un piège dipolaire microscopique." Phd thesis, Université Paris Sud - Paris XI, 2002. http://tel.archives-ouvertes.fr/tel-00002178.
Повний текст джерелаBouhmaida, Nouzha. "Modélisation du potentiel électrostatique calcule a partir de la densité électronique de déformation X-X dans les cristaux moléculaires : application aux composés peptidiques." Nancy 1, 1993. http://www.theses.fr/1993NAN10288.
Повний текст джерелаBast, Radovan. "Quantum chemistry beyond the charge density." Université Louis Pasteur (Strasbourg) (1971-2008), 2008. https://publication-theses.unistra.fr/public/theses_doctorat/2008/BAST_Radovan_2008.pdf.
Повний текст джерелаThis thesis focuses on the calculation and visualization of molecular properties within the 4-component relativistic framework. Response theory together with density functional theory (DFT) within the Kohn-Sham approach are the main tools. The implementation of closed-shell linear and quadratic response functions within time-dependent DFT in the 4-component relativistic framework is presented with extensions that include contributions from the spin density. This thesis contains the first 4-component relativistic Hartree-Fock study of parity-violating effects on nuclear magnetic resonance parameters. An analytical real-space approach to frequency-dependent second-order molecular properties within the 4-component relativistic framework is introduced together with tools for the visualization of higher-order molecular properties based on the finite perturbation approach