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Širjov, Jakub. "Testovací polygon pro kvantovou distribuci klíčů." Master's thesis, Vysoké učení technické v Brně. Fakulta elektrotechniky a komunikačních technologií, 2021. http://www.nusl.cz/ntk/nusl-442371.
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The aim of this masters thesis is to explain quantum key distribution (QKD) and principle of signal transmission in the quantum channel. Further this thesis complains commercial distributors of QKD technologies and their individual appliances. Practical part of the thesis is separated to 3 parts. First part handles transmission of quantum keys in QKDNetsim simulator. Second part takes care of design and creation of a test polygon that allows for testing of many optical network configurations with quantum signal and normal data traffic being transmitted in a single fiber. Multiple simulations of use of various filter types to supress the signal noise in the program VPIphotonics and tested by QKDNetsim are shown in the last part of this thesis.
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Gariano, John, and Ivan B. Djordjevic. "PPLN-waveguide-based polarization entangled QKD simulator." SPIE-INT SOC OPTICAL ENGINEERING, 2017. http://hdl.handle.net/10150/626494.
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We have developed a comprehensive simulator to study the polarization entangled quantum key distribution (QKD) system, which takes various imperfections into account. We assume that a type-II SPDC source using a PPLN-based nonlinear optical waveguide is used to generate entangled photon pairs and implements the BB84 protocol, using two mutually unbiased basis with two orthogonal polarizations in each basis. The entangled photon pairs are then simulated to be transmitted to both parties; Alice and Bob, through the optical channel, imperfect optical elements and onto the imperfect detector. It is assumed that Eve has no control over the detectors, and can only gain information from the public channel and the intercept resend attack. The secure key rate (SKR) is calculated using an upper bound and by using actual code rates of LDPC codes implementable in FPGA hardware. After the verification of the simulation results, such as the pair generation rate and the number of error due to multiple pairs, for the ideal scenario, available in the literature, we then introduce various imperfections. Then, the results are compared to previously reported experimental results where a BBO nonlinear crystal is used, and the improvements in SKRs are determined for when a PPLN-waveguide is used instead.
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Lydersen, Lars Vincent van De Wiel. "Security of QKD-systems with detector efficiency mismatch." Thesis, Norwegian University of Science and Technology, Department of Electronics and Telecommunications, 2008. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-9808.
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The rules of quantum mechanics makes it possible to exchange a secret key at a distance. This is called quantum key distribution (QKD). In theory the key exchange can be made completely secure. Real QKD implementations however, has numerous imperfections. Luckily one has also been able to prove the security of QKD with a large variety of imperfections. The field of QKD has matured over the recent years, and it has now reached commercial applications with photons as the quantum bits, and optical fibers as the quantum channel. Today there are at least three commercial vendors of QKD-systems. We live in the times of quantum hacking. Researchers has begun the task of breaking the security of QKD-systems. Many new imperfections has been discovered, some of which might be used to break the security of QKD. This thesis is a study of the detector efficiency mismatch loophole. Most QKD-systems require two detectors, and it is virtually impossible to make two identical detectors with the exact same efficiency. What is worse, it turns out that the eavesdropper can often control the relative efficiencies of the two detectors trough some domain, for instance by controlling the timing, the frequency or the spacial mode of the photons. This can in turn be used by the eavesdropper to gain information about the secret key. Previously the best known attack would compromise security if the detector efficiency mismatch of about 1:15. Here the current attacks on systems with detector efficiency mismatch are improved to compromise security for a mismatch of about 1:4. This is less than the mismatch found in a commercial QKD-system, so the attack could in principle be used to eavesdrop on this QKD-system. One might try to close the loophole by modifying the implementation. One suggestion is the four state Bob. The problem is that this patch will in turn open other loopholes, and one of these loopholes reopen the detector efficiency mismatch loophole. One can remove Eves information about the key by doing a sufficient amount of extra privacy amplification. Here a general security bound is presented, quantifying the required amount of extra privacy amplification to remove Eve's information about the key. The proof is more general than the previous security proof, and is valid for any basis dependent, possibly lossy, linear optical imperfections in the channel and receiver/detectors. Since this is more realistic assumptions for a QKD-implementation, the proof represents a major step of closing the loophole in real devices.
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Nishat, Md Rezaul Karim. "DESIGN OF NANOSTRUCTURED ENTANGLED PHOTON PAIR GENERATOR FOR QKD APPLICATIONS." OpenSIUC, 2018. https://opensiuc.lib.siu.edu/dissertations/1580.
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Finite structure splitting (FSS) is a bottleneck for quantum dot (QD) based solid state entangled photon pair generator (EPPG) for Quantum Key Distribution (QKD) application. In QD, entangle photon pairs are generated through a cascaded emission process—biexciton to exciton to ground state. The FSS of the excitonic state destroys the entanglement of the photon pairs, hence needs to be eliminated. FSS can be tuned by engineering the crystal growth direction, varying dot shape or size, changing the material composition and/or applying external strain. Numerical investigation of FSS and designing of realistically-sized QD based EPPG demands multiscale-multiphysics many-body simulation efforts. To this end, in this work, we report the coupling of full configuration integration (FCI) method with the atomistic empirical tight-binding (TB) models (10-band sp3s* and 20-band sp3d5s*) to calculate the excitonic energetics and FSS in recently reported multimillion-atom III-V dot-in-nanowire structures. The core of the computational framework comprises two parts: i) NEMO3D, which, using the TB models, can compute single-electron energetics of multimillion-atom structures, and ii) An FCI kernel, which computes the many-particle energetics and wavefunctions using the single-electron outputs as derived from NEMO3D. NEMO3D is a broad platform that handles geometry construction, calculation of strain distributions and built-in potential fields, solving the Schrodinger’s equation and computing optical matrix elements. Three output files from NEMO3D are of particular importance for the FCI toolkit: i) Single-electron energy values, ii) Eigen functions, and iii) Relaxed atom positions of the device. FCI calculates the Coulomb and Exchange matrix elements associated with multi-particles and forms the many-body Hamiltonian. The excitonic states (electron-hole pair) are calculated by solving the many-body Hamiltonian and the value of FSS, if exists, is determined. Recently, nitride-based nanostructured devices have been found to be a promising candidate for single and entangled multi-photon emitter applications. The principal goal of this dissertation is to facilitate the numerical design of InGaN/GaN based dot-in-nanowire EPPG units. To this end, a number of kernels in NEMO3D and FCI packages were augmented. The geometry constructor in NEMO3D was extended for two non-polar planes of wurtzite crystal: m-plane and a-plane. It is found that these two non-polar planes, with much smaller built-in piezoelectric fields, exhibit improved optical transition probabilities than the polar c-plane counterpart. As test cases, light-emitters in dot-in-wire and multiple quantum well (MQW) configurations were simulated and compared in all three (c-plane, m-plane, and a-plane) growth directions. TCAD toolkits are used to simulate the terminal optical characteristics such as internal quantum efficiency (IQE) and spontaneous emission rate. Hexagonal-base truncated-pyramid shaped QD was also added to the NEMO3D geometry constructor as pyramid shaped dots offer directionality and better extraction efficiency of emitted photons, which is important for single or entangled photon generators. The FCI simulator was modified for calculating the excitonic states that involve an electron-hole pair. As for EPPG design, four device structures are considered: i) Disk-in-nanowire on the polar c-plane, ii) pyramid shaped dot-in-nanowire on polar c-plane, iii) Disk-in-nanowire on non-polar m-plane, and iv) Disk-in-nanowire on non-polar a-plane. Simulations are done for different disk thicknesses, material compositions, quantum dot shapes and crystal directions. Results and in-depth analysis are presented on the effects of these design parameters on many-body energetics e.g. binding energy, excitonic bandgaps and FSS. The derivation of excitonic transition probability from single-electron momentum matrix is discussed in detail. Finally, an EPPG design is proposed employing the entangled polarization profiles from two excitonic emissions.
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Gariano, John, and Ivan B. Djordjevic. "Multimode entanglement assisted QKD through a free-space maritime channel." SPIE-INT SOC OPTICAL ENGINEERING, 2017. http://hdl.handle.net/10150/626495.
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When using quantum key distribution (QKD), one of the trade-offs for security is that the generation rate of a secret key is typically very low. Recent works have shown that using a weak coherent source allows for higher secret key generation rates compared to an entangled photon source, when a channel with low loss is considered. In most cases, the system that is being studied is over a fiber-optic communication channel. Here a theoretical QKD system using the BB92 protocol and entangled photons over a free-space maritime channel with multiple spatial modes is presented. The entangled photons are generated from a spontaneous parametric down conversion (SPDC) source of type II. To employ multiple spatial modes, the transmit apparatus will contain multiple SPDC sources, all driven by the pump lasers assumed to have the same intensity. The receive apparatuses will contain avalanche photo diodes (APD), modeled based on the NuCrypt CPDS-1000 detector, and located at the focal point of the receive aperture lens. The transmitter is assumed to be located at Alice and Bob will be located 30 km away, implying no channel crosstalk will be introduced in the measurements at Alices side due to turbulence. To help mitigate the effects of atmospheric turbulence, adaptive optics will be considered at the transmitter and the receiver. An eavesdropper, Eve, is located 15 km from Alice and has no control over the devices at Alice or Bob. Eve is performing the intercept resend attack and listening to the communication over the public channel. Additionally, it is assumed that Eve can correct any aberrations caused by the atmospheric turbulence to determine which source the photon was transmitted from. One, four and nine spatial modes are considered with and without applying adaptive optics and compared to one another.
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Gasparoux, Philippe. "Valeur pronostique de la mesure ambulatoire de l'intervalle QKD chez l'hypertendu." Bordeaux 2, 1996. http://www.theses.fr/1996BOR2M028.
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Mas, Denis. "Intérêt et reproductibilité d'un protocole standardisé dans la mesure de l'intervalle QKd." Bordeaux 2, 1997. http://www.theses.fr/1997BOR23069.
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Level, Claude. "Etude de la compliance artérielle chez l'hémodialysé chronique par la mesure de l'intervalle QKd." Bordeaux 2, 1998. http://www.theses.fr/1998BOR23026.
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Sun, Xiaole, Ivan B. Djordjevic, and Mark A. Neifeld. "Multiple spatial modes based QKD over marine free-space optical channels in the presence of atmospheric turbulence." OPTICAL SOC AMER, 2016. http://hdl.handle.net/10150/622480.
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We investigate a multiple spatial modes based quantum key distribution (QKD) scheme that employs multiple independent parallel beams through a marine free-space optical channel over open ocean. This approach provides the potential to increase secret key rate (SKR) linearly with the number of channels. To improve the SKR performance, we describe a back-propagation mode (BPM) method to mitigate the atmospheric turbulence effects. Our simulation results indicate that the secret key rate can be improved significantly by employing the proposed BPM-based multi-channel QKD scheme. (C) 2016 Optical Society of America
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Djordjevic, Ivan B. "Integrated Optics Modules Based Proposal for Quantum Information Processing, Teleportation, QKD, and Quantum Error Correction Employing Photon Angular Momentum." IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 2016. http://hdl.handle.net/10150/615122.
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To address key challenges for both quantum communication and quantum computing applications in a simultaneous manner, we propose to employ the photon angular momentum approach by invoking the well-known fact that photons carry both the spin angular momentum (SAM) and the orbital angular momentum (OAM). SAM is associated with polarization, while OAM is associated with azimuthal phase dependence of the complex electric field. Given that OAM eigenstates are mutually orthogonal, in principle, an arbitrary number of bits per single photon can be transmitted. The ability to generate/analyze states with different photon angular momentum, by using either holographic or interferometric methods, allows the realization of quantum states in multidimensional Hilbert space. Because OAM states provide an infinite basis state, while SAM states are 2-D only, the OAM can also be used to increase the security for quantum key distribution (QKD) applications and improve computational power for quantum computing applications. The goal of this paper is to describe photon angular momentum based deterministic universal quantum qudit gates, namely, {generalized-X, generalized-Z, generalized-CNOT} qudit gates, and different quantum modules of importance for various applications, including (fault-tolerant) quantum computing, teleportation, QKD, and quantum error correction. For instance, the basic quantum modules for quantum teleportation applications include the generalized-Bell-state generation module and the QFT-module. The basic quantum module for quantum error correction and fault-tolerant computing is the nonbinary syndrome calculator module. The basic module for entanglement assisted QKD is either the generalized-Bell-state generation module or the Weyl-operator-module. The possibility of implementing all these modules in integrated optics is discussed as well. Finally, we provide security analysis of entanglement assisted multidimensional QKD protocols, employing the proposed qudit modules, by taking into account the imperfect generation of OAM modes.
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Calisti, Davide. "Performance Analysis and Multi-hop Protocols for Quantum Cryptography based on BB84." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2017.
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Quantum cryptography and its well-known application, quantum key distribution (QKD), promises unconditional security in data communications and is currently being deployed in commercial applications. However, there exist several challenges that concern QKD, such as secret key rate, distance, security and cost. The work of this thesis is at first developed by studying the best-know QKD protocol (BB84). The study provides performance analysis of the protocol over a quantum bit-flip channel in presence of eavesdropping, in terms of detection and false alarm probabilities, with an extension to the case of a generic quantum noisy channel. Finally, the problem of exchanging keys over long distances has been analized, providing a Multi-Hop protocol without using intercept-resend relays, and its extension to the case of a trusted node network, that exploits QKD only locally to establish secrets keys.
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Vallot, Michaël. "Etude des troubles de la compliance artérielle par le biais de la mesure de l'intervalle QKD chez des patients opérés avec succés d'une coarctation de l'aorte." Bordeaux 2, 1999. http://www.theses.fr/1999BOR23034.
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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.
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Quantum key distribution (QKD) protocols are intended to allow cryptographic keys to be generated and distributed in way that is provably secure based on inherent limitations, such as the no-cloning principle, imposed by quantum mechanics. This unique advantage compared with classical cryptography comes with an added difficulty: key bits in QKD protocols are encoded in analogue quantum states and their preparation is consequently subject to the usual imprecisions inevitable in any real world experiment. The negative impact of such imprecisions is illustrated for the BB84 QKD protocol. Following this, the main part of this thesis is concerned with the incorporation of such imprecisions in security proofs of the BB84 and two semi-device-independent protocols against the class of collective attacks. On a technical level, by contrast with the vast majority of security proofs developed since the turn of the century, in which recasting the protocol into an equivalent entanglement-based form features heavily in the analysis, the main results obtained here are approached directly from the prepare-and-measure perspective and in particular the connection with the no-cloning theorem and an early security proof by Fuchs et al. against the class of individual attacks is emphasised.This 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
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Berarducci, Martina. "E91: un protocollo crittografico basato sulla Disuguaglianza di Bell." Bachelor's thesis, Alma Mater Studiorum - Università di Bologna, 2019. http://amslaurea.unibo.it/18220/.
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L'elaborato si propone di analizzare nel dettaglio il protocollo di crittografia quantistica E91 ideato da Artur Ekert. Esso consiste in un protocollo di distribuzione delle chiavi (QKD) che permette di arrivare alla condivisione della chiave segreta, poi utilizzata per comunicare grazie a sistemi crittografici a chiave privata, come il noto cifrario di Vernam. Nella prima parte sono introdotte le nozioni di crittografia classica e i concetti di sicurezza necessari per comprendere il funzionamento del cifrario di Vernam, l'unico cifrario a sicurezza perfetta dimostrabile matematicamente. A seguire viene introdotta la meccanica quantistica, a partire dall'esperimento di Stern e Gerlach, in grado di mettere in evidenza alcuni degli aspetti chiave della teoria. Dopo un breve cenno alla notazione bra-ket di Dirac, vengono enunciati i postulati alla base della teoria quantistica. In seguito si affronta l'analisi delle due esperienze a cui Ekert fa riferimento nel suo articolo, la versione di Bohm del paradosso EPR e la derivazione della disuguaglianza di Bell proposta dagli studiosi Clauser, Horne, Shimony e Holt. Infine si procede alla descrizione del protocollo di Ekert, analizzandone il funzionamento sia da un punto di vista teorico sia pratico, mettendo in luce i riferimenti alla teoria quantistica e in particolare alla disuguaglianza di Bell. Viene posta attenzione al caso della presenza di Eva, facendo notare come in questo caso la disuguaglianza di Bell sia soddisfatta. Inoltre viene analizzato un secondo protocollo basato su EPR e vengono chiarite le differenze rispetto al primo. In conclusione, vengono descritti i pro e i contro dell'utilizzo di tale protocollo, la possibilità di implementazioni pratiche e l'importanza della crittografia quantistica in generale.
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Le, Quoc Cuong. "Autour des réseaux quantiques et des modèles de relais pour la clé quantique." Phd thesis, Télécom ParisTech, 2009. http://pastel.archives-ouvertes.fr/pastel-00006239.
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La distribution de clé quantique (QKD - Quantum Key Distribution) est une technologie permettant d'assurer au niveau théorique l'inviolabilité des clés transmises. Cependant, certains problèmes d'ordre pratique de mise en œuvre restent ouverts, en particulier, concernant l'augmentation de la portée d'application de QKD. L'objectif de la thèse est de répondre aux deux questions colérées suivantes : (1) comment de construire des réseaux QKD de grande taille; (2) comment sécuriser les relais des clés QKD. Nous avons proposé, dans un premier temps, un modèle permettant de garantir la sécurité de la transmission de clés dans un réseau QKD de grande taille en utilisant un routage stochastique. L'efficacité de ce procédé est démontrée à l'aide de la théorie de la percolation. Dans un deuxième temps, nous avons exploré la sécurité des modèles de relais des clés QKD et arrivons à proposer quatres nouveaux modèles capables à étendre la portée de QKD.
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Avveduti, Silvia. "Analysis of multi-hop Teleportation Protocols for Quantum Networks." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2020. http://amslaurea.unibo.it/19934/.
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Quantum mechanics for computation and information purposes has seen a burst of interest in the scientific community and companies, due to the potential unique computational power offered by quantum computers, not achievable through classical computers. In particular two technologies are used in most quantum computers, which are the trapped ions and artificial atoms, but many different technologies are currently being studied for the physical implementation of quantum information systems. Quantum computers are challenging to build, because the element which represents information, the qubit, requires strict conditions such as isolation from the environment and a very refined control. Moreover, qubits cannot intrinsically reject noise as classical bits do. This thesis is organized as follows. In Chapter 2 the essential concepts for Quantum Computation and Information are introduced; in Chapter 3 an overview of the main applications is displayed; in Chapter 4 the current results in entanglement and teleportation in Quantum Network protocols are shown. The experimental outcomes obtained in IBM Q are discussed in Chapter 5. Finally, Chapter 6 contains the conclusions.
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Qu, Zhen, and Ivan B. Djordjevic. "High-speed continuous-variable quantum key distribution over atmospheric turbulent channels." SPIE-INT SOC OPTICAL ENGINEERING, 2017. http://hdl.handle.net/10150/626486.
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We experimentally demonstrate a RF-assisted four-state continuous-variable quantum key distribution (CV-QKD) system in the presence of turbulence. The atmospheric turbulence channel is emulated by two spatial light modulators (SLMs) on which two randomly generated azimuthal phase patterns are recorded yielding Andrews' azimuthal phase spectrum. Frequency and phase locking are not required in our system thanks to the proposed digital phase noise cancellation (PNC) stage. Besides, the transmittance fluctuation can be monitored accurately by the DC level in this PNC stage, which is free of post-processing noise. The mean excess noise is measured to be 0.014, and the maximum secret key rate of >20Mbit/s can be obtained with the transmittance of 0.85, while employing the commercial PIN photodetectors.
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Cusini, Gabriele. "Quantum Key Distribution with Continuous Variables for Satellite Systems." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2019.
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Recenti studi hanno dimostrato come i più avanzati algoritmi per la generazione e scambio di chiavi crittografiche risultino insicuri contro la futura enorme capacità computazionale dei computer quantistici.
Come è possibile ottenere una chiave completamente sicura, assumendo che i computer quantistici possano rendere i protocolli attuali insicuri?
Una possibile soluzione consiste nell'impiego di protocolli come il Quantum Key Distribution (QKD) il quale usa un sistema di comunicazione quantistica per lo scambio della chiave. Tale sistema garantisce la segretezza della chiave in virtù delle proprietà quantistiche di entanglement e quella di sovrapposizione di stati quantistici.
Nelle comunicazioni quantistiche esistono due principali modi per mappare le informazioni, il primo consiste nel considerare stati quantici discreti 'Discrete Variable quantum state' (DV) mentre il secondo li considera continui 'Continuous Variable quantum state' (CV). E' su questa ultima rappresentazione che si basa il protocollo QKD analizzato e in fine simulato in questo elaborato.
La trattazione del protocollo CV QKD verrà svolta considerando uno scenario di comunicazione terra-satellite in quanto esso rappresenta un importante passo verso un sistema quantistico globale, non limitato dai problemi di distanze propri delle fibre ottiche o dei canali terrestri.
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Rödiger, Jasper. "Time-Frequency Quantum Key Distribution: Numerical Assessment and Implementation over a Free-Space Link." Doctoral thesis, Humboldt-Universität zu Berlin, 2020. http://dx.doi.org/10.18452/21046.
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Die Quantenschlüsselverteilung (QKD), die erste anwendbare Quantentechnologie, verspricht informationstheoretisch sichere Kommunikation. In der vorliegenden Arbeit wurde das Zeit-Frequenz (TF)-QKD-Protokoll untersucht, das Zeit und Frequenz, nämlich Puls-Positionsmodulation (PPM) im Zeitbereich und Frequenzumtastung (FSK) im Frequenzbereich als die beiden komplementären Basen verwendet. Seine Sicherheit beruht den Quanteneigenschaften von Licht und auf der Zeit-Frequenz-Unschärferelation.
TF-QKD kann mit größtenteils Standard-Telekommunikationstechnologie im 1550-nm-Band implementiert werden. Die PPM-Basis kann mit Modulatoren und die FSK-Basis mit Hilfe der Wellenlängenmultiplex-Technologie realisiert werden. Das TF-QKD-Protokoll ist in der Lage, ein beliebig großes Alphabet bereitzustellen, was mehr als 1 bit/Photon ermöglicht. Darüber hinaus ist es robust gegenüber athmosphärischen Störungen und somit für die Übertragung über den Freiraumkanal geeignet.
In der vorliegenden Arbeit wird das TF-QKD-Protokoll theoretisch bewertet, mit Standardkomponenten für 1 bit/Photon implementiert und die Freiraumübertragung mit optischem Tracking über eine 388 m Teststrecke wird bei Tageslicht demonstriert. Unter Verwendung der vorhandenen Komponenten konnte eine sichere Schlüsselrate von 364 kbit/s back-to-back und 9 kbit/s über den Freiraumkanal demonstriert werden.Quantum key distribution (QKD), the first applicable quantum technology, promises information theoretically secure communication. In the presented work the time-frequency (TF)-QKD protocol was examined, which uses time and frequency, namely pulse position modulation (PPM) in the time domain and frequency shift keying (FSK) in the frequency domain as the two complementary bases. Its security relies on the quantum properties of light and the time-frequency uncertainty relation. TF-QKD can be implemented mostly with standard telecom-technology in the 1550 nm band. The PPM basis can be implemented with modulators and the FSK basis with help of wavelength-division multiplexing technology. The TF-QKD protocol is capable of providing an arbitrarily large alphabet enabling more than 1 bit/photon. Moreover, it is robust in the atmosphere making it suitable for transmission over the free-space channel. In the present work the TF-QKD protocol is assessed theoretically, implemented with off-the-shelf components for 1 bit/photon and free-space transmission with optical tracking over a 388 m testbed is demonstrated in daylight. Using components at hand, secret key rates of 364 kbit/s back-to-back and 9 kbit/s over the free-space channel could be demonstrated.
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Leifgen, Matthias. "Protocols and components for quantum key distribution." Doctoral thesis, Humboldt-Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät, 2016. http://dx.doi.org/10.18452/17473.
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In dieser Doktorarbeit werden zwei Konzepte der Quanteninformationsverarbeitung realisiert. Der Quantenschlüsselaustausch ist revolutionär, weil er perfekte Sicherheit gewährleistet. Zahlreiche Quantenkryptografieprotokolle wurden schon untersucht. Zwei Probleme bestehen. Zum einen ist es sehr schwer, die Bedingungen herzustellen, die in den Annahmen für perfekte Sicherheit impliziert sind. Zum anderen sind die Reichweiten auf momentan etwa 200 km begrenzt, aufgrund des abnehmenden Signals gegenüber des konstanten Rauschens. Ein Experiment dieser Doktorarbeit beschäftigt sich mit dem ersten Problem. Insbesondere der übertragene Quantenzustands ist kritisch für die Sicherheit des Verfahrens. Es werden Einzelphotonen von Stickstoff- Fehlstellen-Zentren und zum ersten Mal von Silizium-Fehlstellen-Zentren für einen Quantenschlüsselaustausch mit Hilfe des BB84-Protokolls benutzt. Die Abweichung von idealen Einzelphotonenzuständen sowie deren Bedeutung für die Sicherheit werden analysiert. Die Übertragung von Quantenzuständen via Satellit könnte das Problem der begrenzten Reichweite lösen. Das neue Frequenz-Zeit- Protokoll eignet sich dafür besonders gut. Es wird während dieser Arbeit zum ersten Mal überhaupt implementiert. Umfangreiche Untersuchungen inklusive der Variation wesentlicher experimenteller Parameter geben Aufschluss über die Leistungsfähigkeit und Sicherheit des Protokolls. Außerdem werden elementare Bestandteile eines vollautomatischen Experiments zum Quantenschlüsselaustausch über Glasfasern in der sogenannten Time-bin-Implementierung mit autonomem Sender und Empfänger realisiert. Ein anderes Konzept der Quanteninformationsverarbeitung ist die Herstellung zufälliger Bitfolgen durch den Quantenzufall. Zufällige Bitfolgen haben zahlreiche Anwendungsgebiete in der Kryptografie und der Informatik. Die Realisierung eines Quantenzufallszahlengenerators mit mathematisch beschreibbarer und getesteter Zufälligkeit und hoher Bitrate wird ebenfalls beschrieben.In this thesis, photonic quantum states are used for experimental realisations of two different concepts of quantum information processing. Quantum key distribution (QKD) is revolutionary because it is the only cryptographic scheme offering unconditional security. Two major problems prevail: Firstly, matching the conditions for unconditional security is challenging, secondly, long distance communication beyond 200 km is very demanding because an increasingly attenuated quantum state starts to fail the competition with constant noise. One experiment accomplished in this thesis is concerned with the first problem. The realisation of the actual quantum state is critical. Single photon states from nitrogen and for the first time also silicon vacancy defect centres are used for a QKD transmission under the BB84 (Bennett and Brassard 1984). The deviation of the used single photon states from the ideal state is thoroughly investigated and the information an eavesdropper obtains due to this deviation is analysed. Transmitting quantum states via satellites is a potential solution to the limited achievable distances in QKD. A novel protocol particularly suited for this is implemented for the first time in this thesis, the frequency-time (FT) protocol. The protocol is thoroughly investigated by varying the experimental parameters over a wide range and by evaluating the impact on the performance and the security. Finally, big steps towards a fully automated fibre-based BB84 QKD experiment in the time-bin implementation with autonomous sender and receiver units are accomplished. Another important concept using quantum mechanical properties as a resource is a quantum random number generator (QRNG). Random numbers are used for various applications in computing and cryptography. A QRNG supplying bits with high and quantifiable randomness at a record-breaking rate is reported and the statistical properties of the random output is thoroughly tested.
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Bogdanski, Jan. "Experimental multiuser secure quantum communications." Doctoral thesis, Stockholms universitet, Fysikum, 2009. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-26498.
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We are currently experiencing a rapid development of quantum information, a new branch of science, being an interdisciplinary of quantum physics, information theory, telecommunications, computer science, and many others. This new science branch was born in the middle of the eighties, developed rapidly during the nineties, and in the current decade has brought a technological breakthrough in creating secure quantum key distribution (QKD), quantum secret sharing, and exciting promises in diverse technological fields. Recent QKD experiments have achieved high rate QKD at 200 km distance in optical fiber. Significant QKD results have also been achieved in free-space. Due to the rapid broadband access deployment in many industrialized countries and the standing increasing transmission security treats, the natural development awaiting quantum communications, being a part of quantum information, is its migration into commercial switched telecom networks. Such a migration concerns both multiuser quantum key distribution and multiparty quantum secret sharing that have been the main goal of my PhD studies. They are also the main concern of the thesis. Our research efforts in multiuser QKD has led to a development of the five-user setup for transmissions over switched fiber networks in a star and in a tree configuration. We have achieved longer secure quantum information distances and implemented more nodes than other multi-user QKD experiments. The measurements have shown feasibility of multiuser QKD over switched fiber networks, using standard fiber telecom components. Since circular architecture networks are important parts of both intranets and the Internet, Sagnac QKD has also been a subject of our research efforts. The published experiments in this area have been very few and results were not encouraging, mainly due to the single mode fiber (SMF) birefringence. Our research has led to a development of a computer controlled birefringence compensation in Sagnac that open the door to both classical and quantum Sagnac applications. On the quantum secret sharing side, we have achieved the first quantum secret sharing experiment over telecom fiber in a five-party implementation using the "plug & play" setup and in a four-party implementation using Sagnac configuration. The setup measurements have shown feasibility and scalability of multiparty quantum communication over commercial telecom fiber networks.
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Kaiser, 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.
Full textAbstract:
Le but de cette thèse est de développer des sources d'intrication photonique pour étudier les réseaux de communication quantique et l'optique quantique fondamentale. Trois sources très performantes sont construites uniquement autour de composants standards de l'optique intégrée et des télécommunications optiques. La première source génère de l'intrication en polarisation via une séparation deterministe des paires de photons dans deux canaux adjacents des télécommunications. Cette source est donc naturellement adaptée à la cryptographie quantique dans les réseaux à multiplexage en longueurs d'ondes. La seconde source génère, pour la première fois, de l'intrication en time-bins croisés, autorisant l'implémentation de crypto-systèmes quantiques à base d'analyseurs passifs uniquement. La troisième source génère, avec une efficacité record, de l'intrication en polarisation via un convertisseur d'observable temps/polarisation. La bande spectrale des photons peut être choisie sur plus de cinq ordres de grandeur (25 MHz - 4 THz), rendant la source compatible avec toute une variété d'applications avancées, telles que la cryptographie, les relais et les mémoires quantiques. Par ailleurs, cette source est utilisée pour revisiter la notion de Bohr sur la complémentarité des photons uniques en employant un interféromètre de Mach-Zehnder dont la lame s ́eparatrice de sortie se trouve dans une superposition quantique d'être à la fois présente et absente. Enfin, pour adapter la longueur d'onde des paires des photons télécoms intriqués vers les longueurs d'ondes d'absorption des mémoires quantiques actuelles, un convertisseur cohérent de longueur d'onde est présenté et discuté.
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Schröder, Tim. "Integrated photonic systems for single photon generation and quantum applications." Doctoral thesis, Humboldt-Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät I, 2013. http://dx.doi.org/10.18452/16723.
Full textAbstract:
Im Rahmen der vorliegenden Dissertation wurden neuartige integrierte Einzelphotonenquellen (EPQ) und ihre Anwendung für die Quanteninformationsverarbeitung entwickelt und untersucht. Die Erzeugung von Einzelphotonen basiert auf einzelnen Defektzentren in nanometergroßen Diamantkristallen mit einzigartigen optischen Eigenschaften: Stabilität bei Zimmertemperatur ohne optisches Blinken. Diamantkristalle mit Größen bis unter 20nm wurden mit neuartigen „pick-and-place“ Techniken (z.B. mit einem Atomkraftmikroskop) in komplexe photonische Strukturen integriert. Zwei unterschiedliche Ansätze für die Realisierung der neuartigen EPQ wurden verfolgt. Beim ersten werden fluoreszierende Diamantkristalle in nano- und mikrometergroße Faser-basierte oder resonante Strukturen in einem „bottom-up“ Ansatz integriert, dadurch werden zusätzliche optische Komponenten überflüssig und das Gesamtsystem ultra-stabil und wartungsfrei. Der zweite Ansatz beruht auf einem Festkörperimmersionsmikroskop (FIM). Seine Festkörperimmersionslinse wirkt wie eine dielektrische Antenne für die Emission der Defektzentren. Es ermöglicht die höchsten bisher erreichten Photonenzählraten von Stickstoff-Fehlstellen von bis zu 2.4Mcts/s und Einsammeleffizienzen von bis zu 4.2%. Durch Anwendung des FIM bei cryogenen Temperaturen wurden neuartige Anwendungen und fundamentale Untersuchungen möglich, weil Photonenraten signifikant erhöht wurden. Die Bestimmung der spektralen Diffusionszeit eines einzelnen Defektzentrums (2.2µs) gab neue Erkenntnisse über die Ursachen von spektraler Diffusion. Spektrale Diffusion ist eine limitierende Eigenschaft für die Realisierung von Quanteninformationsanwendungen. Das Tisch-basierte FIM wurde außerdem als kompakte mobile EPQ mit Ausmaßen von nur 7x19x23cm^3 realisiert. Es wurde für ein Quantenkryptographie-Experiment implementiert, zum ersten Mal mit Siliziumdefektzentren. Des Weiteren wurde ein neues Konzept für die Erzeugung von infraroten EPQ entwickelt und realisiert.The presented thesis covers the development and investigation of novel integrated single photon (SP) sources and their application for quantum information schemes. SP generation was based on single defect centers in diamond nanocrystals. Such defect centers offer unique optical properties as they are room temperature stable, non-blinking, and do not photo-bleach over time. The fluorescent nanocrystals are mechanically stable, their size down to 20nm enabled the development of novel nano-manipulation pick-and-place techniques, e.g., with an atomic force microscope, for integration into photonic structures. Two different approaches were pursued to realize novel SP sources. First, fluorescent diamond nanocrystals were integrated into nano- and micrometer scaled fiber devices and resonators, making them ultra-stable and maintenance free. Secondly, a solid immersion microscope (SIM) was developed. Its solid immersion lens acts as a dielectric antenna for the emission of defect centers, enabling the highest photon rates of up to 2.4Mcts/s and collection efficiencies of up to 4.2% from nitrogen vacancy defect centers achieved to date. Implementation of the SIM at cryogenic temperatures enabled novel applications and fundamental investigations due to increased photon rates. The determination of the spectral diffusion time of a single nitrogen vacancy defect center (2.2µs) gave new insights about the mechanisms causing spectral diffusion. Spectral diffusion is a limiting property for quantum information applications. The table-top SIM was integrated into a compact mobile SP system with dimension of only 7x19x23cm^3 while still maintaining record-high stable SP rates. This makes it interesting for various SP applications. First, a quantum key distribution scheme based on the BB84 protocol was implemented, for the first time also with silicon vacancy defect centers. Secondly, a conceptually novel scheme for the generation of infrared SPs was introduced and realized.
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Lin, Yao-Ting, and 林耀廷. "A Study on the Twin-Field QKD Protocol." Thesis, 2019. http://ndltd.ncl.edu.tw/handle/7t2ezh.
Full textAbstract:
碩士國立臺灣大學
物理學研究所
107
Recently, a new protocol, the twin-field QKD (TFQKD) protocol, has been proposed and is claimed to overcome the fundamental limits of quantum repeater-less communications. Soon after its appearance, the related research has gained lot of focus. In this thesis, we first review the existing protocol and make a comparison between them and the TFQKD protocol. Furthermore, we classify recent papers related to the TFQKD protocols into two main types: the phase-matching-type (PM) protocol and the sending-or-not-sending-type (SNS) protocol. We review the arguments for the security and simulate the key rate versus distance for both types of protocols under different conditions. Then we compare their performances between the two types of protocols. To investigate the feasibility for practical implementation, we also discuss the finite-size effect for the post-processing block size. The results show both protocols are capable of overcoming the repeater-less bound with current devices and technology.
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Hsieh, Yi-Chia, and 謝易家. "Dark Counts Suppression Based on Balanced Dual-APD Scheme and for QKD System." Thesis, 2012. http://ndltd.ncl.edu.tw/handle/z48zpe.
Full textAbstract:
碩士國立臺北科技大學
光電工程系研究所
100
In this thesis, dark counts suppression and detection frequency improvement by using a balanced dual avalanche photodiode scheme was proposed. In order to apply this experimental setup to the quantum key distribution (QKD) system, we discuss and analyze the characteristic parameters of the used APD, including dark count probability (DCP), single photon detection efficiency (SPDE), noise equipment power (NEP), detection frequency and quantum bit error rate (QBER). The signal from the single photon detection was feed into the self-differencing circuit which can reduce the spiking noise. In accordance with self-differencing circuit requirements, we choose the amplifier with a large slew rate for achieving low dark count probability and higher detection frequency. We are also constructed a simple QKD system at the same time. The system would be has best quantum bit error rate (QBER) under -50℃ and 1 MHz、2 MHz. In this study, we surveyed the influence of different parameters, such as temperature, excess bias voltage and pulse width. To demonstrate the afterpulsing effect by releasing the trapped carriers at lower temperature and high detection frequency, the APD was cooled down to a temperature of -60℃ and raised the frequency to 10 MHz. And then we calculated the optimum QBER and transmission distance from the obtained date of the best detection parameter in theory. Finally, at a temperature of -50℃ and detection frequency of 1 MHz, the excess bias voltage of 2.0 V was applied on balanced dual avalanche photodiode schematic to characterize single-photon performance. The best single photon detection efficiency of 11.6% at dark count probability 9.26×10-4 and noise equipment power as low as 1.06×10-15 W/Hz1/2 are obtained. Based on the above conditions, the calculated corresponding QBER values of back to back and after 10.5 km fiber length are 7% and 10.65%. The maximum available transmission distance was 22 km as the QBER below 15%. However, after actual transmission through optical fiber of 10.5 km the obtained QBER was 14.47%. The difference of QBER between the actual transmission value and the calculated value was 3.82 percent.
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Ma, Xiongfeng. "Quantum Cryptography: From Theory to Practice." Thesis, 2008. http://hdl.handle.net/1807/17302.
Full textAbstract:
Quantum cryptography or quantum key distribution (QKD) applies fundamental laws of quantum physics to guarantee secure communication. The security of quantum cryptography was proven in the last decade. Many security analyses are based on the assumption that QKD system components are idealized. In practice, inevitable device imperfections may compromise security unless these imperfections are well investigated.
A highly attenuated laser pulse which gives a weak coherent state is widely used in QKD experiments. A weak coherent state has multi-photon components, which opens up a security loophole to the sophisticated eavesdropper. With a small adjustment of the hardware, we will prove that the decoy state method can close this loophole and substantially improve the QKD performance. We also propose a few practical decoy state protocols, study statistical fluctuations and perform experimental demonstrations. Moreover, we will apply the methods from entanglement distillation protocols based on two-way classical communication to improve the decoy state QKD performance. Furthermore, we study the decoy state methods for other single photon sources, such as triggering parametric down-conversion (PDC) source. Note that our work, decoy state protocol, has attracted a lot of scientific and media interest. The decoy state QKD becomes a standard technique for prepare-and-measure QKD schemes.
Aside from single-photon-based QKD schemes, there is another type of scheme based on entangled photon sources. A PDC source is commonly used as an entangled photon source. We propose a model and post-processing scheme for the entanglement-based QKD with a PDC source. Although the model is proposed to study the entanglement-based QKD, we emphasize that our generic model may also be useful for other non-QKD experiments involving a PDC source. By simulating a real PDC experiment, we show that the entanglement-based QKD can achieve longer maximal secure distance than the single-photon-based QKD schemes.
We propose a time-shift attack that exploits the efficiency mismatch of two single photon detectors in a QKD system. This eavesdropping strategy can be realized by current technology. We will also discuss counter measures against the attack and study the security of a QKD system with efficiency mismatch detectors.
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Gigov, Nikolay. "Quantum Key Distribution Data Post-Processing with Limited Resources: Towards Satellite-Based Quantum Communication." Thesis, 2013. http://hdl.handle.net/10012/7244.
Full textAbstract:
Quantum key distribution (QKD), a novel cryptographic technique for secure distribution of secret keys between two parties, is the first successful quantum technology to emerge from quantum information science. The security of QKD is guaranteed by fundamental properties of quantum mechanical systems, unlike public-key cryptography whose security depends on difficult to solve mathematical problems such as factoring. Current terrestrial quantum links are limited to about 250 km. However, QKD could soon be deployed on a global scale over free-space links to an orbiting satellite used as a trusted node.
Envisioning a photonic uplink to a quantum receiver positioned on a low Earth orbit satellite, the Canadian Quantum Encryption and Science Satellite (QEYSSat) is a collaborative project involving Canadian universities, the Canadian Space Agency (CSA) and industry partners. This thesis presents some of the research conducted towards feasibility studies of the QEYSSat mission.
One of the main goals of this research is to develop technologies for data acquisition and processing required for a satellite-based QKD system. A working testbed system helps to establish firmly grounded estimates of the overall complexity, the computing resources necessary, and the bandwidth requirements of the classical communication channel. It can also serve as a good foundation for the design and development of a future payload computer onboard QEYSSat.
This thesis describes the design and implementation of a QKD post-processing system which aims to minimize the computing requirements at one side of the link, unlike most traditional implementations which assume symmetric computing resources at each end. The post-processing software features precise coincidence analysis, error correction based on low-density parity-check codes, privacy amplification employing Toeplitz hash functions, and a procedure for automated polarization alignment.
The system's hardware and software components integrate fully with a quantum optical apparatus used to demonstrate the feasibility of QKD with a satellite uplink. Detailed computing resource requirements and QKD results from the operation of the entire system at high-loss regimes are presented here.
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Erven, Chris. "On Free Space Quantum Key Distribution and its Implementation with a Polarization-Entangled Parametric Down Conversion Source." Thesis, 2007. http://hdl.handle.net/10012/3021.
Full textAbstract:
This thesis describes the deployment of a free-space quantum key
distribution system across the University of Waterloo campus. The
quantum key distribution system has the ability to provide
unconditionally secure communication between two parties: Alice and
Bob. The system exploits the quantum mechanical property of
entanglement in order to generate a key. Security is then guaranteed
by the No-Cloning theorem and the laws of quantum mechanics which
prevent a quantum system from being measured without disturbing it.
Polarization-entangled photon pairs are created using the non-linear
optical process of type-II spontaneous parametric down-conversion. A
free-space link of approximately $\mathrm{580~m}$ is used to
distribute one-half of the pairs to Alice at a distant location,
while the other half of the pairs are locally detected by Bob. The
details of the detection apparatus necessary to measure the
polarization of the photons and the software used to process the
measurement data according to the BBM92 protocol are described. An
experimental violation of the CHSH inequality (a derivative of the
original Bell inequality) is demonstrated to show that
polarization-entangled photon pairs are in fact being distributed to
the two parties. Finally, the full BBM92 protocol is performed using
the entangled photon pairs to generate a secure key and transmit an
encrypted message between Alice and Bob. Currently, the system can
only be operated at night because background light saturates the
detectors during the day; however, future work will focus on making
daylight operation feasible.
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Meyer-Scott, Evan. "Experimental quantum communication in demanding regimes." Thesis, 2011. http://hdl.handle.net/10012/6052.
Full textAbstract:
Quantum communication promises to outperform its classical counterparts and enable protocols previously impossible. Specifically, quantum key distribution (QKD) allows a cryptographic key to be shared between distant parties with provable security. Much work has been performed on theoretical and experi- mental aspects of QKD, and the push is on to make it commercially viable and integrable with existing technologies. To this end I have performed simulations and experiments on QKD and other quantum protocols in regimes previously unexplored.
The first experiment involves QKD via distributed entanglement through the standard telecommunications optical fibre network. I show that entanglement is preserved, even when the photons used are a shorter wavelength than the design of the optical fibre calls for. This surprising result is then used to demonstrate QKD over installed optical fibre, even with co-propagating classical traffic. Because the quantum and classical signals are sufficiently separated in wavelength, little cross-talk is observed, leading to high compatibility between this type of QKD and existing telecommunications infrastructure.
Secondly, I demonstrate the key components of fully-modulated decoy-state QKD over the highest-loss channel to date, using a novel photon source based on weak coherent (laser) pulses. This system has application in a satellite uplink of QKD, which would enable worldwide secure communication. The uplink allows the complex quantum source to be kept on the ground while only simple receivers are in space, but suffers from high link loss due to atmospheric turbulence, necessitating the use of specific photon detectors and highly tailored photon pulses. My results could be applied in a near term satellite mission.