Dissertations / Theses on the topic 'Entanglement'
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Gühne, Otfried. "Detecting quantum entanglement entanglement witnesses and uncertainty relations /." [S.l. : s.n.], 2004. http://deposit.ddb.de/cgi-bin/dokserv?idn=972550216.
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Uyanik, Kivanc. "Entanglement Measures." Master's thesis, METU, 2008. http://etd.lib.metu.edu.tr/upload/12609292/index.pdf.
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Being a puzzling feature of quantum mechanics, entanglement caused many debates since the infancy days of quantum theory. But it is the last two decades that it has started to be seen
as a resource for physical tasks which are not possible or extremely infeasible to be done classically. Popular examples are quantum cryptography - secure communication based on
laws of physics - and quantum computation - an exponential speedup for factoring large integers. On the other hand, with current technological restrictions it seems to be difficult to preserve specific entangled states and to distribute them among distant parties. Therefore a precise measurement of quantum entanglement is necessary. In this thesis, common bipartite
and multipartite entanglement measures in the literature are reviewed. Mathematical definitions, proofs of satisfaction of basic axioms and significant properties for each are given as
far as possible. For Tangle and Geometric Measure of Entanglement, which is a multipartite measure, results of numerical calculations for some specific states are shown.
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Kintas, Seckin. "Entanglement Transformations." Master's thesis, METU, 2009. http://etd.lib.metu.edu.tr/upload/3/12611363/index.pdf.
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Entanglement is a special correlation of the quantum states of two or more particles. It is also a useful resource enabling us to complete tasks that cannot be done by classical means. As a result, the transformation of entangled states of distant particles by local means arose as an important problem in quantum information theory. In this thesis, we first review some of the studies done on the entanglement transformations. We also develop the necessary and sufficient conditions for the deterministic transformation of W-type states.
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Fina, Damiano <1990>. "Fictionalizing Entanglement." Master's Degree Thesis, Università Ca' Foscari Venezia, 2015. http://hdl.handle.net/10579/6038.
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Nelle esperienze narrative immersive e transmediali offerte dal cinema contemporaneo viene a delinearsi un ruolo sempre più performativo da parte degli ormai “ex” spettatori. Apparentemente, al fruitore-medio non verrebbe tanto chiesto uno sforzo interpretativo, quanto piuttosto di transitare all’interno di percorsi pre-impostati in un vasto “parco giochi” che funzionerebbe come stimolatore di sensi. Secondo il presente lavoro risulta veramente riduttivo condannare a priori questa tendenza fruitiva alla noncuranza delle interpretazioni e della ricerca dei significati, piuttosto sarebbe utile indagare la natura delle narrazioni di volta in volta costruite e in particolare analizzare il portato delle emozioni sollevate rispetto agli abiti fruitivi messi in gioco. Un approccio all’esperienza e alla teoria delle emozioni come quello deweyano risulterebbe particolarmente fertile per approfondire questa analisi. A partire da questa matrice filosofica deweyana e dall’analisi della recente letteratura sul fictionalizing -da Wolfgang Iser all’evoluzionismo estetico di Brian Boyd e Denis Dutton- s’indagherà il contributo delle narrazioni nell’innovazione dei processi di produzione e fruizione nell’industria culturale, evidenziando di conseguenza le ricadute originate o potenzialmente generabili e, soprattutto, discriminandone gli esiti con l’esemplificazione dei casi analizzati: il cinema contemporaneo alla luce del transmedia storytelling e un focus sulla serie TV Supernatural.
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Volz, Jürgen. "Atom-Photon Entanglement." Diss., lmu, 2006. http://nbn-resolving.de/urn:nbn:de:bvb:19-56356.
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Wieczorek, Witlef. "Multi-Photon Entanglement." Diss., lmu, 2009. http://nbn-resolving.de/urn:nbn:de:bvb:19-110383.
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Xiong, Han. "Coherence-induced entanglement." Texas A&M University, 2005. http://hdl.handle.net/1969.1/3797.
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Coherence and entanglement are the two key concepts that distinguish quantum
mechanics from classical mechanics. Many novel phenomena occuring in the quantum
world are due to these two Âphysical quantitiesÂ. They also play essential roles in
quantum computation and quantum information. For example, coherence, which
says that a quantum mechanical system could be in a superposition state, makes the
quantum parallel computing scheme possible; and entanglement, which says that two
quantum systems separated in space could be in an intervened state, is the key factor
in various quantum teleportation algorithms.
We have studied entanglement generation in various systems. We found that with
atomic coherence, entanglement could be generated between two thermal fields with
arbitrarily high temperatures. We also found that temperature difference instead of
the purity of state is essential for the entanglement generation between an atom and
a thermal field. We discovered that correlated spontaneous emission lasers (CELs)
could be used to generate bright entanglement laser beams. As a special case of CEL
systems, we studied entanglement generation in Non-degenerate Optical Parametric
Amplifiers (NOPAs). We performed the input-output calculations for a NOPA system
and showed that the two output optical beams are still entangled. This justifies our idea that CEL (or NOPA) systems can be used as an ideal entanglement source
for various quantum information schemes. From an experimental point of view, we
considered the effects of pumping fluctuations on entanglement generation in CEL
and NOPA systems. We found that these fluctuations, especially the phase diffusion
processes, in the pump laser would greatly reduce the entanglement generated in such
systems.
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Spekkens, Robert W. "Aspects of entanglement." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2001. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp04/NQ63757.pdf.
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Ray, Megan. "Verifying Optical Entanglement." Thesis, University of Oregon, 2013. http://hdl.handle.net/1794/13430.
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We look at the problem of verifying optical entanglement for two types of states relevant to quantum information processing. One type occurs in Hong-Ou-Mandel interference and is relevant to quantum computing. The other type is time frequency entanglement which is useful for quantum key distribution. For these types of states the conventional methods of entanglement verification do not work well, and we develop new criteria and methods to verify entanglement of such states. Explicitly, one method takes into account the possible multimode character of two photons, while the other method takes into account the missing data that occur due to the finite range of detectors.
This dissertation includes previously published and unpublished co-authored material.
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McDermott, Michael. "Momentum-space entanglement and the gravity of entanglement in AdS/CFT." Thesis, University of British Columbia, 2014. http://hdl.handle.net/2429/50312.
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In the first part of this thesis we explore the entanglement structure of relativistic field theories in momentum space. We discuss a Wilsonian path integral formulation and a perturbative approach. Using perturbation theory we obtain results for specific quantum field theories. These are understood through scaling and decoupling properties of field theories. Convergence of the perturbation theory taking loop diagrams into account is also discussed. We then discuss the entanglement structure in systems where Lorentz invariance is broken by a Fermi surface. The Fermi surface helps the convergence of perturbation theory and entanglement of modes near the Fermi surface is shown to be amplified, even in the presence of a large momentum cutoff.
In the second part of this thesis we explore the connection between entanglement and gravity in the context of the AdS/CFT correspondence. We show that there are certain thermodynamic-like relations common to all conformal field theories, which when mapped via the AdS/CFT correspondence to the bulk are tantamount to Einstein's equations, to lowest order in the metric.Science, Faculty of
Physics and Astronomy, Department of
Graduate
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Clarisse, Lieven. "Entanglement distillation : a discourse on bound entanglement in quantum information theory." Thesis, University of York, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.434001.
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Bae, Joonwoo. "Entanglement and Quantum Cryphtography." Doctoral thesis, Universitat de Barcelona, 2007. http://hdl.handle.net/10803/1589.
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Quantum cryptography is one of the most important quantum information applications. The present thesis covers several topics on quantum cryptography, such as the security analysis of quantum channels for key distribution protocols and the study of quantum cloning.First, we introduce a general formalism to characterize the cryptographic properties of quantum channels in the realistic scenario where the two honest parties employ prepare and measure protocols and the known two-way communication reconciliation techniques. We derive a necessary and sufficient condition to distill a secret key using this type of schemes for arbitrary bipartite quantum systems of finite dimension. The obtained results suggest that there may exist weakly entangling channels useless for key distribution using prepare and measure schemes.
Next, we consider Gaussian states and Gaussian operations for cryptographic tasks and derive a new security condition. As it happens for quantum systems of finite dimension, our results suggest that there may also exist weakly entangled Gaussian states useless for key distribution, using Gaussian operations.
Finally, we study the connection between cloning and state estimation.
It was a long-standing problem to show whether state estimation becomes equivalent to quantum cloning in the asymptotic limit of an infinite number of clones. The equivalence is proven here using two known results in quantum information theory, the monogamy of quantum states and the properties of entanglement-breaking channels.
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Kiesel, Nikolai. "Experiments on Multiphoton Entanglement." Diss., lmu, 2007. http://nbn-resolving.de/urn:nbn:de:bvb:19-77291.
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Hofmann, Julian. "Heralded atom-atom entanglement." Diss., Ludwig-Maximilians-Universität München, 2014. http://nbn-resolving.de/urn:nbn:de:bvb:19-164847.
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Bose, Sougato. "Entanglement manipulations and applications." Thesis, Imperial College London, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.322037.
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Durkin, Gabriel Andrew. "Light & spin entanglement." Thesis, University of Oxford, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.413080.
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Romero, Mary Jacquiline Romero. "Orbital angular momentum entanglement." Thesis, University of Glasgow, 2012. http://theses.gla.ac.uk/3812/.
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Entanglement in higher dimensions is an attractive concept that is a chal- lenge to realise experimentally. To this end, the entanglement of the orbital angular momentum (OAM) of photons holds promise. The OAM state-space is discrete and theoretically unbounded. In the work that follows, we investi- gate various aspects of OAM entanglement. We show how the correlations in OAM and its conjugate variable, angular position, are determined by phase- matching and the shape of the pump beam in spontaneous parametric down- conversion. We implement tests of quantum mechanics which have been previously done for other variables. We show the Einstein-Podolsky-Rosen paradox for OAM and angle, supporting the incompatibility of quantum me- chanics with locality and realism. We demonstrate violations of Bell-type inequalities, thereby discounting local hidden variables for describing the correlations we observe. We show the Hardy paradox using OAM, again highlighting the nonlocal nature of quantum mechanics. We demonstrate violations of Leggett-type inequalities, thereby discounting nonlocal hidden variables for describing correlations. Lastly, we have looked into the entan- glement of topological vortex structures formed from a special superposition of OAM modes and show violations of Bell-type inequalities confined to a finite, isolated volume.
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Gray, Sean. "Quantum Entanglement and Cryptography." Thesis, Uppsala universitet, Teoretisk fysik, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-227085.
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In this paper the features of quantum systems which lay the foundation of quantum entanglement are studied. General properties of entangled states are discussed, including their entropy and relation to Bell's inequality. Applications of entanglement, namely quantum teleportation and quantum cryptography, are also considered.
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Carteret, Hilary Ann. "Symmetry and multiparticle entanglement." Thesis, University of York, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.341118.
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Broadfoot, Stuart Graham. "Long distance entanglement distribution." Thesis, University of Oxford, 2013. http://ora.ox.ac.uk/objects/uuid:e7039911-f16b-4f49-8aab-8bb30ae97daa.
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Developments in the interdisciplinary field of quantum information open up previously impossible abilities in the realms of information processing and communication. Quantum entanglement has emerged as one property of quantum systems that acts as a resource for quantum information processing and, in particular, enables teleportation and secure cryptography. Therefore, the creation of entangled resources is of key importance for the application of these technologies. Despite a great deal of research the efficient creation of entanglement over long distances is limited by inevitable noise. This problem can be overcome by creating entanglement between nodes in a network and then performing operations to distribute the entanglement over a long distance. This thesis contributes to the field of entanglement distribution within such quantum networks. Entanglement distribution has been extensively studied for one-dimensional networks resulting in "quantum repeater" protocols. However, little work has been done on higher dimensional networks. In these networks a fundamentally different scaling, called "long distance entanglement distribution", can appear between the resources and the distance separating the systems to be entangled. I reveal protocols that enable long distance entanglement distribution for quantum networks composed of mixed state and give a few limitations to the capabilities of entanglement distribution. To aid in the implementation of all entanglement distribution protocols I finish by introducing a new system, composed of an optical nanofibre coupled to a carbon nanotube, that may enable new forms of photo-detectors and quantum memories.
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Berthiere, Clément. "Entanglement, boundaries and holography." Thesis, Tours, 2017. http://www.theses.fr/2017TOUR4017.
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La notion d’entropie d’intrication a eu un profond impact sur la physique théorique, particulièrement depuis ces dix dernières années. D’abord introduite afin expliquer l’entropie des trous noirs, son champ d’application s’est par la suite ouvert à une grande variété de domaines de recherche, de la matière condensée à la gravitation quantique, de l’information quantique à la théorie quantique des champs. Dans ce contexte scientifique effervescent, l’entropie d’intrication apparait comme un outil central et doit donc intensivement être étudiée. A l’origine de cette thèse se trouve le désir de mieux comprendre cette entropie. D’intéressants développements concernant les effets de bord sur l’entropie d’intrication ont vu le jour récemment. Nous proposons donc d’explorer comment le bord d’un espace affecte l’entropie, en particulier dans la situation où la surface d’intrication intersecte ce bord. Nous présentons des calculs explicites de l’entropie d’intrication en espace plat avec bords. Nous montrons que des termes induits par ces bords apparaissent dans l’entropie et nous soulignons le rôle prépondérant que jouent les conditions aux bords. Nous étudions ensuite la contribution de bord dans le terme logarithmique de l’entropie d’intrication en dimensions trois et quatre. Nous calculons en premier lieu ce terme en théorie des champs pour la théorie N = 4 de Yang-Mills, puis nous répétons ce calcul de manière holographique. Nous montrons que ces deux méthodes de calcul donnent le même résultat, si du côté théorie des champs les conditions aux bords préservent la moitié de la supersymétrie et que du côté gravité l’extension du bord dans le bulk est une surface minimaleThe entanglement entropy has had a tremendous and profound impact on theoretical physics, particularly since the last decade. First introduced in an attempt to explain black holes entropy, it has then found applications in a wide range of research areas, from condensed matter physics to quantum gravity, from quantum information to quantum field theory. In this exciting scientific context, the entanglement entropy has thus emerged as a useful and pivotal tool, and as such justifies the need to be intensively studied. At the heart of this thesis therefore lies the desire to better understand the entanglement entropy. Interesting developments during the recent years concern the boundary effects on the entanglement entropy. This dissertation proposes to explore the question of how the presence of spacetime boundaries affects the entropy, specifically in situations where the entangling surface intersects these boundaries. We present explicit calculations of entanglement entropy in flat spacetime with plane boundaries. We show that boundary induced terms appear in the entropy and we emphasize the prominent role of the boundary conditions. We then study the boundary contribution to the logarithmic term in the entanglement entropy in three and four dimensions. We perform the field theoretic computation of this boundary term for the free N = 4 super-gauge multiplet and then repeat the same calculation holographically. We show that these two calculations are in agreement provided that on the field theory side one chooses the boundary conditions which preserve half of the full supersymmetry and that on the gravity side the extension of the boundary in the bulk is minimal
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Menga, Marina. "Entanglement detection measuring classical correlations." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2017. http://amslaurea.unibo.it/13510/.
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L'entanglement è un fenomeno di natura puramente quantistica ed è considerato la principale risorsa dei protocolli quantistici di manipolazione e trasmissione di informazione.
Lo studio e la caratterizzazione dell'entanglement rivestono dunque un ruolo cruciale nello sviluppo della teoria dell'informazione quantistica e nella comprensione delle strutture fondamentali della meccanica quantistica non relativistica.
Uno dei principali problemi legati alla teoria dell'entanglement è quello di trovare dei criteri ottimali per la rilevazione, la caratterizzazione e la quantificazione dell'entanglement. Ad oggi, non esiste una soluzione completa per questo problema.
In questo lavoro di tesi, abbiamo esaminato e generalizzato un criterio per la rilevazione dell'entanglement basato sulla misura delle correlazioni classiche esistenti tra osservabili locali complementari di un sistema bipartito. In particolare, ci siamo occupati dei criteri che si basano sulla misura dell'informazione mutua, e abbiamo analizzato le prestazioni di questo criterio per una generica coppia di osservabili, non necessariamente complementari. Le prestazioni del nuovo criterio, in termini di efficienza, robustezza ed applicabilità, sono state analizzate in dettaglio per sistemi bipartiti di qubit, poichè in questo caso l'entanglement è completamente caratterizzato e sono a disposizione strumenti di confronto. In particolare, il criterio è stato utilizzato per la rivelazione di entanglement in presenza di rumore esterno e decoerenza.
L'analisi condotta in questa tesi ha mostrato che il criterio presentato è robusto, dal momento che la percentuale di stati rivelati non cala in maniera drammatica quando ci si sposta dalla condizione di complementarietà, e inoltre, pur non avendo performance ottimali rispetto ad altri metodi di rilevazione dell'entanglement, è interessante dal punto di vista applicativo poichè si è rivelato affidabile e complessivamente efficiente.
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De, Fazio Cecilia. "Entanglement Entropy In Excited States." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2018. http://amslaurea.unibo.it/15833/.
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Negli ultimi anni l’entropia di entaglement è stata ampiamente studiata nel campo dell‘integrabilità. Con l‘introduzione del modello a replica è stato possibile portare alla luce le proprietà universali dell’ entropia di entanglement di un sistema bipartito nello stato di vuoto.
In questa tesi si è investigato il problema dell’entropia di entanglement di un sistema bipartito in uno stato eccitato di singola particella. In particolare, si è considerata una teoria bosonica libera in un volume finito, in modo da sfruttare al meglio le tecniche dell‘integrabilità. Nel corso di questa analisi, è stato possibile rielaborare il modello a replica in un volume finito grazie ad un raddoppiamento della teoria bosonica che ha indotto una simmetria U(1) su ogni copia del modello. Tale tecnica, nota in letter- atura come doubling trick ha permesso di ricondurre il calcolo dell’entropia di Renyi a un’opportuna espansione in form factors dei campi U(1) implementanti tale simmetria e valutarne il contributo dominante nel limite in cui il volume è grande.
I risultati ottenuti per la Second Rènyi entropy mostrano che in tale limite, l’eccesso di entanglement dovuto allo stato eccitato rispetto a quello di vuoto è indipendente dall’energia dello stato stesso e può essere interpretato come quantità che misura l’incertezza sulla localizzazione dell’eccitazione nelle due parti di cui è composto il sistema.
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Alsina, Leal Daniel. "Multipartite entanglement and quantum algorithms." Doctoral thesis, Universitat de Barcelona, 2017. http://hdl.handle.net/10803/459120.
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Quantum information science has grown from being a very small subfield in the 70s until being one of the most dynamic fields in physics, both in fundamentals and applications. In the theoretical section, perhaps the feature that has attracted most interest is the notion of entanglement, the ghostly relation between particles that dazzled Einstein and has provided fabulous challenges to build a coherent interpretation of quantum mechanics. While not completely solved, we have today learned enough to feel less uneasy with this fundamental problem, and the focus has shifted towards its potential powerful applications. Entanglement is now being studied from different perspectives as a resource for performing information processing tasks.
With bipartite entanglement being largely understood nowadays, many questions remain unanswered in the multipartite case. The first part of this thesis deals with multipartite entanglement in different contexts. In the first chapters it is studied within the whole corresponding Hilbert space, and we investigate several entanglement measures searching for states that maximize them, including violations of Bell inequalities. Later, focus is shifted towards hamiltonians that have entangled ground states, and we investigate entanglement as a way to establish a distance between theories and we study frustration and methods to efficiently solve hamiltonians that exhibit it.
In the practical section, the most promised upcoming technological advance is the advent of quantum computers. In the 90s some quantum algorithms improving the performance of all known classical algorithms for certain problems started to appear, while in the 2000s the first universal computers of few atoms began to be built, allowing implementation of those algorithms in small scales. The D-Wave machine already performs quantum annealing in thousands of qubits, although some controversy over the true quantumness of its internal workings surrounds it. Many countries in the planet are devoting large amounts of money to this field, with the recent European flagship and the involvement of the largest US technological companies giving reasons for optimism.
The second part of this thesis deals with some aspects of quantum computation, starting with the creation of the field of cloud quantum computation with the appearance of the first computer available to the general public through internet, which we have used and analysed extensively. Also small incursions in quantum adiabatic computation and quantum thermodynamics are present in this second part.La informació quàntica ha crescut des d'un petit subcamp als anys setanta fins a esdevenir un dels camps més dinàmics de la física actualment, tant en aspectes fonamentals com en les seves aplicacions. En la secció teòrica, potser la propietat que ha atret més interès és la noció d'entrellaçament, la relació fantasmagòrica entre partícules que va deixar estupefacte Einstein i que ha suposat un enorme desafiament per a construir una interpretació coherent de la mecànica quàntica. Sense estar totalment solucionat, hem après prou per sentir-nos menys incòmodes amb aquest problema fonamental i el focus s'ha desplaçat a les seves aplicacions potencials. L'entrellaçament s'estudia avui en dia des de diferents perspectives com a recurs per realitzar tasques de processament de la informació. L'entrellaçament bipartit està ja molt ben comprès, però en el cas multipartit queden moltes qüestions obertes. La primera part d'aquesta tesi tracta de l'entrellaçament multipartit en diferents contextos. Estudiem l'hiperdeterminant com a mesura d'entrellaçament el cas de 4 qubits, analitzem l'existència i les propietats matemàtiques dels estats absolutament màximament entrellaçats, trobem noves desigualtats de Bell, estudiem l'espectre d'entrellaçament com a mesura de distància entre teories i estudiem xarxes tensorials per tractar eficientment sistemes frustrats. En l'apartat pràctic, el més prometedor avenç tecnològic del camp és l'adveniment dels ordinadors quàntics. La segona part de la tesi tracta d'alguns aspectes de computació quàntica, començant per la creació del camp de la computació quàntica al núvol, amb l'aparició del primer ordinador disponible per al públic general, que hem usat extensament. També fem petites incursions a la computació quàntica adiabàtica i a la termodinàmica quàntica en aquesta segona part
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Hyllus, Philipp. "Witnessing entanglement in qudit systems." [S.l. : s.n.], 2005. http://deposit.ddb.de/cgi-bin/dokserv?idn=97582161X.
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Tsegaye, Tedros. "Quantum interference, complementarity and entanglement." Doctoral thesis, KTH, Electronic Systems Design, 2000. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-3004.
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Nozaki, Masahiro. "Quantum Entanglement of Local Operators." 京都大学 (Kyoto University), 2015. http://hdl.handle.net/2433/199101.
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Savov, Ivan. "Distributed compression and squashed entanglement." Thesis, McGill University, 2008. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=18745.
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A single quantum state can be shared by many distant parties. In this thesis, we try to characterize the information contents of such distributed states by defining the multiparty information and the multiparty squashed entanglement, two steps toward a general theory of multiparty quantum information. As a further step in that direction, we partially solve the multiparty distributed compression problem where multiple parties use quantum communication to faithfully transfer their shares of a state to a common receiver. We build a protocol for multiparty distributed compression based on the fully quantum Slepian-Wolf protocol and prove both inner and outer bounds on the achievable rate region. We relate our findings to previous results in information theory and discuss some possible applications.Un état quantique peut être partagé entre plusieurs entités qui sont spatialement séparés. Dans ce mémoire, nous essayons de caractériser l'information quantique contenue dans de tels états distribués en définissant et utilisant les notions d'information multipartie (multiparty information) et d'intrication "écrasée" multipartie (multiparty squashed entanglement). Il s'agit de premiers pas vers une théorie générale de l'information quantique multipartie. Nous faisons aussi un autre pas dans cette direction en étudiant le problème de la compression distribuée d'information quantique. En particulier, nous proposons un protocole de compression distribuée basé sur la version quantique du protocole de Slepian et Wolf et analysons ses caractéristiques. Nous discutons aussi la relation entre nos résultats et les travaux précédents dans la théorie de l'information et soulignons quelques applications possibles de notre protocole.
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Vedral, Vlatko. "Quantum information theory of entanglement." Thesis, Imperial College London, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.299786.
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Virmani, Shashank Soyuz. "Entanglement quantification and local discrimination." Thesis, Imperial College London, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.270484.
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Song, David Daegene. "Manipulating quantum information and entanglement." Thesis, University of Oxford, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.365320.
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Henderson, L. "Quantum entanglement and classical information." Thesis, University of Oxford, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.365802.
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Palmer, Timothy Steven. "Modelling a single polymer entanglement." Thesis, University of Reading, 2012. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.559254.
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The slip-spring model introduced by Likhtman (Macromolecules 38, 6128-6139 (2005)) simulates a single chain entangled within a polymer melt. Single-chain models such as the slip-spring model allow the rheology of polymers to be studied without requiring the use of expensive multiple-chain molecular dynamics simulations. This study investigates the slip-spring model in the context of a single entanglement and compares it to a two-chain entanglement model. A better understanding of the mechanisms involved in an entanglement is obtained, through the properties of stress relaxation and mean squared displacement, but also through analysis of the bead positions and bond vectors involved. Flaws are identified within the slip-spring model, for which modifications to the model are suggested, including the addition of a non-isotropic spring-constant and the replacement of the slip-spring by a slip-chain. This examination of the simple case is carried out, so that the knowledge gained may be later applied to the multiple-entanglement slip-spring model. During the course of this study, the generic polymer simulation (GPS) package was con- structed by the Reading Theoretical Polymer Physics Group. GPS provides an object-orientated simulation framework, designed to keep simulations organised and make new simulations faster to create. An overview of the concepts involved is included in this thesis. Another tool encountered within this study is maximum likelihood estimation, a statistical technique that, when applied to polymer models such as the slip-spring model, allows the estimation of model parameters. Such a fitting is not only useful for finding the best parameters, but also prevents the model flaws from being obscured by incorrect parameter fitting.
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Campbell, Earl T. "Distrubuting entanglement for quantum computing." Thesis, University of Oxford, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.504315.
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Tang, Wai Ho. "Quantum Entanglement and Superconducting Qubits." Thesis, Karlstads universitet, Fakulteten för hälsa, natur- och teknikvetenskap (from 2013), 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:kau:diva-32238.
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Conventional computing based on classical technologies is approaching its limits. Therefore scientists are starting to consider the applications of quantum mechanics as a means for constructing more powerful computers. After proposing theoretical methods, many experimental setups have been designed to achieve quantum computing in reality. This thesis gives some background information on the subject of quantum computing. We first review the concept of quantum entanglement, which plays a key role in quantum computing, and then we discuss the physics of the SQUIDs-cavity method proposed by Yang et al., and give the definitions of quantum gates which are the elements that are needed to construct quantum circuits. Finally we give an overview of recent developments of SQUIDs-cavity systems and quantum circuits after Yang et al.'s proposal in 2003. These new developments help to take a step towards the constructions of higher levels of quantum technologies, e.g. quantum algorithms and quantum circuits.
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Lampert, Richart Daniel. "Higher dimensional time-energy entanglement." Diss., Ludwig-Maximilians-Universität München, 2014. http://nbn-resolving.de/urn:nbn:de:bvb:19-171352.
Full textAbstract:
Judging by the compelling number of innovations based on taming quantum mechanical effects, such as the development of transistors and lasers, further research in this field promises to tackle further technological challenges in the years to come. This statement gains even more importance in the information processing scenario. Here, the growing data generation and the correspondingly higher need for more efficient computational resources and secure high bandwidth networks are central problems which need to be tackled. In this sense, the required CPU minituarization makes the design of structures at atomic levels inevitable, as foreseen by Moore's law.
From these perspectives, it is necessary to concentrate further research efforts into controlling and manipulating quantum mechanical systems. This enables for example to encode quantum superposition states to tackle problems which are computationally NP hard and which therefore cannot be solved efficiently by classical computers. The only limitation affecting these solutions is the low scalability of existing quantum systems. Similarly, quantum communication schemes are devised to certify the secure transmission of quantum information, but are still limited by a low transmission bandwidth.
This thesis follows the guideline defined by these research projects and aims to further increase the scalability of the quantum mechanical systems required to perform these tasks. The method used here is to encode quantum states into photons generated by spontaneous parametric down-conversion (SPDC). An intrinsic limitation of photons is that the scalability of quantum information schemes employing them is limited by the low detection efficiency of commercial single photon detectors. This is addressed by encoding higher dimensional quantum states into two photons, increasing the scalability of the scheme in comparison to multi-photon states. Further on, the encoding of quantum information into the emission-time degree of freedom improves its applicability to long distance quantum communication schemes. By doing that, the intrinsic limitations of other schemes based on the encoding into the momentum and polarization degree of freedom are overcome.
This work presents results on a scalable experimental implementation of time-energy encoded higher dimensional states, demonstrating the feasibility of the scheme. Further tools are defined and used to characterize the properties of the prepared quantum states, such as their entanglement, their dimension and their preparation fidelity. Finally, the method of quantum state tomography is used to fully determine the underlying quantum states at the cost of an increased measurement effort and thus operation time. It is at this point that results obtained from the research field of compressed sensing help to decrease the necessary number of measurements. This scheme is compared with an adaptive tomography scheme designed to offer an additional reconstruction speedup. These results display the scalability of the scheme to bipartite dimensions higher than 2x8, equivalent to the encoding of quantum information into more than 6 qubits.Es ist in den letzten Jahren immer deutlicher geworden, dass weitere Forschung zur Untersuchung von quantenmechanischen Systemen durchgeführt werden muss um die wachsenden Probleme in der heutigen Informationstechnologie zu adressieren. Insbesondere sticht hier die exponentiell wachsende Nachfrage nach Computerressourcen und nach sicheren Kommunikationsprotokollen mit hoher Bandbreite hervor, um der weiter wachsenden Datengenerationsrate standzuhalten. Dies stösst auf fundamentale Grenzen, wie die erforderliche Miniaturisierung von Prozessorstrukturen (CPUs) auf atomare Dimensionen demonstriert. Von dieser Perspektive her ist es erforderlich weitere Forschung zur Kontrolle und Manipulation von Quantenzuständen durchzuführen, wie sie zum Beispiel im Feld der Quanteninformation erfolgt ist. Diese Strategie ermöglicht es von weiteren Eigenschaften der Quantenmechanik, wie zum Beispiel der Präparation von Superpositionszuständen, Gebrauch zu machen. Dies ist insbesondere relevant, da es ermöglicht NP harte Probleme zu lösen, die durch klassische Computer nicht effizient gelöst werden können. Allerdings sind bisher experimentell realisierte quantenmechanische Systeme noch nicht skalierbar genug um den Anforderungen der klassischen Technologie gerecht zu werden. Ähnlichen Argumenten folgend sind Quantenkommunikationssysteme, die die Sicherheit von Kommunikationsprotokolle zertifizieren können, noch nicht in der Lage angemessene Bandbreiten zu gewährleisten. Diese Doktorarbeit gliedert sich diesen Forschungsprojekten an, mit dem Ziel die Skalierbarkeit von quantenmechanischen Systemen zu vergrössern und entsprechend den genannten Anforderungen gerecht zu machen. Die Strategie die hier verfolgt wird basiert auf die Kodierung von Quantenzuständen in Photonenpaare, die durch den Prozess der Spontanen Parametrischen Down-conversion (SPDC) erzeugt werden. Dieses Verfahren bringt allerdings eine limitierte Skalierbarkeit der Quantensysteme mit sich, da die Detektionseffizienz von kommerziell erhältlichen Einzelphotonendetektoren limitiert ist. Dieses Problem wird in dieser Arbeit umgangen indem die Quantenzustände in höher dimensionale Hilberträume eines Zweiphotonenzustands kodiert werden, was einen deutlichen Vorteil gegenüber der Kodierung in einen Mehrphotonenzustand darstellt. Darüber hinaus ermöglicht die Kodierung der Quantenzustände in den Emissionszeit Freiheitsgrad der Photonen intrinsische Vorteile bei ihrer Anwendung auf die Quantenkommunikation. Hier ist insbesondere der Vorteil gegenüber der Kodierung in den Impuls- und Polarisationsfreiheitsgrad gemeint, die durch deutliche Einschränkungen bei der Transmission über lange Strecken gekennzeichnet sind. Mit einem Augenmerk auf diese Ziele wird in dieser Arbeit die experimentelle Umsetzbarkeit des beschriebenen Schemas gezeigt. Dies wurde durch die Anwendung von geeigneten Maßen wie die Verschränkung, Dimension und Präparationsfidelity auf die generierten Zustände quantifiziert. Insbesondere bei der Abschätzung der Fidelity wurde von Forschungsergebnissen rund um Compressed Sensing Gebrauch gemacht und weiter mit einem adaptiven Messschema kombiniert, um die effektive Betriebszeit dieser Systeme zu verringern. Dies ist für die weitere skalierbare Anwendung zur Quanteninformationsverarbeitung von Vorteil. Die Ergebnisse verdeutlichen, dass eine Skalierbarkeit der Dimension des Systems auf grösser als 2x8 Dimensionen, äquivalent zur Dimension eines 6-Qubit Zustands, in der Reichweite einer experimentellen Umsetzung liegt.
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Yuen, Henry Ph D. Massachusetts Institute of Technology. "Games, protocols, and quantum entanglement." Thesis, Massachusetts Institute of Technology, 2016. http://hdl.handle.net/1721.1/107364.
Full textAbstract:
Thesis: Ph. D., Massachusetts Institute of Technology, Department of Electrical Engineering and Computer Science, 2016.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 177-184).
Quantum entanglement has evolved from being "spooky action at a distance" to being a fundamental information-theoretic resource, extending the frontiers of what is possible in communications, computation, and cryptography. It gives rise to non-local correlations that can be harnessed to perform tasks such as certified randomness generation and classical verification of quantum computation. However, these same non-local correlations also pose a challenge when analyzing complexity-theoretic or cryptographic protocols in a quantum world: the soundness or security of the protocol may no longer hold in the presence of entangled adversaries. This thesis presents several results involving games and protocols with entangled parties; in each result, we introduce new techniques and methods to analyze soundness against adversaries that can manipulate quantum entanglement. First, we present a protocol wherein a classical verifer interacts with eight non-communicating quantum devices, and for all integer N the verifier can statistically certify that the devices have produced N bits of randomness that is E-close to uniform, while only using O(log³ 1/[epsilon]) bits of seed randomness. We call this an infinite randomness expansion protocol, because the amount N of certified output randomness is independent of the verifier's seed length. Entanglement is both a blessing and a curse for this protocol: on one hand, the devices need entanglement in order to successfully generate randomness to pass the protocol. But on the other hand, the devices may try to use entanglement to cheat and pass the protocol without producing additional randomness. We show that the monogamous nature of entanglement prevents this from happening. Next, this thesis studies the parallel repetition of games with entangled players. Raz's classical parallel repetition theorem (SICOMP 1998) is an influential result in complexity theory showing that the maximum success probability of unentangled players in a two-player game must decrease exponentially when the game is repeated in parallel. Its proof is highly non-trivial, and a major open question is whether it extends to the case of entangled players. We make progress on this question in several ways. First, we present an efficient transformation on games called "anchoring" that converts any k-player game G into a k-player game G[upside down upper case T] such that the entangled value of its n-fold parallel repetition, Gn[upside down upper case T], is exponentially small in n (provided that the entangled value of G is less than 1). Furthermore, the transformation is completeness preserving, in that if the entangled value of G is 1, then the entangled value of Gn[upside down upper case T] is also 1. This yields the first gap amplification procedure for general entangled games that achieves exponential decay. We also show that parallel repetition of a game causes the entangled value to decrease at a polynomial rate with the number of repetitions. In particular, this gives the first proof that the entangled value of a parallel repeated game converges to 0 for all games who entangled value is less than 1. The third result of this thesis on entangled parallel repetition is an improved analysis of the parallel repetition of free games with entangled players. Free games are those where the players' questions are independent of each other. We show how to use the fact that the DISJOINTNESS problem of size N can be solved with O([square root]N) qubits of quantum communication in order to speed up the rate of decay for the parallel repetition: given a free game G with entangled value 1 - [epsilon], its n-fold parallel repetition Gn has entangled value at most (1 - [epsilon]³/²)[omega](n/s), where s is the length of the players' answers in G. In contrast, the best parallel repetition theorem for free games with unentangled players, due to Barak, et al. (RANDOM 2009), shows that for a free game G with entangled value 1 - [delta], the classical value of Gn is at most (1 - [epsilon]² )[omega](n/s), which is a slower rate of decay. This suggests a separation between the behavior of entangled games and unentangled games under parallel repetition. In the final part of this thesis, we examine message authentication in a quantum world. Message authentication is a fundamental task in cryptography that ensures data integrity when communicating over an insecure channel. We consider two settings. One is classical authentication against quantum attacks. The other is total quantum authentication of quantum data. We give a new class of security definitions for both modes of message authentication. Our definitions capture and strengthen several existing definitions, including that of Boneh-Zhandry (EUROCRYPT 2013), which pertains to superposition attacks on classical authentication schemes, as well as the definition of Barnum, et al. (FOCS 2002), which addresses total authentication of quantum data. Our definitions give strong characterizations for what a quantum adversary is able to do in a message authentication protocol, even when the adversary has quantum side information that is entangled with the message state. We argue that, in the "one time" setting, our definitions are the strongest possible. We prove that our security definition for total quantum authentication has some surprising implications, such as the ability to reuse the key whenever verification is successful, and a conceptually simple quantum key distribution protocol. We then give several constructions of protocols that satisfy our security definitions: (1) we show that the classical Wegman-Carter scheme with 3-universal hashing is secure against quantum adversaries with quantum-side information; (2) we present a protocol based on unitary designs that achieves total quantum authentication, and (3) we show that using the classical Wegman- Carter scheme to authenticate in complementary bases yields a form of total quantum authentication, with bounded key leakage.
by Henry Yuen.
Ph. D.
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Timothy, H. Hsieh Timothy (Timothy Hwa-wei). "Topological materials and quantum entanglement." Thesis, Massachusetts Institute of Technology, 2015. http://hdl.handle.net/1721.1/103228.
Full textAbstract:
Thesis: Ph. D., Massachusetts Institute of Technology, Department of Physics, 2015.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 83-91).
As the title implies, this thesis consists of two main topics: materials which realize topological phases of matter and applications of the concept of entanglement in understanding topological phases and their transitions. The first part will focus on a particular class of materials called topological crystalline insulators (TCI), which are bulk insulators with metallic boundary states protected by crystal mirror symmetries. The realization of TCIs in the SnTe class of materials and the anti-perovskite family will be described. The second part will focus on using entanglement notions to probe a topological phase transition, based on a single topological wavefunction. This is achieved by performing extensive partitions of the wavefunction, such as a checkerboard partition. Implementing this technique in one dimension naturally involves the use of tensor networks, which will be reviewed and then utilized.
by Timothy H. Hsieh.
Ph. D.
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Suh, Sunok Josephine. "Entanglement in gauge/ gravity duality." Thesis, Massachusetts Institute of Technology, 2015. http://hdl.handle.net/1721.1/103223.
Full textAbstract:
Thesis: Ph. D., Massachusetts Institute of Technology, Department of Physics, 2015.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 73-77).
In this thesis, we present studies that elucidate the relationship between entanglement in strongly coupled gauge theories and the geometry of their gravity duals. In the first, we find that in a certain class of time-dependent states which have a gravity dual in which a black hole forms, the entanglement entropy of large regions grows linearly in time, following the growth of certain time-like slices in the interior of the black hole. In the second, we find a unified prescription in the gravity dual for calculating the action of the entanglement Hamiltonian associated to an arbitrary spatial region in a given holographic state. In particular, we find that the linearized perturbation of the metric caused by the entanglement Hamiltonian propagates from the bulk entangling surface.
by Sunok Josephine Suh.
Ph. D.
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Parker, Rachel Frances. "Quantum entanglement and fault-tolerance." Thesis, University of Cambridge, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.615063.
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Lin, Ho-Chih. "Local approach to quantum entanglement." Thesis, University College London (University of London), 2008. http://discovery.ucl.ac.uk/1446283/.
Full textAbstract:
Quantum entanglement is the key property that makes quantum information theory different from its classical counterpart and is also a valuable physical resource with massive potential for technological applications. However, our understanding of entanglement is still far from com plete despite intense research activities. Like other physical resources, the first step towards exploiting them fully is to know how to quantify. There are many reasons to focus on the en tanglement of continuous-variable states since the underlying degrees of freedom of physical systems carrying quantum information are frequently continuous, rather than discrete. Much of the effort has been concentrated on Gaussian states, because these are common as the ground or thermal states of optical modes. Within this framework, many interesting topics have been stud ied and some significant progress made. Nevertheless, non-Gaussian states are also extremely important this is especially so in condensed-phase systems, where harmonic behaviour in any degree of freedom is likely to be only an approximation. So far, there is little knowledge about the quantification of entanglement in non-Gaussian states. This thesis aims to contribute to the active field of research in quantum entanglement by introducing a new approach to the analysis of entanglement, especially in continuous-variable states, and shows that it leads to the first systematic quantification of the (local) entanglement in arbitrary bipartite non-Gaussian states. By applying this local approach, many new insights can be gained. Notably, local entanglements of systems with smooth wavefunctions are fully characterised by the derived simple expressions, provided the wavefunction is known. The local (logarithmic) negativity of any two-mode mixed states can be directly computed from the closed-form formulae given. For multi-mode mixed states, this approach provides a scheme that permits much simpler numerical computation for quantifying entanglement than is generally possible from directly computing the full entanglement of the system.
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Woodhead, William Robert. "Applications of holography and entanglement." Thesis, University of Southampton, 2017. https://eprints.soton.ac.uk/415894/.
Full textAbstract:
In this thesis we will investigate a number of topics on the applications of the gauge-gravity duality to topics in condensed matter physics and quantum entanglement. This duality is a conjectured equivalence between type IIB string theory on asymptotically anti-de Sitter backgrounds with certain quantum field theories in one dimension less. Using this conjecture we can model strongly-coupled quantum systems using classical gravity duals which provide novel methods for calculating otherwise computationally inaccessible quantum properties. We will use this for the following applications: • We study a novel method for introducing broken translational symmetry into a holographic model whilst retaining homogeneity in the field equations. We demonstrate that this leads to a finite DC conductivity and shows features of heavy fermion models in the AC conductivity. • We explore the nature of real time scalar correlators in holographic models of critical systems that possess a non-relativistic scaling symmetry. Specifically we explore systems with dual Schrödinger or Lifshitz scaling symmetries, and discuss the problems that arise when trying to apply the standard framework of real time holography to these systems. • We provide an explicit counterexample to the holographic F-theorem, and an analytic argument that shows that this violation is not specific to the model in consideration but is rather a more general property of a class of holographic systems. • Finally we introduce a holographic renormalization scheme for the entanglement entropy based on the standard framework of holographic renormalization. We connect this to the field theory via the replica trick and use it to calculate a number of explicit examples both analytically and numerically.
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Bauml, Stefan. "Applications and detection of entanglement." Thesis, University of Bristol, 2015. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.685543.
Full textAbstract:
Entanglement is an effect at the heart of quantum mechanics, which is both useful as a resource for information theoretic tasks and important in the fundamental understanding of physics. While bipartite maximal entangled states are well understood, applications as well as detection of other forms of entanglement - multipartite, mixed, bound - still provide many open questions. The fact that some bound entangled states can be used as a resource for quantum key distribution motivates the question of how such states can be distributed between distant parties. One way would be a conventional quantum repeater starting with distillable entanglement between the nodes and performing subsequent steps of distillation and entanglement swapping. It is, however, an intriguing question whether key can be obtained between distant parties if only bound entanglement is available between the nodes of the repeater. In this work, we provide upper bounds on the key obtainable from a quantum repeater that can be severely limited for bound entangled input states. Understanding the role of entanglement in macroscopic systems is an important task. A particular interesting question is whether there are connections between the entanglement in a given system and its thermodynamic variables. It has previously been shown that for some Hamiltonians all states below a certain internal energy are entangled. We extend this result to higher internal energies by also considering the entropy of the system. This allows us to theoretically certify entanglement of thermal states at higher temperatures than previous results. Another application of entanglement is as an additional resource for classical communication via a quantum channel. While the classical capacity of a channel assisted by maximal entanglement is known, it is an open question whether for any entangled state, there always exists a channel the classical capacity of which can be enhanced by using the state as an additional resource. We show that this is the case for one-way undistillable Werner states in small dimensions.
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Silva, Ralph Francisco. "Entanglement, nonlocality, postselection and thermodynamics." Thesis, University of Bristol, 2015. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.686187.
Full textAbstract:
In this second part of the thesis, we turn to the study of thermodynamics at the quantum scale, with a special focus on small thermal machines. To begin with, in Chapter 4, we look at the concept of a virtual temperature, as introduced in [43]. This is a temperature calculated for any pair of energy levels in a diagonal state by matching the ratio of its populations to the Gibbs state. The small quantum fridge introduced in Chapter 5, as well as all of the other small quantum thermal machines may be understood in terms of the virtual temperatures that they are able to generate within a system. We use the concept of virtual temperatures to construct an elegant and illuminating proof of the notion of complete passivity. A passive state [44] is one from which no work may be extracted from a unitary, while complete passivity refers to the property that no work can be extracted from multiple copies of a state.
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Spedalieri, Federico Maximiliano Preskill John P. "Characterizing entanglement in quantum information /." Diss., Pasadena, Calif. : California Institute of Technology, 2003. http://resolver.caltech.edu/CaltechETD:etd-05222003-121058.
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Lan, Shau-Yu. "Matter-light entanglement with cold." Diss., Atlanta, Ga. : Georgia Institute of Technology, 2008. http://hdl.handle.net/1853/28197.
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Thesis (M. S.)--Physics, Georgia Institute of Technology, 2009.Committee Chair: Kuzmich, Alex; Committee Member: Chapman, Michael; Committee Member: Citrin, David; Committee Member: Kennedy, T. A. Brian; Committee Member: Raman, Chandra
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CAPONIGRO, MICHELE. "Quantum Entanglement: Non-Local Implications." Doctoral thesis, Università degli studi di Bergamo, 2011. http://hdl.handle.net/10446/920.
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Sato, Yoshiki. "Holographic Entanglement Entropy in the dS/CFT Correspondence and Entanglement Entropy in the Sp(N) Model." 京都大学 (Kyoto University), 2016. http://hdl.handle.net/2433/215307.
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Riera, Graells Arnau. "Entanglement in Many Body Quantum Systems." Doctoral thesis, Universitat de Barcelona, 2010. http://hdl.handle.net/10803/1600.
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THESIS SUMMARYTEXT:
This thesis is made of two parts. In the first one, the issue of entanglement in many body systems is addressed. The concept of entanglement and some of the recent progress on the study of entropy of entanglement in many body quantum systems are reviewed. Emphasis is placed on the scaling properties of entropy for one-dimensional models at quantum phase transitions.
Then, we focus on the area-law scaling of the entanglement entropy. An explicit computation in arbitrary dimensions of the entanglement entropy of the ground state of a discretized scalar free field theory that shows the expected area law result is also presented. For this system, it is shown that area law scaling is a manifestation of a deeper reordering of the vacuum produced by majorization relations.
To finish this first part, the issue of how simple can a quantum system be such as to give a highly entangled ground state is addressed. In particular, we propose a Hamiltonian of a XX model with a ground state whose entropy scales linearly with the size of the block. It provides a simple example of a one dimensional system of spin-1/2 particles with nearest neighbour interactions that violates area-law for the entanglement entropy.
The second part of this thesis deals with the problem of simulating quantum mechanics for highly entangled systems. Two different approaches to this issue are considered. One consists of using ultra-cold atoms systems as quantum simulators. With this aim, some experimental techniques related to cold atoms that allow to simulate strongly correlated many body quantum systems are reviewed an explicit example of simulation is presented. In particular, we analyze how to achieve a Mott state of Laughlin wave functions in an optical lattice and study the consequences of considering anharmonic corrections to each single site potential expansion that were not taken into account until now.
Finally, a different approach to simulate strongly correlated systems is considered: to use small quantum computers to simulate them. An explicit quantum algorithm that creates the Laughlin state for an arbitrary number of particles n in the case of falling fraction equal to one is presented. We further prove the optimality of the circuit using permutation theory arguments and we compute exactly how entanglement develops along the action of each gate. We also discuss its experimental feasibility decomposing the qudits and the gates in terms of qubits and two qubit-gates as well as the generalization to arbitrary falling fraction.
KEYWORDS: Entanglement, Many body quantum systems, Quantum Information Condensed Matter, Cold atoms, Spin chains, Quantum simulator, Quantum computation.
"Entrellaçament quàntic en sistemes de molts cossos"
TEXT:
Aquesta tesi està composada per dues parts. En la primera, adrecem la qüestió de l'entrellaçament quàntic en els sistemes de molts cossos. Així, introduïm primer el concepte d'entrellaçament i revisem els progressos recents sobre aquest camp. A continuació, ens centrem la llei d'àrea per l'entropia d'entrellaçament i presentem un càlcul explícit d'aquesta entropia per a l'estat fonamental d'un camp escalar no interactuant obtenint la llei d'àrea esperada. Finalment, acabem aquesta part presentant un sistema molt senzill 1-dimensional que tot i tenir interaccions locals mostra una llei de volum per l'entropia.
En la segona part de la tesi tractem el problema de la simulació de sistemes quàntics altament entrellaçats. Considerem dos possibles vies per tractar aquest problema. Una d'elles consisteix en la utilització d'àtoms ultra-freds com a simuladors quàntics. En particular, analitzem un mètode per obtenir un estat producte de funcions d'ona de Laughlin en un xarxa òptica i estudiem les conseqüències de considerar la correcció anharmònica de l'expansió del potencial a cada pou de la xarxa. Finalment, considerem una altra aproximació a la simulació de sistemes fortament correlacionats: utilitzar petits ordinadors quàntics per a simular-los. Per il.lustrar aquest tipus de simulació, presentem un algoritme quàntic que crea un estat de Laughlin per un nombre arbitrari de partícules i en el cas de fracció d'ocupació 1.
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Aschwanden, Manuel. "A classical view of quantum entanglement /." Zürich : ETH, Eidgenössische Technische Hochschule Zürich, Department of Information, 2005. http://e-collection.ethbib.ethz.ch/show?type=dipl&nr=179.
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