Collinear source of polarization-entangled photon pairs at non-degenerate wavelengths

We report on a simple but highly efficient source of polarization-entangled photon pairs at non-degenerate wavelengths. The fully collinear configuration of the source enables very high coupling efficiency into a single optical mode and allows the use of long nonlinear crystals. With optimized dispersion compensation it is possible to use a free-running laser diode as pump source and to reach an entanglement fidelity of 99.4 % at rates as high as 27000 pairs/s per mW of pump power. This greatly enhances the practicality of the source for applications in quantum communication and metrology.Comment: 4 pages, 4 figures, accepted in Applied Physics Letter

Efficient generation of photonic entanglement and multiparty quantum communication

Entangled photons are at the heart of experimental quantum physics. They were used for the first fundamental tests of quantum theory, and became a basic building block for many novel quantum protocols, such as quantum cryptography, dense coding or teleportation. Therefore, the efficient generation of entangled photons, as well as their distribution and accurate analysis are of paramount importance, particularly with regard to the practicability of many applications of quantum communication. This thesis deals largely with the problem of efficient generation of photonic entanglement with the principal aim of developing a bright source of polarization-entangled photon pairs, which meets the requirements for reliable and economic operation of quantum communication prototypes and demonstrators. Our approach uses a correlated photon-pair emission in nonlinear process of spontaneous parametric down-conversion pumped by light coming from a compact and cheap blue laser diode. Two alternative source configurations are examined within the thesis. The first makes use of a well established concept of degenerate non-collinear emission from a single type-II nonlinear crystal and the second relies on a novel method where the emissions from two adjacent type-I phase-matched nonlinear crystals operated in collinear non-degenerate regime are coherently overlapped. The latter approach showed to be more effective, yielding a total detected rate of almost 10^6 pairs/s at >98 % quantum interference visibility of polarization correlations. This performance, together with the almost free of alignment operation of the system, suggest that it is an especially promising candidate for many future practical applications, including quantum cryptography, detector calibration or use in undergraduate lab courses. The second issue addressed within the thesis is the simplification and practical implementation of quantum-assisted solutions to multiparty communication tasks. While the recent rapid progress in the development of bright entangled photon-pair sources has been followed with ample experimental reports on two-party quantum communication tasks, the practical implementations of tasks for more than two parties have been held back, so far. This is mainly due to the requirement of multiparty entangled states, which are very difficult to be produced with current methods and moreover suffer from a high noise. We show that entanglement is not the only non-classical resource endowing the quantum multiparty information processing its power. Instead, only the sequential communication and transformation of a single qubit can be sufficient to accomplish certain tasks. This we prove for two distinct communication tasks, secret sharing and communication complexity. Whereas the goal of the first is to split a cryptographic key among several parties in a way that its reconstruction requires their collaboration, the latter aims at reducing the amount of communication during distributed computational tasks. Importantly, our qubit-assisted solutions to the problems are feasible with state-of-the-art technology. This we clearly demonstrate in the laboratory implementation for 6 and 5 parties, respectively, which is to the best of our knowledge the highest number of actively performing parties in a quantum protocol ever implemented. Thus, by successfully solving and implementing a cryptographic task as well as a task originating in computer science, we clearly illustrate the potential to introduce multiparty communication problems into real life.Verschränkte Photonen sind von zentralem Interesse im Bereich experimenteller Quantenphysik. Sie wurden für die ersten fundamentalen Tests der Quantentheorie verwendet und bilden die Grundlage bei der Realisierung vieler neuer Kommunikationsprotokolle die auf quantenmechanischen Effekten basieren, wie zum Beispiel Quantenkryptographie, "dense coding" oder Teleportation. Die effiziente Erzeugung verschränkter Photonen sowie deren genaue Analyse ist folglich von großer Bedeutung, insbesondere im Hinblick auf die Umsetzbarkeit der vielen Quantenkommunikationsanwendungen. Die vorliegende Arbeit behandelt im Wesentlichen das Problem der effizienten Erzeugung von Photon Verschränkung. Das Hauptaugenmerk liegt dabei auf der Entwicklung einer Quelle verschränkter Photonen, die den Anforderungen für einen zuverlässigen und wirtschaftlichen Betrieb in Beispielanwendungen der Quantenkommunikation genügt. Unser Ansatz verwendet die Emission korrelierter Photonen Paare im Prozess der spontanen parametrischen Fluoreszenz. Der Prozess wird mit Licht einer handlichen und billigen blauen Laserdiode gepumpt. Es werden zwei alternative Aufbauten für die Quelle betrachtet. Der erste verwendet das altbewährte Konzept der entarteten nicht-kollinearen Emission in einem einzelnen nichtlinearen Kristall vom Typ II. Der zweite Ansatz basiert auf einer neuen Methode in der die Emission zweier aneinaderliegender, phasenangepasster Kristalle vom Typ I kohärent überlagert wird. Die Phasenanpassung erfolgt dabei im kollinearen nicht-entarteten Zustand. Mit einer Rate von 10^6 Paaren in der Sekunde bei einem Interferenzkontrast der Polarisationskorrelationen von >98 % erwies sich die neue Methode als wesentlich effizienter. Diese Leistungsfähigkeit, in Verbindung mit einem nahezu justagefreien Betrieb, lässt dieses System vielversprechend für zukünftige praktische Anwendungen, wie Quantenkryptographie, Detektorkalibrierung oder Praktikumsversuche für Studenten erscheinen. Ein weiteres Thema das im Rahmen dieser Arbeit behandelt wird ist die Vereinfachung und Implementierung kommunikationstheoretischer Problemlösungen unter Zuhilfenahme quantenmechanischer Effekte. Während der rasante Fortschritt der letzten Jahre bei der Entwicklung von Quellen zur Erzeugung verschränkter Photonenpaare zu einer großen Anzahl von Veröffentlichungen auf dem Gebiet der Zwei-Parteien-Quantenkommunikation geführt hat, hielt sich die Zahl der Implementierungen von Protokollen mit mehr als zwei Parteien in Grenzen. Dies liegt hauptsächlich daran, dass die benötigten Mehr-Teilchen verschränkten Zustände mit dem heutigen Stand der Technik schwer zu produzieren sind und darüber hinaus hohes Rauschen aufweisen. Wir zeigen, dass Verschränkung nicht die einzige Ressource ist, die Mehrparteien-Quanten-Informationsverarbeitung ihre Stärke verleiht. Im Gegenteil, die sequentielle Kommunikation und Transformation eines einzelnen Qubits kann bereits ausreichend für die Lösung bestimmter Probleme sein. Dies zeigen wir anhand zweier verschiedener informationstheoretischer Problemstellungen, dem "secret sharing" und der Kommunikationskomplexität. Die erste befasst sich mit der Aufteilung eines kryptographischen Schlüssels auf mehrere Parteien in einer Weise, die für dessen Rekonstruktion die Zusammenarbeit aller Parteien erfordert. Die zweite zielt auf die Reduzierung der Kommunikation beim Lösen distributiver Berechnungen ab. Bemerkenswerterweise ist das hier verwendete qubit-basierte Lösungsverfahren mit dem heutigen Stand der Technik umsetzbar, was wir durch dessen Realisierung im Labor für 6 bzw. 5 Personen zeigen. Nach unserem Wissen ist dies die höchste Anzahl an aktiv agierenden Teilnehmern in einem Quantenkommunikationsprotokoll die je implementiert wurde. Die erfolgreiche Lösung und Implementierung von Problemstellungen aus den Bereichen der Kryptographie und der Informatik bringt somit Mehrparteien Quantenkommunikation einen Schritt näher an kommerzielle Anwendungen heran

Application of X-Ray Fluorescence Analysis in Investigations of Historical Monuments

Nuclear techniques and other techniques using ionising radiation represent a valuable tool in non-destructive diagnostics applied to archaeological finds and objects of arts, namely for determining the composition of materials used in the production of artefacts. X-ray fluorescence analysis, both in its energy form and in its wave dispersive form, is one of the most widespread methods using ionising radiation to study the elemental composition of materials. It is frequently used for studies of various cultural and historic relicts and objects of art. This work summarizes the authors’ experience with X-ray fluorescence analysis in investigating historical frescos namely by means of portable provide spectroscopic devices. The results of these measurements information on the composition of the pigments, enable the comparison of processes used in the fabrication of pigments by individual artists, and in many cases offer information on how to repair the damaged parts.

Remote water meter reading and it´s use in water industry

Bakalářská práce se zabývá technologií Smart Metering ve spojitosti s vodárenstvím. Teoretická část si klade za cíl seznámit čtenáře s problematikou měření proteklého objemu vody přes vodoměry a jeho dálkovým měřením. Cílem výzkumné části je navrhnout dvě nové možnosti využití těchto dálkových odečtů. Konkrétně pak jde o zvýšení tlaku na síti a sledování změny proteklého objemu do sítě a z toho vyplývající změnu ztrát vody na síti, či změnu množství odebrané vody v domácnostech v konkrétní bilanční zóně. Došli jsme k závěru, že díky dobrému technickému stavu na síti, kde byla měření prováděna, k žádným vyšším únikům vody nedošlo. Naopak spotřeba domácností se oproti měřením během stejného období za minulý rok zvedla v průměru o 2,1 %. Druhá část tohoto výzkumu se věnuje změnám chování spotřebitelů během celostátní karantény v souvislosti s pandemií nemoci COVID-19. Byl zaznamenán celkový přítok do vodovodní sítě, který se snížil v průměru o 3074 m³ denně především v důsledku omezení provozu některých průmyslových podniků, či uzavření restaurací, naopak nárůst v reprezentativní bilanční zóně obsahující obytné budovy byl průměrně až o 7% vyšší oproti normě.The bachelor thesis deals with Smart Metering technology in connection with water supply. The theoretical part aims to acquaint the reader with the issue of measuring the flowed volume of water through water meters and its remote measurement. The aim of the research is to suggest two new possibilities of using these remote water readings. Specifically, it is about increasing the pressure on the network and monitoring the change in the volume flowed into the network and the resulting change in water losses on the network, or a change in the amount of water taken in households in a particular balance zone. We came to the conclusion that due to the good technical condition on the network where the measurements were performed, there were no higher water leaks. On the contrary, water consumption in households increased by an average of 2.1 % compared to measurements during the same period last year. The second part of the research focuses on changes in consumer behavior during the national quarantine in connection with the COVID-19 pandemic. The total inflow into the water supply network was registered, which decreased by an average of 3074 m³ per day mainly due to working restrictions of some industrial companies or restaurant closures, while the increase in the representative balance zone containing residential buildings was up to 7 % higher than normal.546 - Katedra environmentálního inženýrstvívýborn

Precise energy of the 9.4 keV gamma transition observed in the 83Rb decay

The energy of the 9.4 keV γ-transition observed in the 83Rb decay was established to be 9405.8(3) eV. This energy value was obtained from photon spectrometry measurements of the differences in the energies of closely spaced lines. The result allows one to determine more precisely the energy of conversion electrons of the 9.4 keV transition, which represent a unique tool for energy calibration of the tritium beta spectrum and systematic measurements in the KATRIN neutrino mass determination experiment

Single Qubit Quantum Secret Sharing

We present a simple and practical protocol for the solution of a secure multiparty communication task, the secret sharing, and its experimental realization. In this protocol, a secret message is split among several parties in a way that its reconstruction require the collaboration of the participating parties. In the proposed scheme the parties solve the problem by a sequential communication of a single qubit. Moreover we show that our scheme is equivalent to the use of a multiparty entangled GHZ state but easier to realize and better scalable in practical applications.Comment: 5 pages, 2 figures, submitted December 29, 200

Experimental verification of energy correlations in entangled photon pairs

Properties of entangled photon pairs generated in spontaneous parametric down-conversion are investigated in interference experiments. Strong energy correlations are demonstrated in a direct way. If a signal photon is detected behind a narrow spectral filter, then interference appears in the Mach-Zehnder interferometer placed in the route of the idler photon, even if the path difference in the interferometer exceeds the coherence length of the light. Narrow time correlations of the detection instants are demonstrated for the same photon-pair source using the Hong-Ou-Mandel interferometer. Both these two effects may be exhibited only by an entangled state.Comment: 8 pages, 7 figure

Experimental quantum communication complexity

We prove that the fidelity of two exemplary communication complexity protocols, allowing for an N-1 bit communication, can be exponentially improved by N-1 (unentangled) qubit communication. Taking into account, for a fair comparison, all inefficiencies of state-of-the-art set-up, the experimental implementation outperforms the best classical protocol, making it the candidate for multi-party quantum communication applications.Comment: 4 pages, 2 eps figures, RevTEX4; submitted June 23, 200

A high-brightness source of polarization-entangled photons optimized for applications in free space

We present a simple but highly efficient source of polarization-entangled photons based on spontaneous parametric down-conversion (SPDC) in bulk periodically poled potassium titanyl phosphate crystals (PPKTP) pumped by a 405 nm laser diode. Utilizing one of the highest available nonlinear coefficients in a non-degenerate, collinear type-0 phase-matching configuration, we generate polarization entanglement via the crossed-crystal scheme and detect 0.64 million photon pair events/s/mW, while maintaining an overlap fidelity with the ideal Bell state of 0.98 at a pump power of 0.025 mW