ALBERT

Description: Although the influence of the grain size on the mechanical properties of polycrystalline materials is well understood, the occurrence of depth-gradients of grain size, microstructure, and residual stresses in nanocrystalline thin films and their effect on the functional properties is a phenomenon which has not yet been studied in detail. Hence in this work, single-layered polycrystalline and mosaic epitaxial as well as multilayered CrN thin films were characterized by a combination of averaging as well as depth-resolved experimental techniques, such as cross-sectional X-ray nanodiffraction and small-angle cross-sectional nanoindentation. The results reveal the fundamental relationship between gradients of grain size, microstructure, and stresses, controlled by the film growth conditions, and gradients of hardness and elastic modulus. The effect of the compressive stress and structural defects associated with high particle energy on the mechanical properties of nanocrystalline thin films was found to be dominant over the grain size and crystallographic texture. These findings open the way to functionalize structure-property gradients in nanocrystalline thin films through microstructural design as demonstrated for multilayered CrN films.

Description: Author(s): S. Ramelow, A. Fedrizzi, A. Poppe, N. K. Langford, and A. Zeilinger Entangled photons play a pivotal role in the distribution of quantum information in quantum networks. However, the frequency bands for optimal transmission and storage of photons are often not the same. Here, we experimentally demonstrate the coherent frequency conversion of photons entangled in the... [Phys. Rev. A 85, 013845] Published Mon Jan 30, 2012

Description: In contrast to today's computers, quantum computers and information technologies may in future be able to store and transmit information not only in the state "0" or "1," but also in superpositions of the two; information will then be stored and transmitted in entangled quantum states. Zeilinger discusses recent advances toward using this principle for quantum cryptography and highlights studies into the entanglement (or controlled superposition) of several photons, atoms, or ions.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Zeilinger, A -- New York, N.Y. -- Science. 2000 Jul 21;289(5478):405-6.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/17840576" target="_blank"〉PubMed〈/a〉

Description: Quantum computers, besides offering substantial computational speedups, are also expected to preserve the privacy of a computation. We present an experimental demonstration of blind quantum computing in which the input, computation, and output all remain unknown to the computer. We exploit the conceptual framework of measurement-based quantum computation that enables a client to delegate a computation to a quantum server. Various blind delegated computations, including one- and two-qubit gates and the Deutsch and Grover quantum algorithms, are demonstrated. The client only needs to be able to prepare and transmit individual photonic qubits. Our demonstration is crucial for unconditionally secure quantum cloud computing and might become a key ingredient for real-life applications, especially when considering the challenges of making powerful quantum computers widely available.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Barz, Stefanie -- Kashefi, Elham -- Broadbent, Anne -- Fitzsimons, Joseph F -- Zeilinger, Anton -- Walther, Philip -- New York, N.Y. -- Science. 2012 Jan 20;335(6066):303-8. doi: 10.1126/science.1214707.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Vienna Center for Quantum Science and Technology, Faculty of Physics, University of Vienna, Boltzmanngasse 5, A-1090 Vienna, Austria. stefanie.barz@univie.ac.at〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/22267806" target="_blank"〉PubMed〈/a〉

Description: We demonstrate the distribution of quantum entanglement via optical free-space links to independent receivers separated by 600 m, with no line of sight between each other. A Bell inequality between those receivers is violated by more than four standard deviations, confirming the quality of the entanglement. This outdoor experiment represents a step toward satellite-based distributed quantum entanglement.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Aspelmeyer, Markus -- Bohm, Hannes R -- Gyatso, Tsewang -- Jennewein, Thomas -- Kaltenbaek, Rainer -- Lindenthal, Michael -- Molina-Terriza, Gabriel -- Poppe, Andreas -- Resch, Kevin -- Taraba, Michael -- Ursin, Rupert -- Walther, Philip -- Zeilinger, Anton -- New York, N.Y. -- Science. 2003 Aug 1;301(5633):621-3. Epub 2003 Jun 19.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Institut fur Experimentalphysik, Universitat Wien, Boltzmanngasse 5, A-1090 Wien, Austria. markus.aspelmeyer@quantum.at〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/12817085" target="_blank"〉PubMed〈/a〉

Description: In contrast to classical physics, quantum theory demands that not all properties can be simultaneously well defined; the Heisenberg uncertainty principle is a manifestation of this fact. Alternatives have been explored--notably theories relying on joint probability distributions or non-contextual hidden-variable models, in which the properties of a system are defined independently of their own measurement and any other measurements that are made. Various deep theoretical results imply that such theories are in conflict with quantum mechanics. Simpler cases demonstrating this conflict have been found and tested experimentally with pairs of quantum bits (qubits). Recently, an inequality satisfied by non-contextual hidden-variable models and violated by quantum mechanics for all states of two qubits was introduced and tested experimentally. A single three-state system (a qutrit) is the simplest system in which such a contradiction is possible; moreover, the contradiction cannot result from entanglement between subsystems, because such a three-state system is indivisible. Here we report an experiment with single photonic qutrits which provides evidence that no joint probability distribution describing the outcomes of all possible measurements--and, therefore, no non-contextual theory--can exist. Specifically, we observe a violation of the Bell-type inequality found by Klyachko, Can, Binicioglu and Shumovsky. Our results illustrate a deep incompatibility between quantum mechanics and classical physics that cannot in any way result from entanglement.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Lapkiewicz, Radek -- Li, Peizhe -- Schaeff, Christoph -- Langford, Nathan K -- Ramelow, Sven -- Wiesniak, Marcin -- Zeilinger, Anton -- England -- Nature. 2011 Jun 22;474(7352):490-3. doi: 10.1038/nature10119.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Vienna Center for Quantum Science and Technology, Faculty of Physics, University of Vienna, Boltzmanngasse 5, Vienna A-1090, Austria.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/21697945" target="_blank"〉PubMed〈/a〉

Description: Single photons are excellent quantum information carriers: they were used in the earliest demonstrations of entanglement and in the production of the highest-quality entanglement reported so far. However, current schemes for preparing, processing and measuring them are inefficient. For example, down-conversion provides heralded, but randomly timed, single photons, and linear optics gates are inherently probabilistic. Here we introduce a deterministic process--coherent photon conversion (CPC)--that provides a new way to generate and process complex, multiquanta states for photonic quantum information applications. The technique uses classically pumped nonlinearities to induce coherent oscillations between orthogonal states of multiple quantum excitations. One example of CPC, based on a pumped four-wave-mixing interaction, is shown to yield a single, versatile process that provides a full set of photonic quantum processing tools. This set satisfies the DiVincenzo criteria for a scalable quantum computing architecture, including deterministic multiqubit entanglement gates (based on a novel form of photon-photon interaction), high-quality heralded single- and multiphoton states free from higher-order imperfections, and robust, high-efficiency detection. It can also be used to produce heralded multiphoton entanglement, create optically switchable quantum circuits and implement an improved form of down-conversion with reduced higher-order effects. Such tools are valuable building blocks for many quantum-enabled technologies. Finally, using photonic crystal fibres we experimentally demonstrate quantum correlations arising from a four-colour nonlinear process suitable for CPC and use these measurements to study the feasibility of reaching the deterministic regime with current technology. Our scheme, which is based on interacting bosonic fields, is not restricted to optical systems but could also be implemented in optomechanical, electromechanical and superconducting systems with extremely strong intrinsic nonlinearities. Furthermore, exploiting higher-order nonlinearities with multiple pump fields yields a mechanism for multiparty mediation of the complex, coherent dynamics.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Langford, N K -- Ramelow, S -- Prevedel, R -- Munro, W J -- Milburn, G J -- Zeilinger, A -- England -- Nature. 2011 Oct 12;478(7369):360-3. doi: 10.1038/nature10463.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Vienna Center for Quantum Science and Technology, Faculty of Physics, University of Vienna, Boltzmanngasse 5, A-1090 Vienna, Austria. nathan.langford@univie.ac.at〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/21993627" target="_blank"〉PubMed〈/a〉

Description: The quantum internet is predicted to be the next-generation information processing platform, promising secure communication and an exponential speed-up in distributed computation. The distribution of single qubits over large distances via quantum teleportation is a key ingredient for realizing such a global platform. By using quantum teleportation, unknown quantum states can be transferred over arbitrary distances to a party whose location is unknown. Since the first experimental demonstrations of quantum teleportation of independent external qubits, an internal qubit and squeezed states, researchers have progressively extended the communication distance. Usually this occurs without active feed-forward of the classical Bell-state measurement result, which is an essential ingredient in future applications such as communication between quantum computers. The benchmark for a global quantum internet is quantum teleportation of independent qubits over a free-space link whose attenuation corresponds to the path between a satellite and a ground station. Here we report such an experiment, using active feed-forward in real time. The experiment uses two free-space optical links, quantum and classical, over 143 kilometres between the two Canary Islands of La Palma and Tenerife. To achieve this, we combine advanced techniques involving a frequency-uncorrelated polarization-entangled photon pair source, ultra-low-noise single-photon detectors and entanglement-assisted clock synchronization. The average teleported state fidelity is well beyond the classical limit of two-thirds. Furthermore, we confirm the quality of the quantum teleportation procedure without feed-forward by complete quantum process tomography. Our experiment verifies the maturity and applicability of such technologies in real-world scenarios, in particular for future satellite-based quantum teleportation.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Ma, Xiao-Song -- Herbst, Thomas -- Scheidl, Thomas -- Wang, Daqing -- Kropatschek, Sebastian -- Naylor, William -- Wittmann, Bernhard -- Mech, Alexandra -- Kofler, Johannes -- Anisimova, Elena -- Makarov, Vadim -- Jennewein, Thomas -- Ursin, Rupert -- Zeilinger, Anton -- England -- Nature. 2012 Sep 13;489(7415):269-73. doi: 10.1038/nature11472.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Institute for Quantum Optics and Quantum Information, Austrian Academy of Sciences, Boltzmanngasse 3, A-1090 Vienna, Austria.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/22951967" target="_blank"〉PubMed〈/a〉

Description: The violation of a Bell inequality is an experimental observation that forces the abandonment of a local realistic viewpoint--namely, one in which physical properties are (probabilistically) defined before and independently of measurement, and in which no physical influence can propagate faster than the speed of light. All such experimental violations require additional assumptions depending on their specific construction, making them vulnerable to so-called loopholes. Here we use entangled photons to violate a Bell inequality while closing the fair-sampling loophole, that is, without assuming that the sample of measured photons accurately represents the entire ensemble. To do this, we use the Eberhard form of Bell's inequality, which is not vulnerable to the fair-sampling assumption and which allows a lower collection efficiency than other forms. Technical improvements of the photon source and high-efficiency transition-edge sensors were crucial for achieving a sufficiently high collection efficiency. Our experiment makes the photon the first physical system for which each of the main loopholes has been closed, albeit in different experiments.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Giustina, Marissa -- Mech, Alexandra -- Ramelow, Sven -- Wittmann, Bernhard -- Kofler, Johannes -- Beyer, Jorn -- Lita, Adriana -- Calkins, Brice -- Gerrits, Thomas -- Nam, Sae Woo -- Ursin, Rupert -- Zeilinger, Anton -- England -- Nature. 2013 May 9;497(7448):227-30. doi: 10.1038/nature12012. Epub 2013 Apr 14.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Institute for Quantum Optics and Quantum Information, Austrian Academy of Sciences, Boltzmanngasse 3, Vienna 1090, Austria. marissa.giustina@univie.ac.at〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/23584590" target="_blank"〉PubMed〈/a〉