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Author (down) Zurek, Wojciech Hubert openurl 
  Title Quantum Darwinism Type Journal Article
  Year 2009 Publication Nature Physics Abbreviated Journal Nat. Phys.  
  Volume 5 Issue 3 Pages 181-188  
  Keywords fromIPMRAS  
  Abstract Quantum Darwinism describes the proliferation, in the environment, of multiple records of selected states of a quantum system. It explains how the quantum fragility of a state of a single quantum system can lead to the classical robustness of states in their correlated multitude; shows how effective `wave-packet collapse' arises as a result of the proliferation throughout the environment of imprints of the state of the system; and provides a framework for the derivation of Born's rule, which relates the probabilities of detecting states to their amplitudes. Taken together, these three advances mark considerable progress towards settling the quantum measurement problem.  
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  Call Number RPLAB @ gujma @ Serial 799  
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Author (down) Zhu, J.; Christensen, J.; Jung, J.; Martin-Moreno, L.; Yin, X.; Fok, L.; Zhang, X.; Garcia-Vidal, F. J. openurl 
  Title A holey-structured metamaterial for acoustic deep-subwavelength imaging Type Journal Article
  Year 2011 Publication Nature Physics Abbreviated Journal Nat. Phys.  
  Volume 7 Issue 1 Pages 52-55  
  Keywords fromIPMRAS  
  Abstract For classical waves such as light or sound, diffraction sets a natural limit on how finely the details of an object can be recorded on its image. Recently, various optical superlenses based on the metamaterials concept have shown the possibility of overcoming the diffraction limit. Similar two-dimensional (2D) acoustic hyperlens designs have also been explored. Here we demonstrate a 3D holey-structured metamaterial that achieves acoustic imaging down to a feature size of λ/50. The evanescent field components of a subwavelength object are efficiently transmitted through the structure as a result of their strong coupling with Fabry-Pérot resonances inside the holey plate. This capability of acoustic imaging at a very deep-subwavelength scale may open the door for a broad range of applications, including medical ultrasonography, underwater sonar and ultrasonic non-destructive evaluation.  
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  Call Number RPLAB @ gujma @ Serial 809  
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Author (down) Zhang, Qiang; Goebel, Alexander; Wagenknecht, Claudia; Chen, Yu-Ao; Zhao, Bo; Yang, Tao; Mair, Alois; Schmiedmayer, Jörg; Pan, Jian-Wei openurl 
  Title Experimental quantum teleportation of a two-qubit composite system Type Journal Article
  Year 2006 Publication Nature Physics Abbreviated Journal Nat. Phys.  
  Volume 2 Issue 10 Pages 678-682  
  Keywords fromIPMRAS; quantum teleportation  
  Abstract Quantum teleportation, a way to transfer the state of a quantum system from one location to another, is central to quantum communication and plays an important role in a number of quantum computation protocols. Previous experimental demonstrations have been implemented with single photonic or ionic qubits. However, teleportation of single qubits is insufficient for a large-scale realization of quantum communication and computation. Here, we present the experimental realization of quantum teleportation of a two-qubit composite system. In the experiment, we develop and exploit a six-photon interferometer to teleport an arbitrary polarization state of two photons. The observed teleportation fidelities for different initial states are all well beyond the state estimation limit of 0.40 for a two-qubit system. Not only does our six-photon interferometer provide an important step towards teleportation of a complex system, it will also enable future experimental investigations on a number of fundamental quantum communication and computation protocols  
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  Call Number RPLAB @ gujma @ Serial 795  
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Author (down) Zakka-Bajjani, Eva; Nguyen, François; Lee, Minhyea; Vale, Leila R.; Simmonds, Raymond W.; Aumentado, José openurl 
  Title Quantum superposition of a single microwave photon in two different 'colour' states Type Journal Article
  Year 2011 Publication Nature Physics Abbreviated Journal Nat. Phys.  
  Volume 7 Issue 8 Pages 599-603  
  Keywords fromIPMRAS  
  Abstract Fully controlled coherent coupling of arbitrary harmonic oscillators is an important tool for processing quantum information. Coupling between quantum harmonic oscillators has previously been demonstrated in several physical systems using a two-level system as a mediating element. Direct interaction at the quantum level has only recently been realized by means of resonant coupling between trapped ions. Here we implement a tunable direct coupling between the microwave harmonics of a superconducting resonator by means of parametric frequency conversion. We accomplish this by coupling the mode currents of two harmonics through a superconducting quantum interference device (SQUID) and modulating its flux at the difference (~7GHz) of the harmonic frequencies. We deterministically prepare a single-photon Fock state and coherently manipulate it between multiple modes, effectively controlling it in a superposition of two different 'colours'. This parametric interaction can be described as a beamsplitter-like operation that couples different frequency modes. As such, it could be used to implement linear optical quantum computing protocols on-chip.  
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  Call Number RPLAB @ gujma @ Serial 822  
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Author (down) Vishveshwara, Smitha openurl 
  Title Topological qubits: A bit of both Type Journal Article
  Year 2011 Publication Nature Physics Abbreviated Journal Nat. Phys.  
  Volume 7 Issue Pages 450–451  
  Keywords fromIPMRAS  
  Abstract 'Standard' qubits have been implemented in diverse physical systems. Now, so-called topological qubits are coming into the limelight, and could potentially be used for decoherence-free quantum computing. Coupling these two types of qubit might enable devices that exploit the virtues of both.  
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  Call Number RPLAB @ gujma @ Serial 825  
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Author (down) Ursin, R.; Tiefenbacher, F.; Schmitt-Manderbach, T.; Weier, H.; Scheidl, T.; Lindenthal, M.; Blauensteiner, B.; Jennewein, T.; Perdigues, J.; Trojek, P.; Ömer, B.; Fürst, M.; Meyenburg, M.; Rarity, J.; Sodnik, Z.; Barbieri, C.; Weinfurter, H.; Zeilinger, A. openurl 
  Title Entanglement-based quantum communication over 144km Type Journal Article
  Year 2007 Publication Nature Physics Abbreviated Journal Nat. Phys.  
  Volume 3 Issue 7 Pages 481-486  
  Keywords fromIPMRAS  
  Abstract Quantum entanglement is the main resource to endow the field of quantum information processing with powers that exceed those of classical communication and computation. In view of applications such as quantum cryptography or quantum teleportation, extension of quantum-entanglement-based protocols to global distances is of considerable practical interest. Here we experimentally demonstrate entanglement-based quantum key distribution over 144km. One photon is measured locally at the Canary Island of La Palma, whereas the other is sent over an optical free-space link to Tenerife, where the Optical Ground Station of the European Space Agency acts as the receiver. This exceeds previous free-space experiments by more than an order of magnitude in distance, and is an essential step towards future satellite-based quantum communication and experimental tests on quantum physics in space.  
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  Call Number RPLAB @ gujma @ Serial 797  
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Author (down) Trabesinger, Andreas openurl 
  Title Quantum mechanics: Shaken foundations Type Journal Article
  Year 2009 Publication Nature Physics Abbreviated Journal Nat. Phys.  
  Volume 5 Issue 12 Pages 863  
  Keywords fromIPMRAS  
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  Call Number RPLAB @ gujma @ Serial 802  
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Author (down) Toyabe, Shoichi; Sagawa, Takahiro; Ueda, Masahito; Muneyuki, Eiro; Sano, Masaki openurl 
  Title Experimental demonstration of information-to-energy conversion and validation of the generalized Jarzynski equality Type Journal Article
  Year 2010 Publication Nature Physics Abbreviated Journal Nat. Phys.  
  Volume 6 Issue 12 Pages 988-992  
  Keywords fromIPMRAS  
  Abstract In 1929, Leo Szilard invented a feedback protocol in which a hypothetical intelligence called Maxwell's demon pumps heat from an isothermal environment and transduces it to work. After an intense controversy that lasted over eighty years; it was finally clarified that the demon's role does not contradict the second law of thermodynamics, implying that we can convert information to free energy in principle. Nevertheless, experimental demonstration of this information-to-energy conversion has been elusive. Here, we demonstrate that a nonequilibrium feedback manipulation of a Brownian particle based on information about its location achieves a Szilard-type information-energy conversion. Under real-time feedback control, the particle climbs up a spiral-stairs-like potential exerted by an electric field and obtains free energy larger than the amount of work performed on it. This enables us to verify the generalized Jarzynski equality, or a new fundamental principle of “information-heat engine” which converts information to energy by feedback control.  
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  Call Number RPLAB @ gujma @ Serial 831  
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Author (down) Shor, Peter W. openurl 
  Title Quantum information theory: The bits don't add up Type Journal Article
  Year 2009 Publication Nature Physics Abbreviated Journal Nat. Phys.  
  Volume 5 Issue Pages 247 - 248  
  Keywords fromIPMRAS  
  Abstract A counterexample to the 'additivity question', the most celebrated open problem in the mathematical theory of quantum information, casts doubt on the possibility of finding a simple expression for the information capacity of a quantum channel.  
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  Call Number RPLAB @ gujma @ Serial 800  
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Author (down) Saffman, Mark openurl 
  Title Quantum computing: A quantum telecom link Type Journal Article
  Year 2010 Publication Nature Physics Abbreviated Journal Nat. Phys.  
  Volume 6 Issue 11 Pages 838-839  
  Keywords fromIPMRAS  
  Abstract Converting data-carrying photons to telecommunication wavelengths enables distribution of quantum information over long distances.  
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  Call Number RPLAB @ gujma @ Serial 833  
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Author (down) Raussendorf, Robert openurl 
  Title Quantum computing: Shaking up ground states Type Journal Article
  Year 2010 Publication Nature Physics Abbreviated Journal Nat. Phys.  
  Volume 6 Issue 11 Pages 840-841  
  Keywords fromIPMRAS  
  Abstract Measurement-based quantum computation with an Affleck-Kennedy-Lieb-Tasaki state is experimentally realized for the first time.  
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  Call Number RPLAB @ gujma @ Serial 834  
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Author (down) Prevedel, Robert; Hamel, Deny R.; Colbeck, Roger; Fisher, Kent; Resch, Kevin J. openurl 
  Title Experimental investigation of the uncertainty principle in the presence of quantum memory and its application to witnessing entanglement Type Journal Article
  Year 2011 Publication Nature Physics Abbreviated Journal Nat. Phys.  
  Volume 7 Issue 10 Pages 757-761  
  Keywords fromIPMRAS  
  Abstract Heisenberg's uncertainty principle provides a fundamental limitation on the ability of an observer holding classical information to predict the outcome when one of two measurements is performed on a quantum system. However, an observer with access to a particle (stored in a quantum memory) which is entangled with the system generally has a reduced uncertainty: indeed, if the particle and system are maximally entangled, the observer can perfectly predict the outcome of whichever measurement is chosen. This effect has recently been quantified in a new entropic uncertainty relation. Here we experimentally investigate this relation, showing its effectiveness as an efficient entanglement witness. We use entangled photon pairs, an optical delay line serving as a simple quantum memory and fast, active feed-forward. Our results quantitatively agree with the new uncertainty relation. Our technique acts as a witness for almost all entangled states in our experiment as we obtain lower uncertainties than would be possible without the entangled particle.  
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  Call Number RPLAB @ gujma @ Serial 821  
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Author (down) Pirandola, Stefano; Mancini, Stefano; Lloyd, Seth; Braunstein, Samuel L. openurl 
  Title Continuous-variable quantum cryptography using two-way quantum communication Type Journal Article
  Year 2008 Publication Nature Physics Abbreviated Journal Nat. Phys.  
  Volume 4 Issue 9 Pages 726-730  
  Keywords fromIPMRAS  
  Abstract Quantum cryptography has recently been extended to continuous-variable systems, such as the bosonic modes of the electromagnetic field possessing continuous degrees of freedom. In particular, several cryptographic protocols have been proposed and experimentally implemented using bosonic modes with Gaussian statistics. These protocols have shown the possibility of reaching very high secret key rates, even in the presence of strong losses in the quantum communication channel. Despite this robustness to loss, their security can be affected by more general attacks where extra Gaussian noise is introduced by the eavesdropper. Here, we show a `hardware solution' for enhancing the security thresholds of these protocols. This is possible by extending them to two-way quantum communication where subsequent uses of the quantum channel are suitably combined. In the resulting two-way schemes, one of the honest parties assists the secret encoding of the other, with the chance of a non-trivial superadditive enhancement of the security thresholds. These results should enable the extension of quantum cryptography to more complex quantum communications.  
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  Call Number RPLAB @ gujma @ Serial 798  
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Author (down) Perseguers, S.; Lewenstein, M.; Acín, A.; Cirac, J. I. openurl 
  Title Quantum random networks Type Journal Article
  Year 2010 Publication Nature Physics Abbreviated Journal Nat. Phys.  
  Volume 6 Issue 7 Pages 539-543  
  Keywords fromIPMRAS  
  Abstract Quantum mechanics offers new possibilities to process and transmit information. In recent years, algorithms and cryptographic protocols exploiting the superposition principle and the existence of entangled states have been designed. They should allow us to realize communication and computational tasks that outperform any classical strategy. Here we show that quantum mechanics also provides fresh perspectives in the field of random networks. Already the simplest model of a classical random graph changes markedly when extended to the quantum case, where we obtain a distinct behaviour of the critical probabilities at which different subgraphs appear. In particular, in a network of N nodes, any quantum subgraph can be generated by local operations and classical communication if the entanglement between pairs of nodes scales as N-2. This result also opens up new vistas in the domain of quantum networks and their applications.  
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  Call Number RPLAB @ gujma @ Serial 804  
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Author (down) Nevou, L.; Liverini, V.; Friedli, P.; Castellano, F.; Bismuto, A.; Sigg, H.; Gramm, F.; Müller, E.; Faist, J. openurl 
  Title Current quantization in an optically driven electron pump based on self-assembled quantum dots Type Journal Article
  Year 2011 Publication Nature Physics Abbreviated Journal Nat. Phys.  
  Volume 7 Issue Pages 423–427  
  Keywords fromIPMRAS  
  Abstract The electronic structure of self-assembled semiconductor quantum dots consists of discrete atom-like states that can be populated with a well-defined number of electrons. This property can be used to fabricate a d.c. current standard that enables the unit of ampere to be independently defined. Here we report an optically pumped current source based on self-assembled InAs/GaAs quantum dots. The accuracy obtained so far is 10–1 and is limited by the uncertainty in the number of dots. At 10 K the device generates a current difference of 2.39 nA at a frequency of 1 kHz. The accuracy could be improved by site-selective growth techniques where the number of dots is fixed by pre-patterning. The results are promising for applications in electrical metrology, where a current standard is needed to close the so-called quantum metrological triangle.  
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  Call Number RPLAB @ gujma @ Serial 841  
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