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Author Bason, Mark G.; Viteau, Matthieu; Malossi, Nicola; Huillery, Paul; Arimondo, Ennio; Ciampini, Donatella; Fazio, Rosario; Giovannetti, Vittorio; Mannella, Riccardo; Morsch, Oliver
Title (down) High-fidelity quantum driving Type Journal Article
Year 2012 Publication Nature Physics Abbreviated Journal Nat. Phys.
Volume 8 Issue 2 Pages 147-152
Keywords fromIPMRAS
Abstract Accurately controlling a quantum system is a fundamental requirement in quantum information processing and the coherent manipulation of molecular systems. The ultimate goal in quantum control is to prepare a desired state with the highest fidelity allowed by the available resources and the experimental constraints. Here we experimentally implement two optimal high-fidelity control protocols using a two-level quantum system comprising Bose-Einstein condensates in optical lattices. The first is a short-cut protocol that reaches the maximum quantum-transformation speed compatible with the Heisenberg uncertainty principle. In the opposite limit, we realize the recently proposed transitionless superadiabatic protocols in which the system follows the instantaneous adiabatic ground state nearly perfectly. We demonstrate that superadiabatic protocols are extremely robust against control parameter variations, making them useful for practical applications.
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Call Number RPLAB @ gujma @ Serial 816
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Author Usmani, Imam; Clausen, Christoph; Bussières, Félix; Sangouard, Nicolas; Afzelius, Mikael; Gisin, Nicolas
Title (down) Heralded quantum entanglement between two crystals Type Journal Article
Year 2012 Publication Nature Photonics Abbreviated Journal Nat. Photon.
Volume 6 Issue 4 Pages 234-237
Keywords fromIPMRAS
Abstract Quantum networks must have the crucial ability to entangle quantum nodes. A prominent example is the quantum repeater, which allows the distance barrier of direct transmission of single photons to be overcome, provided remote quantum memories can be entangled in a heralded fashion. Here, we report the observation of heralded entanglement between two ensembles of rare-earth ions doped into separate crystals. A heralded single photon is sent through a 50/50 beamsplitter, creating a single-photon entangled state delocalized between two spatial modes. The quantum state of each mode is subsequently mapped onto a crystal, leading to an entangled state consisting of a single collective excitation delocalized between two crystals. This entanglement is revealed by mapping it back to optical modes and by estimating the concurrence of the retrieved light state. Our results highlight the potential of crystals doped with rare-earth ions for entangled quantum nodes and bring quantum networks based on solid-state resources one step closer.
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Call Number RPLAB @ gujma @ Serial 793
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Author Li, Mo; Pernice, W. H. P.; Xiong, C.; Baehr-Jones, T.; Hochberg, M.; Tang, H. X.
Title (down) Harnessing optical forces in integrated photonic circuits Type Journal Article
Year 2008 Publication Nature Abbreviated Journal Nature
Volume 456 Issue 7221 Pages 480-484
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ISSN 0028-0836 ISBN Medium
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Call Number RPLAB @ s @ Serial 425
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Author Lydersen, Lars; Wiechers, Carlos; Wittmann, Christoffer; Elser, Dominique; Skaar, Johannes; Makarov, Vadim
Title (down) Hacking commercial quantum cryptography systems by tailored bright illumination Type Journal Article
Year 2010 Publication Nature Photonics Abbreviated Journal Nat. Photon.
Volume 4 Issue 10 Pages 686 - 689
Keywords quantum cryptography, hacking, QKD, APD
Abstract The peculiar properties of quantum mechanics allow two remote parties to communicate a private, secret key, which is protected from eavesdropping by the laws of physics. So-called quantum key distribution (QKD) implementations always rely on detectors to measure the relevant quantum property of single photons. Here we demonstrate experimentally that the detectors in two commercially available QKD systems can be fully remote-controlled using specially tailored bright illumination. This makes it possible to tracelessly acquire the full secret key; we propose an eavesdropping apparatus built of off-the-shelf components. The loophole is likely to be present in most QKD systems using avalanche photodiodes to detect single photons. We believe that our findings are crucial for strengthening the security of practical QKD, by identifying and patching technological deficiencies.
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Call Number RPLAB @ gujma @ Serial 657
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Author Ghali, Mohsen; Ohtani1, Keita; Ohno, Yuzo; Ohno, Hideo
Title (down) Generation and control of polarization-entangled photons from GaAs island quantum dots by an electric field Type Journal Article
Year 2012 Publication Nature Communications Abbreviated Journal Nat. Comm.
Volume 3 Issue 661 Pages 6
Keywords fromIPMRAS
Abstract Semiconductor quantum dots are potential sources for generating polarization-entangled photons efficiently. The main prerequisite for such generation based on biexciton-exciton cascaded emission is to control the exciton fine-structure splitting. Among various techniques investigated for this purpose, an electric field is a promising means to facilitate the integration into optoelectronic devices. Here we demonstrate the generation of polarization-entangled photons from single GaAs quantum dots by an electric field. In contrast to previous studies, which were limited to In(Ga)As quantum dots, GaAs island quantum dots formed by a thickness fluctuation were used because they exhibit a larger oscillator strength and emit light with a shorter wavelength. A forward voltage was applied to a Schottky diode to control the fine-structure splitting. We observed a decrease and suppression in the fine-structure splitting of the studied single quantum dot with the field, which enabled us to generate polarization-entangled photons with a high fidelity of 0.72 ± 0.05.
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Call Number RPLAB @ gujma @ Serial 769
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Author Hase, Muneaki; Katsuragawa, Masayuki; Constantinescu, Anca Monia; Petek, Hrvoje
Title (down) Frequency comb generation at terahertz frequencies by coherent phonon excitation in silicon Type Journal Article
Year 2012 Publication Nature Photonics Abbreviated Journal Nat. Photon.
Volume 6 Issue Pages 243–247
Keywords fromIPMRAS
Abstract High-order nonlinear light–matter interactions in gases enable the generation of X-ray and attosecond light pulses, metrology and spectroscopy1. Optical nonlinearities in solid-state materials are particularly interesting for combining optical and electronic functions for high-bandwidth information processing2. Third-order nonlinear optical processes in silicon have been used to process optical signals with bandwidths greater than 1 GHz (ref. 2). However, fundamental physical processes for a silicon-based optical modulator in the terahertz bandwidth range have not yet been explored. Here, we demonstrate ultrafast phononic modulation of the optical index of silicon by irradiation with intense few-cycle femtosecond pulses. The anisotropic reflectivity modulation by the resonant Raman susceptibility at the fundamental frequency of the longitudinal optical phonon of silicon (15.6 THz) generates a frequency comb up to seventh order. All-optical >100 THz frequency comb generation is realized by harnessing the coherent atomic motion of the silicon crystalline lattice at its highest mechanical frequency.
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Call Number RPLAB @ gujma @ Serial 794
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Author Brida, G.; Genovese, M.; Ruo Berchera, I.
Title (down) Experimental realization of sub-shot-noise quantum imaging Type Journal Article
Year 2010 Publication Nature Photonics Abbreviated Journal Nat. Photon.
Volume 4 Issue 4 Pages 227-230
Keywords fromIPMRAS
Abstract The properties of quantum states have led to the development of new technologies, ranging from quantum information to quantum metrology. A recent field of research to emerge is quantum imaging, which aims to overcome the limits of classical imaging by making use of the spatial properties of quantum states of light . In particular, quantum correlations between twin beams represent a fundamental resource for these studies. One of the most interesting proposed schemes takes advantage of the spatial quantum correlations between parametric down-conversion light beams to realize sub-shot-noise imaging of weak absorbing objects, leading ideally to noise-free imaging. Here, we present the first experimental realization of this scheme, showing its potential to achieve a larger signal-to-noise ratio than classical imaging methods. This work represents the starting point for this quantum technology, which we anticipate will have applications when there is a requirement for low-photon-flux illumination (for example for use with biological samples).
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Call Number RPLAB @ gujma @ Serial 771
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Author Zhang, Qiang; Goebel, Alexander; Wagenknecht, Claudia; Chen, Yu-Ao; Zhao, Bo; Yang, Tao; Mair, Alois; Schmiedmayer, Jörg; Pan, Jian-Wei
Title (down) 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 Berlín, Guido; Brassard, Gilles; Bussières, Félix; Godbout, Nicolas; Slater, Joshua A.; Tittel, Wolfgang
Title (down) Experimental loss-tolerant quantum coin flipping Type Journal Article
Year 2011 Publication Nature Communications Abbreviated Journal Nat. Comm.
Volume 2 Issue 561 Pages 7
Keywords fromIPMRAS
Abstract Coin flipping is a cryptographic primitive in which two distrustful parties wish to generate a random bit to choose between two alternatives. This task is impossible to realize when it relies solely on the asynchronous exchange of classical bits: one dishonest player has complete control over the final outcome. It is only when coin flipping is supplemented with quantum communication that this problem can be alleviated, although partial bias remains. Unfortunately, practical systems are subject to loss of quantum data, which allows a cheater to force a bias that is complete or arbitrarily close to complete in all previous protocols and implementations. Here we report on the first experimental demonstration of a quantum coin-flipping protocol for which loss cannot be exploited to cheat better. By eliminating the problem of loss, which is unavoidable in any realistic setting, quantum coin flipping takes a significant step towards real-world applications of quantum communication.
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Call Number RPLAB @ gujma @ Serial 766
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Author Prevedel, Robert; Hamel, Deny R.; Colbeck, Roger; Fisher, Kent; Resch, Kevin J.
Title (down) 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 Dada, Adetunmise C.; Leach, Jonathan; Buller, Gerald S.; Padgett, Miles J.; Andersson, Erika
Title (down) Experimental high-dimensional two-photon entanglement and violations of generalized Bell inequalities Type Journal Article
Year 2011 Publication Nature Physics Abbreviated Journal Nat. Phys.
Volume 7 Issue 9 Pages 677-680
Keywords fromIPMRAS
Abstract Quantum entanglement plays a vital role in many quantum-information and communication tasks. Entangled states of higher-dimensional systems are of great interest owing to the extended possibilities they provide. For example, they enable the realization of new types of quantum information scheme that can offer higher-information-density coding and greater resilience to errors than can be achieved with entangled two-dimensional systems (see ref. and references therein). Closing the detection loophole in Bell test experiments is also more experimentally feasible when higher-dimensional entangled systems are used. We have measured previously untested correlations between two photons to experimentally demonstrate high-dimensional entangled states. We obtain violations of Bell-type inequalities generalized to d-dimensional systems up to d=12. Furthermore, the violations are strong enough to indicate genuine 11-dimensional entanglement. Our experiments use photons entangled in orbital angular momentum, generated through spontaneous parametric down-conversion, and manipulated using computer-controlled holograms.
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Call Number RPLAB @ gujma @ Serial 828
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Author Lu, Chao-Yang; Zhou, Xiao-Qi; Gühne, Otfried; Gao, Wei-Bo; Zhang, Jin; Yuan, Zhen-Sheng; Goebel, Alexander; Yang, Tao; Pan, Jian-Wei
Title (down) Experimental entanglement of six photons in graph states Type Journal Article
Year 2007 Publication Nature Physics Abbreviated Journal Nat. Phys.
Volume 3 Issue 2 Pages 91-95
Keywords fromIPMRAS
Abstract Graph states-multipartite entangled states that can be represented by mathematical graphs-are important resources for quantum computation, quantum error correction, studies of multiparticle entanglement and fundamental tests of non-locality and decoherence. Here, we demonstrate the experimental entanglement of six photons and engineering of multiqubit graph states. We have created two important examples of graph states, a six-photon Greenberger-Horne-Zeilinger state, the largest photonic Schrödinger cat so far, and a six-photon cluster state, a state-of-the-art `one-way quantum computer'. With small modifications, our method allows us, in principle, to create various further graph states, and therefore could open the way to experimental tests of, for example, quantum algorithms or loss- and fault-tolerant one-way quantum computation.
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Call Number RPLAB @ gujma @ Serial 796
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Author Toyabe, Shoichi; Sagawa, Takahiro; Ueda, Masahito; Muneyuki, Eiro; Sano, Masaki
Title (down) 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 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.
Title (down) 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 Korotkov, Alexander N.
Title (down) Entanglement preservation: The Sleeping Beauty approach Type Journal Article
Year 2012 Publication Nature Physics Abbreviated Journal Nat. Phys.
Volume 8 Issue 2 Pages 107-108
Keywords fromIPMRAS
Abstract Two-qubit entanglement can be preserved by partially measuring the qubits to leave them in a 'lethargic' state. The original state is restored using quantum measurement reversal after the qubits have travelled through a decoherence channel.
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Call Number RPLAB @ gujma @ Serial 814
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