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Author Dada, Adetunmise C.; Leach, Jonathan; Buller, Gerald S.; Padgett, Miles J.; Andersson, Erika
Title (up) 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 Prevedel, Robert; Hamel, Deny R.; Colbeck, Roger; Fisher, Kent; Resch, Kevin J.
Title (up) 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 Zhang, Qiang; Goebel, Alexander; Wagenknecht, Claudia; Chen, Yu-Ao; Zhao, Bo; Yang, Tao; Mair, Alois; Schmiedmayer, Jörg; Pan, Jian-Wei
Title (up) 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 Bason, Mark G.; Viteau, Matthieu; Malossi, Nicola; Huillery, Paul; Arimondo, Ennio; Ciampini, Donatella; Fazio, Rosario; Giovannetti, Vittorio; Mannella, Riccardo; Morsch, Oliver
Title (up) 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 Feofanov, A. K.; Oboznov, V. A.; Bol'Ginov, V. V.; Lisenfeld, J.; Poletto, S.; Ryazanov, V. V.; Rossolenko, A. N.; Khabipov, M.; Balashov, D.; Zorin, A. B.; Dmitriev, P. N.; Koshelets, V. P.; Ustinov, A. V.
Title (up) Implementation of superconductor/ferromagnet/ superconductor Type Journal Article
Year 2010 Publication Nature Physics Abbreviated Journal Nat. Phys.
Volume 6 Issue 8 Pages 593-597
Keywords fromIPMRAS
Abstract High operation speed and low energy consumption may allow the superconducting digital single-flux-quantum circuits to outperform traditional complementary metal-oxide-semiconductor logic. The remaining major obstacle towards high element densities on-chip is a relatively large cell size necessary to hold a magnetic flux quantum Φ0. Inserting a π-type Josephson junction in the cell is equivalent to applying flux Φ0/2 and thus makes it possible to solve this problem. Moreover, using π-junctions in superconducting qubits may help to protect them from noise. Here we demonstrate the operation of three superconducting circuits-two of them are classical and one quantum-that all utilize such π-phase shifters realized using superconductor/ferromagnet/superconductor sandwich technology. The classical circuits are based on single-flux-quantum cells, which are shown to be scalable and compatible with conventional niobium-based superconducting electronics. The quantum circuit is a π-biased phase qubit, for which we observe coherent Rabi oscillations. We find no degradation of the measured coherence time compared to that of a reference qubit without a π-junction.
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Call Number RPLAB @ gujma @ Serial 805
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Author Gustafsson, Martin V.; Santos, Paulo V.; Johansson, Göran; Delsing, Per
Title (up) Local probing of propagating acoustic waves in a gigahertz echo chamber Type Journal Article
Year 2012 Publication Nature Physics Abbreviated Journal Nat. Phys.
Volume 8 Issue 4 Pages 338-343
Keywords fromIPMRAS
Abstract In the same way that micro-mechanical resonators resemble guitar strings and drums, surface acoustic waves resemble the sound these instruments produce, but moving over a solid surface rather than through air. In contrast with oscillations in suspended resonators, such propagating mechanical waves have not before been studied near the quantum mechanical limits. Here, we demonstrate local probing of surface acoustic waves with a displacement sensitivity of 30amRMSHz-1/2 and detection sensitivity on the single-phonon level after averaging, at a frequency of 932MHz. Our probe is a piezoelectrically coupled single-electron transistor, which is sufficiently fast, non-destructive and localized to enable us to track pulses echoing back and forth in a long acoustic cavity, self-interfering and ringing the cavity up and down. We project that strong coupling to quantum circuits will enable new experiments, and hybrids using the unique features of surface acoustic waves. Prospects include quantum investigations of phonon-phonon interactions, and acoustic coupling to superconducting qubits for which we present favourable estimates.
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Call Number RPLAB @ gujma @ Serial 813
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Author Bylander, Jonas; Gustavsson, Simon; Yan, Fei; Yoshihara, Fumiki; Harrabi, Khalil; Fitch, George; Cory, David G.; Nakamura, Yasunobu; Tsai, Jaw-Shen; Oliver, William D.
Title (up) Noise spectroscopy through dynamical decoupling with a superconducting flux qubit Type Journal Article
Year 2011 Publication Nature Physics Abbreviated Journal Nat. Phys.
Volume 7 Issue 7 Pages 565-570
Keywords fromIPMRAS
Abstract Quantum coherence in natural and artificial spin systems is fundamental to applications ranging from quantum information science to magnetic-resonance imaging and identification. Several multipulse control sequences targeting generalized noise models have been developed to extend coherence by dynamically decoupling a spin system from its noisy environment. In any particular implementation, however, the efficacy of these methods is sensitive to the specific frequency distribution of the noise, suggesting that these same pulse sequences could also be used to probe the noise spectrum directly. Here we demonstrate noise spectroscopy by means of dynamical decoupling using a superconducting qubit with energy-relaxation time T1=12μs. We first demonstrate that dynamical decoupling improves the coherence time T2 in this system up to the T2=2T1 limit (pure dephasing times exceeding 100μs), and then leverage its filtering properties to probe the environmental noise over a frequency (f) range 0.2-20MHz, observing a 1/fα distribution with α<1. The characterization of environmental noise has broad utility for spin-resonance applications, enabling the design of optimized coherent-control methods, promoting device and materials engineering, and generally improving coherence.
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Call Number RPLAB @ gujma @ Serial 829
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Author Lupascu, Adrian
Title (up) Nonlinear dynamics: Quantum pendula locked in Type Journal Article
Year 2011 Publication Nature Physics Abbreviated Journal Nat. Phys.
Volume 7 Issue 2 Pages 100-101
Keywords fromIPMRAS
Abstract A study of the autoresonant behaviour of a superconducting pendulum reveals that quantum fluctuations determine only the initial oscillator motion and not its subsequent dynamics. This could be important in the development of more efficient methods for reading solid-state qubits.
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Call Number RPLAB @ gujma @ Serial 840
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Author Buchanan, Mark
Title (up) Nothing's impossible Type Manuscript
Year 2011 Publication Nature Physics Abbreviated Journal Nat. Phys.
Volume 7 Issue Pages 5
Keywords fromIPMRAS
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Call Number RPLAB @ gujma @ Serial 839
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Author Mariantoni, Matteo; Wang, H.; Bialczak, Radoslaw C.; Lenander, M.; Lucero, Erik; Neeley, M.; O'Connell, A. D.; Sank, D.; Weides, M.; Wenner, J.; Yamamoto, T.; Yin, Y.; Zhao, J.; Martinis, John M.; Cleland, A. N.
Title (up) Photon shell game in three-resonator circuit quantum electrodynamics Type Journal Article
Year 2011 Publication Nature Physics Abbreviated Journal Nat. Phys.
Volume 7 Issue 4 Pages 287-293
Keywords fromIPMRAS
Abstract The generation and control of quantum states of light constitute fundamental tasks in cavity quantum electrodynamics (QED). The superconducting realization of cavity QED, circuit QED (refs 11, 12, 13, 14), enables on-chip microwave photonics, where superconducting qubits control and measure individual photon states. A long-standing issue in cavity QED is the coherent transfer of photons between two or more resonators. Here, we use circuit QED to implement a three-resonator architecture on a single chip, where the resonators are interconnected by two superconducting phase qubits. We use this circuit to shuffle one- and two-photon Fock states between the three resonators, and demonstrate qubit-mediated vacuum Rabi swaps between two resonators. By shuffling superposition states we are also able to demonstrate the high-fidelity phase coherence of the transfer. Our results illustrate the potential for using multi-resonator circuits as photon quantum registers and for creating multipartite entanglement between delocalized bosonic modes.
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Call Number RPLAB @ gujma @ Serial 838
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Author Kim, Yong-Su; Lee, Jong-Chan; Kwon, Osung; Kim, Yoon-Ho
Title (up) Protecting entanglement from decoherence using weak measurement and quantum measurement reversal Type Journal Article
Year 2012 Publication Nature Physics Abbreviated Journal Nat. Phys.
Volume 8 Issue 2 Pages 117-120
Keywords fromIPMRAS
Abstract Decoherence, often caused by unavoidable coupling with the environment, leads to degradation of quantum coherence. For a multipartite quantum system, decoherence leads to degradation of entanglement and, in certain cases, entanglement sudden death. Tackling decoherence, thus, is a critical issue faced in quantum information, as entanglement is a vital resource for many quantum information applications including quantum computing, quantum cryptography, quantum teleportation and quantum metrology. Here, we propose and demonstrate a scheme to protect entanglement from decoherence. Our entanglement protection scheme makes use of the quantum measurement itself for actively battling against decoherence and it can effectively circumvent even entanglement sudden death.
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Call Number RPLAB @ gujma @ Serial 815
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Author Saffman, Mark
Title (up) 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 Raussendorf, Robert
Title (up) 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 Grinolds, M. S.; Maletinsky, P.; Hong, S.; Lukin, M. D.; Walsworth, R. L.; Yacoby, A.
Title (up) Quantum control of proximal spins using nanoscale magnetic resonance imaging Type Journal Article
Year 2011 Publication Nature Physics Abbreviated Journal Nat. Phys.
Volume 7 Issue 9 Pages 687-692
Keywords fromIPMRAS
Abstract Quantum control of individual spins in condensed-matter systems is an emerging field with wide-ranging applications in spintronics, quantum computation and sensitive magnetometry. Recent experiments have demonstrated the ability to address and manipulate single electron spins through either optical or electrical techniques. However, it is a challenge to extend individual-spin control to nanometre-scale multi-electron systems, as individual spins are often irresolvable with existing methods. Here we demonstrate that coherent individual-spin control can be achieved with few- nanometre resolution for proximal electron spins by carrying out single-spin magnetic resonance imaging (MRI), which is realized using a scanning-magnetic-field gradient that is both strong enough to achieve nanometre spatial resolution and sufficiently stable for coherent spin manipulations. We apply this scanning-field-gradient MRI technique to electronic spins in nitrogen-vacancy (NV) centres in diamond and achieve nanometre resolution in imaging, characterization and manipulation of individual spins. For NV centres, our results in individual-spin control demonstrate an improvement of nearly two orders of magnitude in spatial resolution when compared with conventional optical diffraction-limited techniques. This scanning-field-gradient microscope enables a wide range of applications including materials characterization, spin entanglement and nanoscale magnetometry.
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Call Number RPLAB @ gujma @ Serial 827
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Author Hollenberg, Lloyd C. L.
Title (up) Quantum control: Through the quantum chicane Type Journal Article
Year 2012 Publication Nature Physics Abbreviated Journal Nat. Phys.
Volume 8 Issue 2 Pages 113-114
Keywords fromIPMRAS
Abstract In quantum control there is an inherent tension between high fidelity requirements and the need for speed to avoid decoherence. A direct comparison of quantum control protocols at these two extremes indicates where the sweet spot may lie.
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Call Number RPLAB @ gujma @ Serial 812
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