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  • 1
    Publication Date: 2014-11-14
    Description: Topology, with its abstract mathematical constructs, often manifests itself in physics and has a pivotal role in our understanding of natural phenomena. Notably, the discovery of topological phases in condensed-matter systems has changed the modern conception of phases of matter. The global nature of topological ordering, however, makes direct experimental probing an outstanding challenge. Present experimental tools are mainly indirect and, as a result, are inadequate for studying the topology of physical systems at a fundamental level. Here we employ the exquisite control afforded by state-of-the-art superconducting quantum circuits to investigate topological properties of various quantum systems. The essence of our approach is to infer geometric curvature by measuring the deflection of quantum trajectories in the curved space of the Hamiltonian. Topological properties are then revealed by integrating the curvature over closed surfaces, a quantum analogue of the Gauss-Bonnet theorem. We benchmark our technique by investigating basic topological concepts of the historically important Haldane model after mapping the momentum space of this condensed-matter model to the parameter space of a single-qubit Hamiltonian. In addition to constructing the topological phase diagram, we are able to visualize the microscopic spin texture of the associated states and their evolution across a topological phase transition. Going beyond non-interacting systems, we demonstrate the power of our method by studying topology in an interacting quantum system. This required a new qubit architecture that allows for simultaneous control over every term in a two-qubit Hamiltonian. By exploring the parameter space of this Hamiltonian, we discover the emergence of an interaction-induced topological phase. Our work establishes a powerful, generalizable experimental platform to study topological phenomena in quantum systems.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Roushan, P -- Neill, C -- Chen, Yu -- Kolodrubetz, M -- Quintana, C -- Leung, N -- Fang, M -- Barends, R -- Campbell, B -- Chen, Z -- Chiaro, B -- Dunsworth, A -- Jeffrey, E -- Kelly, J -- Megrant, A -- Mutus, J -- O'Malley, P J J -- Sank, D -- Vainsencher, A -- Wenner, J -- White, T -- Polkovnikov, A -- Cleland, A N -- Martinis, J M -- England -- Nature. 2014 Nov 13;515(7526):241-4. doi: 10.1038/nature13891.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Department of Physics, University of California, Santa Barbara, California 93106-9530, USA. ; Department of Physics, Boston University, Boston, Massachusetts 02215, USA. ; 1] Department of Physics, University of California, Santa Barbara, California 93106-9530, USA [2] Google Inc., Santa Barbara, California 93117, USA.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/25391961" target="_blank"〉PubMed〈/a〉
    Print ISSN: 0028-0836
    Electronic ISSN: 1476-4687
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
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  • 2
    Publication Date: 2015-03-06
    Description: Quantum computing becomes viable when a quantum state can be protected from environment-induced error. If quantum bits (qubits) are sufficiently reliable, errors are sparse and quantum error correction (QEC) is capable of identifying and correcting them. Adding more qubits improves the preservation of states by guaranteeing that increasingly larger clusters of errors will not cause logical failure-a key requirement for large-scale systems. Using QEC to extend the qubit lifetime remains one of the outstanding experimental challenges in quantum computing. Here we report the protection of classical states from environmental bit-flip errors and demonstrate the suppression of these errors with increasing system size. We use a linear array of nine qubits, which is a natural step towards the two-dimensional surface code QEC scheme, and track errors as they occur by repeatedly performing projective quantum non-demolition parity measurements. Relative to a single physical qubit, we reduce the failure rate in retrieving an input state by a factor of 2.7 when using five of our nine qubits and by a factor of 8.5 when using all nine qubits after eight cycles. Additionally, we tomographically verify preservation of the non-classical Greenberger-Horne-Zeilinger state. The successful suppression of environment-induced errors will motivate further research into the many challenges associated with building a large-scale superconducting quantum computer.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Kelly, J -- Barends, R -- Fowler, A G -- Megrant, A -- Jeffrey, E -- White, T C -- Sank, D -- Mutus, J Y -- Campbell, B -- Chen, Yu -- Chen, Z -- Chiaro, B -- Dunsworth, A -- Hoi, I-C -- Neill, C -- O'Malley, P J J -- Quintana, C -- Roushan, P -- Vainsencher, A -- Wenner, J -- Cleland, A N -- Martinis, John M -- England -- Nature. 2015 Mar 5;519(7541):66-9. doi: 10.1038/nature14270.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Department of Physics, University of California, Santa Barbara, California 93106, USA. ; 1] Department of Physics, University of California, Santa Barbara, California 93106, USA [2] Centre for Quantum Computation and Communication Technology, School of Physics, The University of Melbourne, Victoria 3010, Australia. ; 1] Department of Physics, University of California, Santa Barbara, California 93106, USA [2] Department of Materials, University of California, Santa Barbara, California 93106, USA.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/25739628" target="_blank"〉PubMed〈/a〉
    Print ISSN: 0028-0836
    Electronic ISSN: 1476-4687
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
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  • 3
    ISSN: 1573-5079
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The early suggestion by Lozier and Butler (Photochem. Photobiol. 17, 133–137 (1973)) that EPR Signal II arises from radicals associated with the water-splitting process in PSII has been confirmed and extended over the intervening years. Recent work has identified the Signal II radicals, $$\begin{array}{*{20}c} {\mathop D\nolimits^{\begin{array}{*{20}c} + \\ . \\ \end{array} } } \\ \end{array}$$ and $$\begin{array}{*{20}c} {\mathop Z\nolimits^{\begin{array}{*{20}c} + \\ . \\ \end{array} } } \\ \end{array}$$ , with plastosemiquinone cation species. In the experiments presented here we have used ENDOR spectroscopy and D2O/H2O exchange to characterize these paramagnets in more detail. The ENDOR matrix region, which arises from protons which interact weakly with the unpaired electron spin, is well-resolved at 4 K and at least seven resonances are apparent. A number of hyperfine couplings in the 3–8 MHz range are observed and are suggested to arise from methyl or hydroxyl protons which occur as substituents on the plastosemiquinone cation ring or from amino acid protons hydrogen-bonded to the 1,4-hydroxyl groups. Orientation selection experiments are consistent with these possibilities. D2O/H2O exchange shows that the D+/Z+ site is accessible to solvent. However, the exchange occurs slowly and is not complete even after 72 hours which suggests that the free radicals are functionally isolated from solvent water.
    Type of Medium: Electronic Resource
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