135 research outputs found
Unconventional Magnetism in a Nitrogen-Based Analogue of Cupric Oxide
We have investigated the magnetic properties of CuNCN, the first
nitrogen-based analogue of cupric oxide, CuO. Our muon spin relaxation, nuclear
magnetic resonance and electron spin resonance studies reveal that classical
magnetic ordering is absent down to lowest temperatures. However, large
enhancement of spin correlations and unexpected inhomogeneous magnetism have
been observed below 80 K. We attribute this to a peculiar fragility of the
electronic state against weak perturbations due to geometrical frustration,
which selects between competing spin-liquid and more conventional frozen
states.Comment: 4 pages + 1 page of supplementary information, accepted for
publication in PR
Digital quantum simulation of spin models with circuit quantum electrodynamics
Systems of interacting quantum spins show a rich spectrum of quantum phases
and display interesting many-body dynamics. Computing characteristics of even
small systems on conventional computers poses significant challenges. A quantum
simulator has the potential to outperform standard computers in calculating the
evolution of complex quantum systems. Here, we perform a digital quantum
simulation of the paradigmatic Heisenberg and Ising interacting spin models
using a two transmon-qubit circuit quantum electrodynamics setup. We make use
of the exchange interaction naturally present in the simulator to construct a
digital decomposition of the model-specific evolution and extract its full
dynamics. This approach is universal and efficient, employing only resources
which are polynomial in the number of spins and indicates a path towards the
controlled simulation of general spin dynamics in superconducting qubit
platforms.Comment: 12 pages, 9 figure
Studying Light-Harvesting Models with Superconducting Circuits
The process of photosynthesis, the main source of energy in the animate
world, converts sunlight into chemical energy. The surprisingly high efficiency
of this process is believed to be enabled by an intricate interplay between the
quantum nature of molecular structures in photosynthetic complexes and their
interaction with the environment. Investigating these effects in biological
samples is challenging due to their complex and disordered structure. Here we
experimentally demonstrate a new approach for studying photosynthetic models
based on superconducting quantum circuits. In particular, we demonstrate the
unprecedented versatility and control of our method in an engineered three-site
model of a pigment protein complex with realistic parameters scaled down in
energy by a factor of . With this system we show that the excitation
transport between quantum coherent sites disordered in energy can be enabled
through the interaction with environmental noise. We also show that the
efficiency of the process is maximized for structured noise resembling
intramolecular phononic environments found in photosynthetic complexes.Comment: 8+12 pages, 4+12 figure
Contextuality without nonlocality in a superconducting quantum system.
Classical realism demands that system properties exist independently of whether they are measured, while noncontextuality demands that the results of measurements do not depend on what other measurements are performed in conjunction with them. The Bell-Kochen-Specker theorem states that noncontextual realism cannot reproduce the measurement statistics of a single three-level quantum system (qutrit). Noncontextual realistic models may thus be tested using a single qutrit without relying on the notion of quantum entanglement in contrast to Bell inequality tests. It is challenging to refute such models experimentally, since imperfections may introduce loopholes that enable a realist interpretation. Here we use a superconducting qutrit with deterministic, binary-outcome readouts to violate a noncontextuality inequality while addressing the detection, individual-existence and compatibility loopholes. This evidence of state-dependent contextuality also demonstrates the fitness of superconducting quantum circuits for fault-tolerant quantum computation in surface-code architectures, currently the most promising route to scalable quantum computing
Computation of Asteroid Proper Elements on the Grid
A procedure of gridification of the computation of asteroid proper orbital elements is described. The need to speed up the time consuming computations and make them more efficient is justified by the large increase of observational data expected from the next generation all sky surveys. We give the basic notion of proper elements and of the contemporary theories and methods used to compute them for different populations of objects. Proper elements for nearly 70,000 asteroids are derived since the beginning of use of the Grid infrastructure for the purpose. The average time for the catalogs update is significantly shortened with respect to the time needed with stand-alone workstations. We also present basics of the Grid computing, the concepts of Grid middleware and its Workload management system. The practical steps we undertook to efficiently gridify our application are described in full detail. We present the results of a comprehensive testing of the performance of different Grid sites, and offer some practical conclusions based on the benchmark results and on our experience. Finally, we propose some possibilities for the future work
A constructively critical review of change and innovation-related concepts: Towards conceptual and operational clarity
The aim of this paper is to examine and clarify the nomological network of change and innovation (CI)-related constructs. A literature review in this field revealed a number of interrelated constructs that have emerged over the last decades. We examine several such constructs—innovation, creativity, proactive behaviours, job crafting, voice, taking charge, personal initiative, submitting suggestions, and extra-role behaviours. Our conceptual analysis suggests each one of these constructs represents a specific component of CI-related behaviours. However, we also found that on occasion these concepts have been dysfunctionally operationalized with evidence of three dysfunctional effects: (a) construct confusion, (b) construct drift, and (c) construct contamination. Challenges for future research to enhance conceptual and operational clarity are discussed.This paper was supported by the British Academy: [Grant number SG110409] awarded to the first author and by UK Leverhulme Trust: [Grant number IN-2012-095] awarded to the second author
Argon milling induced decoherence mechanisms in superconducting quantum circuits
The fabrication of superconducting circuits requires multiple deposition,
etch and cleaning steps, each possibly introducing material property changes
and microscopic defects. In this work, we specifically investigate the process
of argon milling, a potentially coherence limiting step, using niobium and
aluminum superconducting resonators as a proxy for surface-limited behavior of
qubits. We find that niobium microwave resonators exhibit an order of magnitude
decrease in quality-factors after surface argon milling, while aluminum
resonators are resilient to the same process. Extensive analysis of the niobium
surface shows no change in the suboxide composition due to argon milling, while
two-tone spectroscopy measurements reveal an increase in two-level system
electrical dipole moments, indicating a structurally altered niobium oxide
hosting larger two-level system defects. However, a short dry etch can fully
recover the argon milling induced losses on niobium, offering a potential route
towards state-of-the-art overlap Josephson junction qubits with niobium
circuitry.Comment: Main text: 6 pages, 3 figures, 1 table. 5 appendices, with 6
additional figures and 3 additional tables. 62 reference
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