Noise correlations in a flux qubit with tunable tunnel coupling

We have measured flux-noise correlations in a tunable superconducting flux qubit. The device consists of two loops that independently control the qubit's energy splitting and tunnel coupling. Low frequency flux noise in the loops causes fluctuations of the qubit frequency and leads to dephasing. Since the noises in the two loops couple to different terms of the qubit Hamiltonian, a measurement of the dephasing rate at different bias points provides a way to extract both the amplitude and the sign of the noise correlations. We find that the flux fluctuations in the two loops are anti-correlated, consistent with a model where the flux noise is generated by randomly oriented unpaired spins on the metal surface.Comment: 7 pages, including supplementary materia

Synergistic Release of Ca2+ from IP3-Sensitive Stores Evoked by Synaptic Activation of mGluRs Paired with Backpropagating Action Potentials

AbstractIncreases in postsynaptic [Ca2+]i can result from Ca2+ entry through ligand-gated channels or voltage-gated Ca2+ channels, or through release from intracellular stores. Most attention has focused on entry through the N-methyl-D-aspartate (NMDA) receptor in causing [Ca2+]i increases since this pathway requires both presynaptic stimulation and postsynaptic depolarization, making it a central component in models of synaptic plasticity. Here, we report that repetitive synaptic activation of metabotropic glutamate receptors (mGluRs), paired with backpropagating action potentials, causes large, wave-like increases in [Ca2+]i predominantly in restricted regions of the proximal apical dendrites and soma of hippocampal CA1 pyramidal neurons. [Ca2+]i changes of several micromolars can be reached by regenerative release caused by the synergistic effect of mGluR-generated inositol 1,4,5-trisphosphate (IP3) and spike-evoked Ca2+ entry acting on the IP3 receptor

Single microwave-photon detector using an artificial Λ\Lambda-type three-level system

Single photon detection is a requisite technique in quantum-optics experiments in both the optical and the microwave domains. However, the energy of microwave quanta are four to five orders of magnitude less than their optical counterpart, making the efficient detection of single microwave photons extremely challenging. Here, we demonstrate the detection of a single microwave photon propagating through a waveguide. The detector is implemented with an "impedance-matched" artificial $\Lambda$ system comprising the dressed states of a driven superconducting qubit coupled to a microwave resonator. We attain a single-photon detection efficiency of $0.66 \pm 0.06$ with a reset time of $\sim 400$~ns. This detector can be exploited for various applications in quantum sensing, quantum communication and quantum information processing.Comment: 5 pages (4 figures) + 4 pages (5 figures

Dynamical decoupling and dephasing in interacting two-level systems

We implement dynamical decoupling techniques to mitigate noise and enhance the lifetime of an entangled state that is formed in a superconducting flux qubit coupled to a microscopic two-level system. By rapidly changing the qubit's transition frequency relative to the two-level system, we realize a refocusing pulse that reduces dephasing due to fluctuations in the transition frequencies, thereby improving the coherence time of the entangled state. The coupling coherence is further enhanced when applying multiple refocusing pulses, in agreement with our $1/f$ noise model. The results are applicable to any two-qubit system with transverse coupling, and they highlight the potential of decoupling techniques for improving two-qubit gate fidelities, an essential prerequisite for implementing fault-tolerant quantum computing

Functional and pharmacological characterization of a Shal-related K+ channel subunit in Zebrafish

<p>Abstract</p> <p>Background</p> <p>K⁺channels are diverse; both in terms of their function and their molecular composition. Shal subunits were first described in Drosophila. There are three mammalian orthologs, which are members of the Kv4 subfamily. They are involved in neuronal firing patterns as well as control of the cardiac action potential duration.</p> <p>Results</p> <p>Here, we report the biophysical and pharmacological characterization of zShal3, which is the ortholog of the mammalian Kv4.3 subunit, which in mammals is involved in action potential repolarization and gives rise to neuronal A-type K⁺currents involved in somatodendretic signal integration.</p> <p>Conclusion</p> <p>We demonstrate that zShal has similar functional and pharmacological characteristics compared to Kv4.3 and it is similarly regulated by pharmacological agents and by the Kv4 accessory subunit, NCS-1.</p

The GoodWork Project: An Overview

The Good Project is a large scale effort to identify individuals and institutions that exemplify good work -- work that is excellent in quality, socially responsible, and meaningful to its practitioners -- and to determine how best to increase the incidence of good work in our society. This paper is a comprehensive description of the GoodWork Project

Hydrogen generation by electrolysis of aqueous organic solutions

A device for electrolysis of an aqueous solution of an organic fuel. The electrolyte is a solid-state polymer membrane with anode and cathode catalysts on both surfaces for electro-oxidization and electro-reduction. A low-cost and portable hydrogen generator can be made based on the device with organic fuels such as methanol

Hydrogen generation by electrolysis of aqueous organic solutions

A device for electrolysis of an aqueous solution of an organic fuel. The electrolyte is a solid-state polymer membrane with anode and cathode catalysts on both surfaces for electro-oxidization and electro-reduction. A low-cost and portable hydrogen generator can be made based on the device with organic fuels such as methanol

Lithium in garnet as a tracer of subduction zone metamorphic reactions: The record in ultrahigh-pressure metapelites at Lago di Cignana, Italy

Lithium is of great interest as a tracer of metamorphic reactions and related fluid-mineral interactions because of its potential to isotopically fractionate during inter- and intracrystalline diffusional processes. Study of its transfer through subduction zones, based on study of arc volcanic and metamorphic rocks, can yield insight regarding ocean-to-mantle chemical cycling. We investigated major- and trace-element concentrations and delta Li-7 in garnet in ultrahigh-pressure (UHP) Lago di Cignana metasedimentary rocks, relating these observations to reconstructed prograde devolatilization history. In all garnet crystals we studied, heavy rare earth elements (HREEs), Y, and Li showed strong zoning, with elevated concentrations in cores (15-50 ppm Li) and marked high-concentration anomalies (up to 117 ppm Li, 5500 ppm Y; little or no major-element shift) as growth annuli, in which some crystals showed subtle elevation in delta Li-7 greater than analytical error of similar to 3 parts per thousand (2 sigma). Rutile inclusions appeared abruptly at annuli and outward toward rims, accompanied by inclusions of a highly zoned, Ca- and rare earth element-rich phase and decreased Nb concentrations in garnet. These relationships are interpreted to reflect prograde garnet-forming reaction(s), in part involving titanite breakdown to stabilize rutile, which resulted in delivery of more abundant Y and HREEs at surfaces of growing garnet crystals to produce annuli. Co-enrichments in Li and Y + REEs are attributed to mutual incorporation via charge-coupled substitutions; thus, increased Li uptake was a passive consequence of elevated concentrations of Y + REEs. The small-scale fluctuations in delta Li-7 (overall range of similar to 9 parts per thousand) observed in some crystals may correlate with abrupt shifts in major-and trace-element concentrations, suggesting that changes in reactant phases exerted some control on the evolution of delta Li-7. For one garnet crystal, late-stage growth following partial resorption produced deviation in major- and trace-element compositions, including Li concentration, accompanied by a 10 parts per thousand-15 parts per thousand negative shift in delta Li-7, perhaps reflecting a change in the mechanism of incorporation or source of Li. These results highlight the value of measuring the major- and trace-element and isotope compositions of garnets in high-pressure and UHP metamorphic rocks in which matrix mineral assemblages are extensively overprinted by recrystallization during exhumation histories. Lithium concentrations and isotope compositions of the garnets can add valuable information regarding prograde (and retrograde) reaction history, kinetics of porphyroblast growth, intracrystalline diffusion, and fluid-rock interactions. This work, integrated with previous study of devolatilization in the Schistes Lustres/Cignana metasedimentary suite, indicates retention of a large fraction of the initially subducted sedimentary Li budget to depths approaching those beneath volcanic fronts, despite the redistribution of this Li among mineral phases during complex mineral reaction histories