The influence of dissolved copper on the production of domoic acid by Pseudo-nitzschia species in Monterey Bay, California : laboratory experiments and field observations

omoic acid (DA) is a neurotoxic amino acid produced by several members of the diatom genus Pseudo-nitzschia. Trophic transfer of DA has been implicated in the deaths of 100\u27s of marine birds and mammals along the central California coast. Although the physiological role of DA has not been well established, evidence herein strongly suggests that DA functions to buffer dissolved inorganic copper (Cu\u27). Evaluating the homeostatic function of DA with respect to copper metabolism gave rise to three major findings: 1) DA binds Cu\u27 with an avidity comparable to the L2 ligand class KcondCuDA=1.0x10¹² (pH 8.2, I=0.02), 2) P. multiseries is tolerant to wide fluctuations [Cu\u27] loadings (pCutotal 10.8-3.26) because of strain-specific modulation of free amino acids pools (FAA), with up to a 10-fold increase in DA accumulation (31fg DA/cell) in response to elevated [Cu\u27], 3) Cu\u27 and total DA concentrations were highly correlated during a field survey spanning 97 days along a 3 kilometer transect in Monterey Bay, CA (r\u3e=0.79, n=3, a=0.01). Cumulatively, these results establish DA\u27s significant influence on Cu homeostasis in Pseudo-nitzschia species

Extensive Conservation of Linkage Relationships Between Pea and Lentil Genetic Maps

A 560-cM linkage map consisting of 64 morphological, isozyme, and DNA markers, has been developed from an interspecific cross (Lens ervoides × L. Culinaris). In addition, nine markers were scored that assorted independently of any of the multilocus linkage groups. Comparison of this map with that established previously for Pisum sativum reveals eight regions in which linkages among marker loci appear to have been conserved since the divergence of the two genera. These conserved linkage groups constitute at least 250 cM, or approximately 40% of the known linkage map for Lens. The two genera represent disparate lineages within the legume tribe Vicease, indicating that all members of this tribe may possess linkage groups similar to those identified in Lens and Pisum. Instances where the Pisum and Lens maps differed included the regions surrounding the 45S ribosomal tandem repeats and the position and distribution of the genes encoding the small subunit of ribulose bisphosphate carboxylase. We also found a highly repeated sequence unique to Lens that maps within a linkage group shared between the two genera and a cDNA sequence that displays significant variation in copy number within the genus Len

Compound Josephson-junction coupler for flux qubits with minimal crosstalk

This is the published version, also available here: http://dx.doi.org/10.1103/PhysRevB.80.052506.An improved tunable coupling element for building networks of coupled rf-superconducting quantum interference device (rf-SQUID) flux qubits has been experimentally demonstrated. This new form of coupler, based on the compound Josephson-junction rf-SQUID, provides a sign and magnitude tunable mutual inductance between qubits with minimal nonlinear crosstalk from the coupler tuning parameter into the qubits. Quantitative agreement is shown between an effective one-dimensional model of the coupler’s potential and measurements of the coupler persistent current and susceptibility

Entanglement in a quantum annealing processor

Entanglement lies at the core of quantum algorithms designed to solve problems that are intractable by classical approaches. One such algorithm, quantum annealing (QA), provides a promising path to a practical quantum processor. We have built a series of scalable QA processors consisting of networks of manufactured interacting spins (qubits). Here, we use qubit tunneling spectroscopy to measure the energy eigenspectrum of two- and eight-qubit systems within one such processor, demonstrating quantum coherence in these systems. We present experimental evidence that, during a critical portion of QA, the qubits become entangled and that entanglement persists even as these systems reach equilibrium with a thermal environment. Our results provide an encouraging sign that QA is a viable technology for large-scale quantum computing.Comment: 13 pages, 8 figures, contact corresponding author for Supplementary Informatio

Probing High Frequency Noise with Macroscopic Resonant Tunneling

We have developed a method for extracting the high-frequency noise spectral density of an rf-SQUID flux qubit from macroscopic resonant tunneling (MRT) rate measurements. The extracted noise spectral density is consistent with that of an ohmic environment up to frequencies ~ 4 GHz. We have also derived an expression for the MRT lineshape expected for a noise spectral density consisting of such a broadband ohmic component and an additional strongly peaked low-frequency component. This hybrid model provides an excellent fit to experimental data across a range of tunneling amplitudes and temperatures

Geometrical dependence of low frequency noise in superconducting flux qubits

A general method for directly measuring the low-frequency flux noise (below 10 Hz) in compound Josephson junction superconducting flux qubits has been used to study a series of 85 devices of varying design. The variation in flux noise across sets of qubits with identical designs was observed to be small. However, the levels of flux noise systematically varied between qubit designs with strong dependence upon qubit wiring length and wiring width. Furthermore, qubits fabricated above a superconducting ground plane yielded lower noise than qubits without such a layer. These results support the hypothesis that localized magnetic impurities in the vicinity of the qubit wiring are a key source of low frequency flux noise in superconducting devices.Comment: 5 pages, 5 figure

A scalable readout system for a superconducting adiabatic quantum optimization system

We have designed, fabricated and tested an XY-addressable readout system that is specifically tailored for the reading of superconducting flux qubits in an integrated circuit that could enable adiabatic quantum optimization. In such a system, the flux qubits only need to be read at the end of an adiabatic evolution when quantum mechanical tunneling has been suppressed, thus simplifying many aspects of the readout process. The readout architecture for an $N$-qubit adiabatic quantum optimization system comprises $N$ hysteretic dc SQUIDs and $N$ rf SQUID latches controlled by $2\sqrt{N} + 2$ bias lines. The latching elements are coupled to the qubits and the dc SQUIDs are then coupled to the latching elements. This readout scheme provides two key advantages: First, the latching elements provide exceptional flux sensitivity that significantly exceeds what may be achieved by directly coupling the flux qubits to the dc SQUIDs using a practical mutual inductance. Second, the states of the latching elements are robust against the influence of ac currents generated by the switching of the hysteretic dc SQUIDs, thus allowing one to interrogate the latching elements repeatedly so as to mitigate the effects of stochastic switching of the dc SQUIDs. We demonstrate that it is possible to achieve single qubit read error rates of $<10^{-6}$ with this readout scheme. We have characterized the system-level performance of a 128-qubit readout system and have measured a readout error probability of $8\times10^{-5}$ in the presence of optimal latching element bias conditions.Comment: Updated for clarity, final versio

Probing Noise in Flux Qubits via Macroscopic Resonant Tunneling

Macroscopic resonant tunneling between the two lowest lying states of a bistable RF-SQUID is used to characterize noise in a flux qubit. Measurements of the incoherent decay rate as a function of flux bias revealed a Gaussian shaped profile that is not peaked at the resonance point, but is shifted to a bias at which the initial well is higher than the target well. The r.m.s. amplitude of the noise, which is proportional to the decoherence rate 1/T_2^*, was observed to be weakly dependent on temperature below 70 mK. Analysis of these results indicates that the dominant source of low frequency (1/f) flux noise in this device is a quantum mechanical environment in thermal equilibrium.Comment: 4 pages 4 figure