412 research outputs found
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 -qubit adiabatic quantum optimization system comprises hysteretic dc
SQUIDs and rf SQUID latches controlled by 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 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 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
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