514 research outputs found
Decoherence-protected quantum gates for a hybrid solid-state spin register
Protecting the dynamics of coupled quantum systems from decoherence by the
environment is a key challenge for solid-state quantum information processing.
An idle qubit can be efficiently insulated from the outside world via dynamical
decoupling, as has recently been demonstrated for individual solid-state
qubits. However, protection of qubit coherence during a multi-qubit gate poses
a non-trivial problem: in general the decoupling disrupts the inter-qubit
dynamics, and hence conflicts with gate operation. This problem is particularly
salient for hybrid systems, wherein different types of qubits evolve and
decohere at vastly different rates. Here we present the integration of
dynamical decoupling into quantum gates for a paradigmatic hybrid system, the
electron-nuclear spin register. Our design harnesses the internal resonance in
the coupled-spin system to resolve the conflict between gate operation and
decoupling. We experimentally demonstrate these gates on a two-qubit register
in diamond operating at room temperature. Quantum tomography reveals that the
qubits involved in the gate operation are protected as accurately as idle
qubits. We further illustrate the power of our design by executing Grover's
quantum search algorithm, achieving fidelities above 90% even though the
execution time exceeds the electron spin dephasing time by two orders of
magnitude. Our results directly enable decoherence-protected interface gates
between different types of promising solid-state qubits. Ultimately, quantum
gates with integrated decoupling may enable reaching the accuracy threshold for
fault-tolerant quantum information processing with solid-state devices.Comment: This is original submitted version of the paper. The revised and
finalized version is in print, and is subjected to the embargo and other
editorial restrictions of the Nature journa
Harnessing nuclear spin polarization fluctuations in a semiconductor nanowire
Soon after the first measurements of nuclear magnetic resonance (NMR) in a
condensed matter system, Bloch predicted the presence of statistical
fluctuations proportional to in the polarization of an ensemble of
spins. First observed by Sleator et al., so-called "spin noise" has
recently emerged as a critical ingredient in nanometer-scale magnetic resonance
imaging (nanoMRI). This prominence is a direct result of MRI resolution
improving to better than 100 nm^3, a size-scale in which statistical spin
fluctuations begin to dominate the polarization dynamics. We demonstrate a
technique that creates spin order in nanometer-scale ensembles of nuclear spins
by harnessing these fluctuations to produce polarizations both larger and
narrower than the natural thermal distribution. We focus on ensembles
containing ~10^6 phosphorus and hydrogen spins associated with single InP and
GaP nanowires (NWs) and their hydrogen-containing adsorbate layers. We monitor,
control, and capture fluctuations in the ensemble's spin polarization in
real-time and store them for extended periods. This selective capture of large
polarization fluctuations may provide a route for enhancing the weak magnetic
signals produced by nanometer-scale volumes of nuclear spins. The scheme may
also prove useful for initializing the nuclear hyperfine field of electron spin
qubits in the solid-state.Comment: 18 pages, 5 figure
From quantum fusiliers to high-performance networks
Our objective was to design a quantum repeater capable of achieving one
million entangled pairs per second over a distance of 1000km. We failed, but
not by much. In this letter we will describe the series of developments that
permitted us to approach our goal. We will describe a mechanism that permits
the creation of entanglement between two qubits, connected by fibre, with
probability arbitrarily close to one and in constant time. This mechanism may
be extended to ensure that the entanglement has high fidelity without
compromising these properties. Finally, we describe how this may be used to
construct a quantum repeater that is capable of creating a linear quantum
network connecting two distant qubits with high fidelity. The creation rate is
shown to be a function of the maximum distance between two adjacent quantum
repeaters.Comment: 2 figures, Comments welcom
Linking Hydrothermal Geochemistry to Organismal Physiology: Physiological Versatility in Riftia pachyptila from Sedimented and Basalt-hosted Vents
Much of what is known regarding Riftia pachyptila physiology is based on the wealth of studies of tubeworms living at diffuse flows along the fast-spreading, basalt-hosted East Pacific Rise (EPR). These studies have collectively suggested that Riftia pachyptila and its chemoautotrophic symbionts are physiologically specialized, highly productive associations relying on hydrogen sulfide and oxygen to generate energy for carbon fixation, and the symbiont's nitrate reduction to ammonia for energy and biosynthesis. However, Riftia also flourish in sediment-hosted vents, which are markedly different in geochemistry than basalt-hosted systems. Here we present data from shipboard physiological studies and global quantitative proteomic analyses of Riftia pachyptila trophosome tissue recovered from tubeworms residing in the EPR and the Guaymas basin, a sedimented, hydrothermal vent field. We observed marked differences in symbiont nitrogen metabolism in both the respirometric and proteomic data. The proteomic data further suggest that Riftia associations in Guaymas may utilize different sulfur compounds for energy generation, may have an increased capacity for energy storage, and may play a role in degrading exogenous organic carbon. Together these data reveal that Riftia symbionts are far more physiologically plastic than previously considered, and that -contrary to previous assertions- Riftia do assimilate reduced nitrogen in some habitats. These observations raise new hypotheses regarding adaptations to the geochemical diversity of habitats occupied by Riftia, and the degree to which the environment influences symbiont physiology and evolution
Metabolic suppression in thecosomatous pteropods as an effect of low temperature and hypoxia in the eastern tropical North Pacific
Author Posting. © The Author(s), 2011. This is the author's version of the work. It is posted here by permission of Springer for personal use, not for redistribution. The definitive version was published in Marine Biology 159 (2012): 1955-1967, doi:10.1007/s00227-012-1982-x.Many pteropod species in the eastern tropical north Pacific Ocean migrate vertically each day, transporting organic matter and respiratory carbon below the thermocline. These migrations take species into cold (15-10ºC) hypoxic water (< 20 µmol O2 kg-1) at depth. We measured the vertical distribution, oxygen consumption and ammonia excretion for seven species of pteropod, some of which migrate and some which remain in oxygenated surface waters throughout the day. Within the upper 200 meters of the water column, changes in water temperature result in a ~60-75% reduction in respiration for most species. All three species tested under hypoxic conditions responded to low O2 with an additional ~35-50% reduction in respiratory rate. Combined, low temperature and hypoxia suppress the metabolic rate of pteropods by ~80-90%. These results shed light on the ways in which expanding regions of hypoxia and surface ocean warming may impact pelagic ecology.This work was funded by National Science Foundation grants to K. Wishner and B. Seibel (OCE – 0526502 and OCE – 0851043) and to K. Daly (OCE – 0526545), the University of Rhode Island, and the Rhode Island Experimental Program to Stimulate Competitive Research Fellowship program.2013-06-3
Photonic quantum technologies
The first quantum technology, which harnesses uniquely quantum mechanical
effects for its core operation, has arrived in the form of commercially
available quantum key distribution systems that achieve enhanced security by
encoding information in photons such that information gained by an eavesdropper
can be detected. Anticipated future quantum technologies include large-scale
secure networks, enhanced measurement and lithography, and quantum information
processors, promising exponentially greater computation power for particular
tasks. Photonics is destined for a central role in such technologies owing to
the need for high-speed transmission and the outstanding low-noise properties
of photons. These technologies may use single photons or quantum states of
bright laser beams, or both, and will undoubtably apply and drive
state-of-the-art developments in photonics
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First measurement of neutrino oscillation parameters using neutrinos and antineutrinos by NOvA.
The NOvA experiment has seen a 4.4σ signal of ν[over ¯]_{e} appearance in a 2 GeV ν[over ¯]_{μ} beam at a distance of 810 km. Using 12.33×10^{20} protons on target delivered to the Fermilab NuMI neutrino beamline, the experiment recorded 27 ν[over ¯]_{μ}→ν[over ¯]_{e} candidates with a background of 10.3 and 102 ν[over ¯]_{μ}→ν[over ¯]_{μ} candidates. This new antineutrino data are combined with neutrino data to measure the parameters |Δm_{32}^{2}|=2.48_{-0.06}^{+0.11}×10^{-3} eV^{2}/c^{4} and sin^{2}θ_{23} in the ranges from (0.53-0.60) and (0.45-0.48) in the normal neutrino mass hierarchy. The data exclude most values near δ_{CP}=π/2 for the inverted mass hierarchy by more than 3σ and favor the normal neutrino mass hierarchy by 1.9σ and θ_{23} values in the upper octant by 1.6σ
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Observation of seasonal variation of atmospheric multiple-muon events in the NOvA Near Detector
Using two years of data from the NOvA Near Detector at Fermilab, we report a seasonal variation of cosmic ray induced multiple-muon (Nμ≥2) event rates which has an opposite phase to the seasonal variation in the atmospheric temperature. The strength of the seasonal multiple-muon variation is shown to increase as a function of the muon multiplicity. However, no significant dependence of the strength of the seasonal variation of the multiple-muon variation is seen as a function of the muon zenith angle, or the spatial or angular separation between the correlated muons
Search for sterile neutrino mixing in the MINOS long-baseline experiment
A search for depletion of the combined flux of active neutrino species over a 735 km baseline is reported using neutral-current interaction data recorded by the MINOS detectors in the NuMI neutrino beam. Such a depletion is not expected according to conventional interpretations of neutrino oscillation data involving the three known neutrino flavors. A depletion would be a signature of oscillations or decay to postulated noninteracting sterile neutrinos, scenarios not ruled out by existing data. From an exposure of 3.18×1020 protons on target in which neutrinos of energies between ~500¿¿MeV and 120 GeV are produced predominantly as ¿µ, the visible energy spectrum of candidate neutral-current reactions in the MINOS far detector is reconstructed. Comparison of this spectrum to that inferred from a similarly selected near-detector sample shows that of the portion of the ¿µ flux observed to disappear in charged-current interaction data, the fraction that could be converting to a sterile state is less than 52% at 90% confidence level (C.L.). The hypothesis that active neutrinos mix with a single sterile neutrino via oscillations is tested by fitting the data to various models. In the particular four-neutrino models considered, the mixing angles ¿24 and ¿34 are constrained to be less than 11° and 56° at 90% C.L., respectively. The possibility that active neutrinos may decay to sterile neutrinos is also investigated. Pure neutrino decay without oscillations is ruled out at 5.4 standard deviations. For the scenario in which active neutrinos decay into sterile states concurrently with neutrino oscillations, a lower limit is established for the neutrino decay lifetime t3/m3>2.1×10-12¿¿s/eV at 90% C.L
Postsynthesis modification of a cellulose acetate ultrafiltration membrane for applications in water and wastewater treatment
A technique for postsynthesis modification of a cellulose acetate ultrafiltration membrane with possible application in water and wastewater treatment is studied. The technique used an oxidizing agent (persulfate) to develop free radicals on the membrane surface, and that was expected to promote grafting of hydrophilic macromolecules (polyethylene glycol). A chain-transfer agent (2-mercaptoethanol) was tested to control the grafting process, avoiding the formation of long chains that usually lead to high permeability losses in other graft techniques. The modifications aimed at the decrease of the fouling susceptibility of the membrane studied. The possibility of an increase in rejection was also investigated. The membrane was characterized before and after modification, by attenuated total reflectance-Fourier transform-infrared spectroscopy, scanning electron microscopy, atomic force microscopy, and in terms of the rejection of neutral reference solutes. The information given by the different techniques of characterization provided strong evidences of the occurrence of modification, although permeation of (real) foulants was the decisive test. To obtain information about the fouling tendency of the nonmodified and modified membranes, two different kinds of foulants were used: a humic acid (usually found in surface waters) and textile auxiliaries (representing one of the most important industries in Portugal). The results showed an increase in the rejections of the humic acid, and significant improvements in the performance of the membrane with respect to fouling tendency in the case of the textile auxiliarie
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