1,879 research outputs found
Quantum sensing with arbitrary frequency resolution
Quantum sensing takes advantage of well controlled quantum systems for
performing measurements with high sensitivity and precision. We have
implemented a concept for quantum sensing with arbitrary frequency resolution,
independent of the qubit probe and limited only by the stability of an external
synchronization clock. Our concept makes use of quantum lock-in detection to
continuously probe a signal of interest. Using the electronic spin of a single
nitrogen vacancy center in diamond, we demonstrate detection of oscillating
magnetic fields with a frequency resolution of 70 uHz over a MHz bandwidth. The
continuous sampling further guarantees an excellent sensitivity, reaching a
signal-to-noise ratio in excess of 10,000:1 for a 170 nT test signal measured
during a one-hour interval. Our technique has applications in magnetic
resonance spectroscopy, quantum simulation, and sensitive signal detection.Comment: Manuscript resubmitted to Science. Includes Supplementary Material
High resolution quantum sensing with shaped control pulses
We investigate the application of amplitude-shaped control pulses for
enhancing the time and frequency resolution of multipulse quantum sensing
sequences. Using the electronic spin of a single nitrogen vacancy center in
diamond and up to 10,000 coherent microwave pulses with a cosine square
envelope, we demonstrate 0.6 ps timing resolution for the interpulse delay.
This represents a refinement by over 3 orders of magnitude compared to the 2 ns
hardware sampling. We apply the method for the detection of external AC
magnetic fields and nuclear magnetic resonance signals of carbon-13 spins with
high spectral resolution. Our method is simple to implement and especially
useful for quantum applications that require fast phase gates, many control
pulses, and high fidelity.Comment: 5 pages, 4 figures, plus supplemental materia
Observing biogeochemical cycles at global scales with profiling floats and gliders: prospects for a global array
Chemical and biological sensor technologies have advanced rapidly in the past five years. Sensors that require low power and operate for multiple years are now available for oxygen, nitrate, and a variety of bio-optical properties that serve as proxies for important components of the carbon cycle (e.g., particulate organic carbon). These sensors have all been deployed successfully for long periods, in some cases more than three years, on platforms such as profiling floats or gliders. Technologies for pH, pCO2, and particulate inorganic carbon are maturing rapidly as well. These sensors could serve as the enabling technology for a global biogeochemical observing system that might operate on a scale comparable to the current Argo array. Here, we review the scientific motivation and the prospects for a global observing system for ocean biogeochemistry
Substellar companions and isolated planetary mass objects from protostellar disc fragmentation
Self-gravitating protostellar discs are unstable to fragmentation if the gas
can cool on a time scale that is short compared to the orbital period. We use a
combination of hydrodynamic simulations and N-body orbit integrations to study
the long term evolution of a fragmenting disc with an initial mass ratio to the
star of M_disc/M_star = 0.1. For a disc which is initially unstable across a
range of radii, a combination of collapse and subsequent accretion yields
substellar objects with a spectrum of masses extending (for a Solar mass star)
up to ~0.01 M_sun. Subsequent gravitational evolution ejects most of the lower
mass objects within a few million years, leaving a small number of very massive
planets or brown dwarfs in eccentric orbits at moderately small radii. Based on
these results, systems such as HD 168443 -- in which the companions are close
to or beyond the deuterium burning limit -- appear to be the best candidates to
have formed via gravitational instability. If massive substellar companions
originate from disc fragmentation, while lower-mass planetary companions
originate from core accretion, the metallicity distribution of stars which host
massive substellar companions at radii of ~1 au should differ from that of
stars with lower mass planetary companions.Comment: 5 pages, accepted for publication in MNRA
Tracking the precession of single nuclear spins by weak measurements
Nuclear magnetic resonance (NMR) spectroscopy is a powerful technique for
analyzing the structure and function of molecules, and for performing
three-dimensional imaging of the spin density. At the heart of NMR
spectrometers is the detection of electromagnetic radiation, in the form of a
free induction decay (FID) signal, generated by nuclei precessing around an
applied magnetic field. While conventional NMR requires signals from 1e12 or
more nuclei, recent advances in sensitive magnetometry have dramatically
lowered this number to a level where few or even individual nuclear spins can
be detected. It is natural to ask whether continuous FID detection can still be
applied at the single spin level, or whether quantum back-action modifies or
even suppresses the NMR response. Here we report on tracking of single nuclear
spin precession using periodic weak measurements. Our experimental system
consists of carbon-13 nuclear spins in diamond that are weakly interacting with
the electronic spin of a nearby nitrogen-vacancy center, acting as an optically
readable meter qubit. We observe and minimize two important effects of quantum
back-action: measurement-induced decoherence and frequency synchronization with
the sampling clock. We use periodic weak measurements to demonstrate sensitive,
high-resolution NMR spectroscopy of multiple nuclear spins with a priori
unknown frequencies. Our method may provide the optimum route for performing
single-molecule NMR at atomic resolution.Comment: 29 pages including methods and extended data figures; for
supplementary material, see v1 of this submissio
Three-dimensional localization spectroscopy of individual nuclear spins with sub-Angstrom resolution
We report on precise localization spectroscopy experiments of individual 13C
nuclear spins near a central electronic sensor spin in a diamond chip. By
detecting the nuclear free precession signals in rapidly switchable external
magnetic fields, we retrieve the three-dimensional spatial coordinates of the
nuclear spins with sub-Angstrom resolution and for distances beyond 10
Angstroms. We further show that the Fermi contact contribution can be
constrained by measuring the nuclear g-factor enhancement. The presented method
will be useful for mapping the atomic-scale structure of single molecules, an
ambitious yet important goal of nanoscale nuclear magnetic resonance
spectroscopy
Annealing of Silicate Dust by Nebular Shocks at 10 AU
Silicate dust grains in the interstellar medium are known to be mostly
amorphous, yet crystalline silicate grains have been observed in many
long-period comets and in protoplanetary disks. Annealing of amorphous silicate
grains into crystalline grains requires temperatures > 1000 K, but exposure of
dust grains in comets to such high temperatures is incompatible with the
generally low temperatures experienced by comets. This has led to the proposal
of models in which dust grains were thermally processed near the protoSun, then
underwent considerable radial transport until they reached the gas giant planet
region where the long-period comets originated. We hypothesize instead that
silicate dust grains were annealed in situ, by shock waves triggered by
gravitational instabilities. We assume a shock speed of 5 km/s, a plausible
value for shocks driven by gravitational instabilities. We calculate the peak
temperatures of micron and submicron amorphous pyroxene grains of chondritic
composition under conditions typical in protoplanetary disks at 5 - 10 AU. Our
results also apply to chondritic amorphous olivine grains. We show that {\it in
situ} thermal annealing of submicron and micron-sized silicate dust grains can
occur, obviating the need for large-scale radial transport.Comment: 12 pages; includes 1 figure, 1 table; accepted by ApJ Letter
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Ceramic Component Development Process Analysis
The development of ceramic components and coatings is critical to the demonstration of advanced fossil energy systems. Ceramic components and coating will play critical role in hot-gas filtration, high- temperature heat exchangers, thermal barrier coatings, and the hot- section of turbines. Continuous-fiber composites (CFCC) are expected to play an increasing role in these applications. This program encompassed five technical areas related to ceramic component development for fossil energy systems
Toxicokinetic Profiles of α-ketoglutarate Cyanohydrin, a Cyanide Detoxification Product, Following Exposure to Potassium Cyanide
Poisoning by cyanide can be verified by analysis of the cyanide detoxification product, α-ketoglutarate cyanohydrin (α-KgCN), which is produced from the reaction of cyanide and endogenous α-ketoglutarate. Although α-KgCN can potentially be used to verify cyanide exposure, limited toxicokinetic data in cyanide-poisoned animals are available. We, therefore, studied the toxicokinetics of α-KgCN and compared its behavior to other cyanide metabolites, thiocyanate and 2-amino-2-thiazoline-4-carboxylic acid (ATCA), in the plasma of 31 Yorkshire pigs that received KCN (4 mg/mL) intravenously (IV) (0.17 mg/kg/min). α-KgCN concentrations rose rapidly during KCN administration until the onset of apnea, and then decreased over time in all groups with a half-life of 15 min. The maximum concentrations of α-KgCN and cyanide were 2.35 and 30.18 μM, respectively, suggesting that only a small fraction of the administered cyanide is converted to α-KgCN. Although this is the case, the α-KgCN concentration increased \u3e100-fold over endogenous concentrations compared to only a three-fold increase for cyanide and ATCA. The plasma profile of α-KgCN was similar to that of cyanide, ATCA, and thiocyanate. The results of this study suggest that the use of α-KgCN as a biomarker for cyanide exposure is best suited immediately following exposure for instances of acute, high-dose cyanide poisoning
Dusty Cometary Globules in W5
We report the discovery of four dusty cometary tails around low mass stars in
two young clusters belonging to the W5 star forming region. Fits to the
observed emission profiles from 24 micron observations with the Spitzer Space
Telescope give tail lifetimes < 30 Myr, but more likely < 5 Myr. This result
suggests that the cometary phase is a short lived phenomenon, occurring after
photoevaporation by a nearby O star has removed gas from the outer disk of a
young low mass star (see also Balog et al. 2006; Balog et al. 2008).Comment: 11 pages, 3 figures. Accepted for publication to ApJ Letter
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