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The 15-metre-long, extinct megalodon shark (Otodus megalodon) may have been higher up the food chain than any living marine predator, meaning it hunted other predators. The finding comes from an analysis of nitrogen isotopes in the shark's fossilised teeth (Science Advances, doi.org/gqc8kv). [Extracted from the article]

We describe a collective state atomic clock (COSAC) with Ramsey fringes narrowed by a factor of √N compared to a conventional clock--N being the number of noninteracting atoms--without violating the uncertainty relation. This narrowing is explained as being due to interferences among the collective states, representing an effective √N-fold increase in the clock frequency, without entanglement. We discuss the experimental inhomogeneities that affect the signal and show that experimental parameters can be adjusted to produce a near ideal signal. The detection process collects fluorescence through stimulated Raman scattering of Stokes photons, which emits photons predominantly in the direction of the probe beam for a high enough optical density. By using a null measurement scheme, in which detection of zero photons corresponds to the system being in a single collective state, we detect the population in a collective state of interest. The quantum and classical noise of the ideal COSAC is still limited by the standard quantum limit and performs only as well as the conventional clock. However, when detection efficiency and collection efficiency are taken into account, the detection scheme of the COSAC increases the quantum efficiency of detection significantly in comparison to a typical conventional clock employing fluorescence detection, yielding a net improvement in stability by as much as a factor of 10. [ABSTRACT FROM AUTHOR]

A negatively charged nitrogen-vacancy (NV) center in diamond has been recognized as a good solid-state qubit. A system consisting of the electronic spin of the NV center and hyperfine-coupled nitrogen and additionally nearby carbon nuclear spins can form a quantum register of several qubits for quantum information processing or as a node in a quantum repeater. Several impressive experiments on the hybrid electron and nuclear spin register have been reported, but fidelities achieved so far are not yet at or below the thresholds required for fault-tolerant quantum computation (FTQC). Using quantum optimal control theory based on the Krotov method, we show here that fast and high-fidelity single-qubit and two-qubit gates in the universal quantum gate set for FTQC, taking into account the effects of the leakage state, nearby noise qubits, and distant bath spins, can be achieved with errors less than those required by the threshold theorem of FTQC. [ABSTRACT FROM AUTHOR]

The high-order-harmonic generation (HHG) from the N2 molecule in an intense laser field is investigated by applying the Lewenstein method. The initial state is constructed as a linear combination of the highest occupied molecular orbital (HOMO) and the lower-lying orbital below the HOMO, which is well described by a Gaussian wave packet generated by using the GAMESS-UK package. The HHG with different vibrational states of N2 are calculated and our results show that the harmonic intensity can be enhanced by higher vibrational states, which can be explained by the ionization probability. We also compared the cases with a different full width at half maximum of laser fields together, which can be well understood by the time-frequency analysis and the three-step model. Finally, the attosecond pulse generation is studied with different vibrational states, where a series of attosecond pulses can be produced with the shortest being 91 as. [ABSTRACT FROM AUTHOR]

The electron loss to the continuum has been studied for the collision system U88+ + N2 → U89+ + [N2]* + e- at the low-relativistic projectile energy of 90 MeV/u. Using a magnetic electron spectrometer, the energy distribution of cusp electrons emitted at an angle of 0° with respect to the projectile beam was measured in coincidence with the up-charged projectile. At the experimental collision energy ionization of the berylliumlike U88+ projectile proceeds predominantly from the L shell, but a contribution from the K shell could also be identified experimentally. The measurement is shown to be in accordance with fully relativistic Dirac calculations applying first-order perturbation theory. Furthermore, the underlying continuum electron distribution in the projectile frame is illustrated. [ABSTRACT FROM AUTHOR]

We report on experimental and theoretical investigations of dynamic evolution of individual /f-branch laser lines from tunnel-ionized nitrogen molecules based on a pump-probe scheme. Our observation shows that the intensities of the R-branch laser lines exhibit rapid oscillations which can be decomposed into periodic oscillations at different frequencies. The oscillations can be attributed to the coupling between the rotational quantum states mediated either by the probe pulses or by the P-branch laser emission from the molecular ions. [ABSTRACT FROM AUTHOR]

We show how nitrogen-vacancy centers can be used to determine the amplitude, phase, and frequency of unknown weak monochromatic and multichromatic oscillating magnetic fields using only the periodic dynamical decoupling and Carr-Purcell-Meiboom-Gill sequences. The effect of decoherence on the measurement of the magnetic field parameters is explicitly analyzed, and we take into account the fact that different pulse sequences suppress decoherence to different extents. Since the sensitivity increases with increasing sensing time while it decreases due to decoherence and limited photon detection efficiency, we use the Fisher information matrix in order to optimize the number of pulses that should be used. [ABSTRACT FROM AUTHOR]

The article evaluates the Dumatherm and Kjeldatherm and Turbotherm digestion systems for nitrogen determination from C. Gerhardt.

In lots of situations, the ideal energy storage device is not a battery, which stores lots of energy but can't deliver it particularly quickly. Nor is it a supercapacitor, which has limited storage but delivers what it's got quickly. Instead it would be something that could do both. Scientists in China and the United States recently took a big step toward that ideal component when they showed that nitrogen can triple the energy storage capacity of carbon-based supercapacitors, potentially making them competitive with some batteries in terms of the amount of energy stored. [ABSTRACT FROM PUBLISHER]