168,069 research outputs found
Sub-femtotesla scalar atomic magnetometer using multipass cells
Scalar atomic magnetometers have many attractive features but their
sensitivity has been relatively poor. We describe a Rb scalar gradiometer using
two multi-pass optical cells. We use a pump-probe measurement scheme to
suppress spin-exchange relaxation and two probe pulses to find the spin
precession zero crossing times with a resolution of 1 psec. We realize magnetic
field sensitivity of 0.54 fT/Hz, which improves by an order of
magnitude the best scalar magnetometer sensitivity and surpasses the quantum
limit set by spin-exchange collisions for a scalar magnetometer with the same
measurement volume operating in a continuous regime.Comment: 5 pages, 4 figure
Comment on "The Tropospheric Land-Sea Warming Contrast as the Driver of Tropical Sea Level Pressure Changes" by Bayr and Dommenget
T Bayr and D Dommenget [J. Climate 26 (2013) 1387] proposed a model of
temperature-driven air redistribution to quantify the ratio between changes of
sea level pressure and mean tropospheric temperature in the
tropics. This model assumes that the height of the tropical troposphere is
isobaric. Here problems with this model are identified. A revised relationship
between and is derived governed by two parameters -- the isobaric
and isothermal heights -- rather than just one. Further insight is provided by
the model of R S Lindzen and S Nigam [J. Atmos. Sci. 44 (1987) 2418], which was
the first to use the concept of isobaric height to relate tropical to air
temperature, and did this by assuming that isobaric height is always around 3
km and isothermal height is likewise near constant. Observational data,
presented here, show that neither of these heights is spatially universal nor
do their mean values match previous assumptions. Analyses show that the ratio
of the long-term changes in and associated with land-sea
temperature contrasts in a warming climate -- the focus of Bayr and Dommenget
[2013] -- is in fact determined by the corresponding ratio of spatial
differences in the annual mean and . The latter ratio, reflecting
lower pressure at higher temperature in the tropics, is dominated by meridional
pressure and temperature differences rather than by land-sea contrasts.
Considerations of isobaric heights are shown to be unable to predict either
spatial or temporal variation in . As noted by Bayr and Dommenget [2013],
the role of moisture dynamics in generating sea level pressure variation
remains in need of further theoretical investigations.Comment: 26 pages, 11 figures. arXiv admin note: text overlap with
arXiv:1404.101
SLOCC determinant invariants of order 2^{n/2} for even n qubits
In this paper, we study SLOCC determinant invariants of order 2^{n/2} for any
even n qubits which satisfy the SLOCC determinant equations. The determinant
invariants can be constructed by a simple method and the set of all these
determinant invariants is complete with respect to permutations of qubits.
SLOCC entanglement classification can be achieved via the vanishing or not of
the determinant invariants. We exemplify the method for several even number of
qubits, with an emphasis on six qubits.Comment: J. Phys. A: Math. Theor. 45 (2012) 07530
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