397 research outputs found
A Continuous Non-demolition Measurement of the Cs Clock Transition Pseudo-spin
We demonstrate a weak continuous measurement of the pseudo-spin associated
with the clock transition in a sample of Cs atoms. Our scheme uses an optical
probe tuned near the D1 transition to measure the sample birefringence, which
depends on the z-component of the collective pseudospin. At certain probe
frequencies the differential light shift of the clock states vanishes and the
measurement is non-perturbing. In dense samples the measurement can be used to
squeeze the collective clock pseudo-spin, and has potential to improve the
performance of atomic clocks and interferometers.Comment: 4 pages, 4 figures, ReVTeX, modified text in response to referee's
comment
Inequalities of wealth distribution in a conservative economy
We analyze a conservative market model for the competition among economic
agents in a close society. A minimum dynamics ensures that the poorest agent
has a chance to improve its economic welfare. After a transient, the system
self-organizes into a critical state where the wealth distribution have a
minimum threshold, with almost no agent below this poverty line, also, very few
extremely rich agents are stable in time. Above the poverty line the
distribution follows an exponential behavior. The local solution exhibits a low
Gini index, while the mean field solution of the model generates a wealth
distribution similar to welfare states like Sweden.Comment: 7 pages, 4 figures, submitted to Physica A, Proceedings of the VIII
LAWNP, Salvador, Brazil, 200
Effect of disorder on the far-infrared conductivity and on the microwave conductivity of two-band superconductors
We consider the far-infrared and the microwave conductivities of a two-band
superconductor with non-magnetic impurities. The strong coupling expressions
for the frequency and temperature dependent conductivity of a two-band
superconductor are developed assuming isotropic bands and interactions. Our
numerical results obtained using realistic interaction parameters for MgB
are compared with experiments on this compound. We find that the available
experimental results for the far-infrared conductivity of MgB are
consistent with multi-band superconductivity in the presence of a sufficiently
strong interband impurity scattering. On the other hand, our numerical results
for the microwave conductivity in the superconducting state indicate that the
experimental results obtained on samples with the highest transition
temperature are consistent with a low interband impurity scattering
rate but depend sensitively on the ratio of the total scattering rates in the
two bands. For the -band scattering rate not greater than
the -band scattering rate there is a single, broad,
low-temperature (at about 0.5) coherence peak in the microwave
conductivity. For =4--7 a high-temperature (at
about 0.9) coherence peak is dominant, but there is also a
low-temperature peak/shoulder resulting from the contribution of the -band
carriers to the microwave conductivity. For 1
only the high-temperature coherence peak should be observable.Comment: 11 pages, 6 figure
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