6,515 research outputs found
On the Analysis of Chemical Composition of Moon's Surface by Direct Methods
Proportional counter for X ray emission detection and chemical analysis of lunar surface element
Isochoric thermal conductivity of solid nitrogen
The isochoric thermal conductivity of solid nitrogen has been investigated on
four samples of different densities in the temperature interval from 20 K to
the onset of melting. In alfa-N2 the isochoric thermal conductivity exhibits a
dependence weaker than 1/T; in beta-N2 it increases slightly with temperature.
The experimental results are discussed within a model in which the heat is
transported by low-frequency phonons or by "diffusive" modes above the mobility
boundary. The growth of the thermal conductivity in beta-N2 is attributed to
the decreasing "rotational" component of the total thermal resistance, which
occurs as the rotational correlations between the neighboring molecules become
weaker.Comment: Postscript 12 pages, 3 figures, 1 table. To be published in 200
Soft-Pulse Dynamical Decoupling with Markovian Decoherence
We consider the effect of broadband decoherence on the performance of
refocusing sequences, having in mind applications of dynamical decoupling in
concatenation with quantum error correcting codes as the first stage of
coherence protection. Specifically, we construct cumulant expansions of
effective decoherence operators for a qubit driven by a pulse of a generic
symmetric shape, and for several sequences of - and -pulses. While,
in general, the performance of soft pulses in decoupling sequences in the
presence of Markovian decoherence is worse than that of the ideal
-pulses, it can be substantially improved by shaping.Comment: New version contains minor content clarification
On the nonlinear NMR and magnon BEC in antiferromagnetic materials with coupled electron-nuclear spin precession
We present a new study of nonlinear NMR and Bose-Einstein Condensation (BEC)
of nuclear spin waves in antiferromagnetic MnCO3 with coupled electron and
nuclear spins. In particular, we show that the observed behaviour of NMR
signals strongly contradicts the conventional description of paramagnetic
ensembles of noninteracting spins based on the phenomenological Bloch
equations. We present a new theoretical description of the coupled
electron-nuclear spin precession, which takes into account an indirect
relaxation of nuclear spins via the electron subsystem. We show that the
magnitude of the nuclear magnetization is conserved for arbitrary large
excitation powers, which is drastically different from the conventional heating
scenario derived from the Bloch equations. This provides strong evidence that
the coherent precession of macroscopic nuclear magnetization observed
experimentally can be identified with BEC of nuclear spin waves with k=0.Comment: 12 pages, 8 figure
Normal-mode splitting in the coupled system of hybridized nuclear magnons and microwave photons
In the weak ferromagnetic MnCO system, a low-frequency collective spin
excitation (magnon) is the hybridized oscillation of nuclear and electron spins
coupled through the hyperfine interaction. By using a split-ring resonator, we
performed transmission spectroscopy measurements of MnCO system and
observed, for the first time, avoiding crossing between the hybridized
nuclear-electron magnon mode and the resonator mode in the NMR-frequency range.
The splitting strength is quite large due to the large spin density of
Mn, and the cooperativity value (magnon-photon coupling
parameter) is close to the conditions of strong coupling. The results reveal a
new class of spin systems, in which the coupling between nuclear spins and
photons is mediated by electron spins via the hyperfine interaction, and in
which the similar normal-mode splitting of the hybridized nuclear magnon mode
and the resonator mode can be observed.Comment: 5 pages, 3 figure
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