34,366 research outputs found
Comment on "Bounding and approximating parabolas for the spectrum of Heisenberg spin systems" by Schmidt, Schnack and Luban
Recently, Schmidt et al. proved that the energy spectrum of a Heisenberg spin
system (HSS) is bounded by two parabolas, i.e. lines which depend on the total
spin quantum number S as S(S+1). The prove holds for homonuclear HSSs which
fulfill a weak homogenity condition. Moreover, the extremal values of the exact
spectrum of various HSS which were studied numerically were found to lie on
approximate parabolas, named rotational bands, which could be obtained by a
shift of the boundary parabolas. In view of this, it has been claimed that the
rotational band structure (RBS) of the energy spectrum is a general behavior of
HSSs. Furthermore, since the approximate parabolas are very close to the true
boundaries of the spectrum for the examples discussed, it has been claimed that
the methods allow to predict the detailed shape of the spectrum and related
properties for a general HSS. In this comment I will show by means of examples
that the RBS hypothesis is not valid for general HSSs. In particular, weak
homogenity is neither a necessary nor a sufficient condition for a HSS to
exhibit a spectrum with RBS.Comment: Comments on the work of Schmidt et al, Europhys. Lett. 55, 105
(2001), cond-mat/0101228 (for the reply see cond-mat/0111581). To be
published in Europhys. Let
Initiating the effective unification of black hole horizon area and entropy quantization with quasi-normal modes
Black hole (BH) quantization may be the key to unlocking a unifying theory of
quantum gravity (QG). Surmounting evidence in the field of BH research
continues to support a horizon (surface) area with a discrete and uniformly
spaced spectrum, but there is still no general agreement on the level spacing.
In this specialized and important BH case study, our objective is to report and
examine the pertinent groundbreaking work of the strictly thermal and
non-strictly thermal spectrum level spacing of the BH horizon area quantization
with included entropy calculations, which aims to tackle this gigantic problem.
In particular, this work exemplifies a series of imperative corrections that
eventually permits a BH's horizon area spectrum to be generalized from strictly
thermal to non-strictly thermal with entropy results, thereby capturing
multiple preceding developments by launching an effective unification between
them. Moreover, the identified results are significant because quasi-normal
modes (QNM) and "effective states" characterize the transitions between the
established levels of the non-strictly thermal spectrum.Comment: 23 pages, review paper. Final version to appear in Advances in High
Energy Physic
Deconstructing (2,0) proposals
C. P. is supported by the U.S. Department of Energy under
Grant No. DE-FG02-96ER40959. M. S. S. is supported by
an EURYI award of the European Science Foundatio
Precision isotope shift measurements in Ca using highly sensitive detection schemes
We demonstrate an efficient high-precision optical spectroscopy technique for
single trapped ions with non-closed transitions. In a double-shelving
technique, the absorption of a single photon is first amplified to several
phonons of a normal motional mode shared with a co-trapped cooling ion of a
different species, before being further amplified to thousands of fluorescence
photons emitted by the cooling ion using the standard electron shelving
technique. We employ this extension of the photon recoil spectroscopy technique
to perform the first high precision absolute frequency measurement of the
D P transition in Ca,
resulting in a transition frequency of kHz.
Furthermore, we determine the isotope shift of this transition and the
S P transition for Ca,
Ca and Ca ions relative to Ca with an
accuracy below 100 kHz. Improved field and mass shift constants of these
transitions as well as changes in mean square nuclear charge radii are
extracted from this high resolution data
SiGe quantum dots for fast hole spin Rabi oscillations
We report on hole g-factor measurements in three terminal SiGe self-assembled
quantum dot devices with a top gate electrode positioned very close to the
nanostructure. Measurements of both the perpendicular as well as the parallel
g-factor reveal significant changes for a small modulation of the top gate
voltage. From the observed modulations we estimate that, for realistic
experimental conditions, hole spins can be electrically manipulated with Rabi
frequencies in the order of 100MHz. This work emphasises the potential of
hole-based nano-devices for efficient spin manipulation by means of the
g-tensor modulation technique
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