646 research outputs found
Problems with interpretation of He ground state
The continuum of He nucleus is studied theoretically in a three-body
He++ model basing on the recent information concerning He
spectrum [Golovkov, \textit{et al.}, Phys. Rev. C \textbf{76}, 021605(R)
(2007)]. The He ground state (g.s.) candidate with structure
for new g.s. energy of He is predicted to be at about
MeV. The peak in the cross section associated with this state may be
shifted to a lower energy (e.g. MeV) when He is populated in
reactions with Li due to peculiar reaction mechanism. Formation of the
low-energy ( keV) ``alternative'' ground state with structure
is highly probable in He in the case of considerable
attraction (e.g. fm) in the s-wave He channel, which properties are
still quite uncertain. This result either questions the existing experimental
low-energy spectrum of He or place a limit on the scattering length in
He channel, which contradicts existing data.Comment: 14 pages, 13 figures, 1 tabl
Accurate "superluminal" transmission via entanglement, superoscillations and quasi-Dirac distributions
We analyse a system in which, due to entanglement between the spin and
spatial degrees of freedom, the reduced transmitted state has the shape of the
freely propagating pulse translated in the complex co-ordinate plane. In the
case an apparently "superluminal" advancement of the pulse the delay amplitude
distribution is found to be a peculiar approximation to the Dirac
delta-function, and the transmission coefficient exhibits a well-defined
super-oscillatory window. Analogies with potential tunnelling and the Wheeler's
delayed choice experiment are highlighted
Threshold Effects in Multi-channel Coupling and Spectroscopic Factors in Exotic Nuclei
In the threshold region, the cross section and the associated overlap
integral obey the Wigner threshold law that results in the Wigner-cusp
phenomenon. Due to flux conservation, a cusp anomaly in one channel manifests
itself in other open channels, even if their respective thresholds appear at a
different energy. The shape of a threshold cusp depends on the orbital angular
momentum of a scattered particle; hence, studies of Wigner anomalies in weakly
bound nuclei with several low-lying thresholds can provide valuable
spectroscopic information. In this work, we investigate the threshold behavior
of spectroscopic factors in neutron-rich drip-line nuclei using the Gamow Shell
Model, which takes into account many-body correlations and the continuum
effects. The presence of threshold anomalies is demonstrated and the
implications for spectroscopic factors are discussed.Comment: Accepted in Physical Review C Figure correcte
Qubit residence time measurements with a Bose-Einstein condensate
We show that an electrostatic qubit located near a Bose-Einstein condensate
trapped in a symmetric double-well potential can be used to measure the
duration the qubit has spent in one of its quantum states. The stronq, medium
and weak measurement regimes are analysed and a new type of Zeno effect is
discussed. The analogy between the residence and the traversal (tunnelling)
times is highlighted
The -matrix inverse scattering approach for coupled channels with different thresholds
The inverse scattering method within the -matrix approach to the two
coupled-channel problem is discussed. We propose a generalization of the
procedure to the case with different thresholds.Comment: 20 pages, 3 figure
Hartman effect and spin precession in graphene
Spin precession has been used to measure the transmission time \tau over a
distance L in a graphene sheet. Since conduction electrons in graphene have an
energy-independent velocity v, one would expect \tau > L/v. Here we calculate
that \tau < L/v at the Dirac point (= charge neutrality point) in a clean
graphene sheet, and we interpret this result as a manifestation of the Hartman
effect (apparent superluminality) known from optics.Comment: 6 pages, 4 figures; v2: added a section on the case of
perpendicularly aligned magnetizations; v3: added a figur
Entanglement entropy in Fermi gases and Anderson's orthogonality catastrophe
We study the ground-state entanglement entropy of a finite subsystem of size L of an infinite system of noninteracting fermions scattered by a potential of finite range a. We derive a general relation between the scattering matrix and the overlap matrix and use it to prove that for a one-dimensional symmetric potential the von Neumann entropy, the Rényi entropies, and the full counting statistics are robust against potential scattering, provided that L/a≫1. The results of numerical calculations support the validity of this conclusion for a generic potential
Compact and Loosely Bound Structures in Light Nuclei
A role of different components in the wave function of the weakly bound light
nuclei states was studied within the framework of the cluster model, taking
into account of orbitals "polarization". It was shown that a limited number of
structures associated with the different modes of nucleon motion can be of
great importance for such systems. Examples of simple and quite flexible trial
wave functions are given for the nuclei Be, He. Expressions for the
microscopic wave functions of these nuclei were found and used for the
calculation of basic nuclear characteristics, using well known central-exchange
nucleon-nucleon potentials.Comment: 19 pages, 3 ps figure
Resonances in one-dimensional Disordered Chain
We study the average density of resonances, is
defined in the complex energy plane and the distance from the real axes
determines the resonance width. We concentrate on strong disorder and derive
the asymptotic behavior of in the limit of small .Comment: latex, 1 eps figure, 9 pages; v2 - final version, published in the
JPhysA Special Issue Dedicated to the Physics of Non-Hermitian Operator
Traversal time for electron tunneling in water
The traversal time for tunneling is a measure of the time during which the
transmitted particle can be affected by interactions localized in the barrier.
The Buttiker-Landauer approach, which estimates this time by imposing an
internal clock on the system, has been applied so far for relatively simple
1-dimensional models. Here we apply this approach to estimate the traversal
time for electron tunneling through a realistic 3-dimensional model of a water
layer. Observed structure in the energy dependence of times computed reflects
the existence of transient tunneling resonances associated with instantaneous
water structures.Comment: 9 pages, 3 figures. Submitted to the Journal of Chemical Physic
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