8,847 research outputs found
A New Algebraic Structure of Finite Quantum Systems and the Modified Bessel Functions
In this paper we present a new algebraic structure (a super hyperbolic system
in our terminology) for finite quantum systems, which is a generalization of
the usual one in the two-level system.
It fits into the so-called generalized Pauli matrices, so they play an
important role in the theory. Some deep relation to the modified Bessel
functions of integer order is pointed out.
By taking a skillful limit finite quantum systems become quantum mechanics on
the circle developed by Ohnuki and Kitakado.Comment: Latex ; 14 pages ; no figure ; minor changes. To appear in
International Journal of Geometric Methods in Modern Physics, (Vo.4, No.7),
200
The Kondo crossover in shot noise of a single quantum dot with orbital degeneracy
We investigate out of equilibrium transport through an orbital Kondo system
realized in a single quantum dot, described by the multiorbital impurity
Anderson model. Shot noise and current are calculated up to the third order in
bias voltage in the particle-hole symmetric case, using the renormalized
perturbation theory. The derived expressions are asymptotically exact at low
energies. The resulting Fano factor of the backscattering current is
expressed in terms of the Wilson ratio and the orbital degeneracy as
at zero temperature. Then,
for small Coulomb repulsions , we calculate the Fano factor exactly up to
terms of order , and also carry out the numerical renormalization group
calculation for intermediate in the case of two- and four-fold degeneracy
(). As increases, the charge fluctuation in the dot is suppressed,
and the Fano factor varies rapidly from the noninteracting value to the
value in the Kondo limit , near the crossover region
, with the energy scale of the hybridization .Comment: 10 pages, 4 figure
Low temperature specific heat of La_{3}Pd_{4}Ge_{4} with U_{3}Ni_{4}Si_{4}-type structure
Low temperature specific heat has been investigated in a novel ternary
superconductor La_{3}Pd_{4}Ge_{4} with an U_{3}Ni_{4}Si_{4}-type structure
consisting of the alternating BaAl_{4} (ThCr_{2}Si_{2})- and AlB-type
layers. A comparative study with the related ThCr_{2}Si_{2}-type superconductor
LaPd_{2}Ge_{2}, one of the layers in La_{3}Pd_{4}Ge_{4}, is also presented.
From the normal state specific heat, the Sommerfeld coefficient mJ/mol K^2 and the Debye temperature = 256 K are derived
for the La_{3}Pd_{4}Ge_{4}, while those for the LaPd_{2}Ge_{2} are mJ/mol K^2 and = 291 K. The La_{3}Pd_{4}Ge_{4} has
moderately high electronic density of state at the Fermi level. Electronic
contribution on the specific heat, , in each compound is well
described by the BCS behavior, suggesting that both of the La_{3}Pd_{4}Ge_{4}
and the LaPd_{2}Ge_{2} have fully opened isotropic gap in the superconducting
state
Universal Scaling Behavior of Anomalous Hall Effect and Anomalous Nernst Effect in Itinerant Ferromagnets
Anomalous Hall effect (AHE) and anomalous Nernst effect (ANE) in a variety of
ferromagnetic metals including pure metals, oxides, and chalcogenides, are
studied to obtain unified understandings of their origins. We show a universal
scaling behavior of anomalous Hall conductivity as a function of
longitudinal conductivity over five orders of magnitude, which is
well explained by a recent theory of the AHE taking into account both the
intrinsic and extrinsic contributions. ANE is closely related with AHE and
provides us with further information about the low-temperature electronic state
of itinerant ferromagnets. Temperature dependence of transverse Peltier
coefficient shows an almost similar behavior among various
ferromagnets, and this behavior is in good agreement quantitatively with that
expected from the Mott rule.Comment: 4pages, 4figures, 1tabl
Quintessence, scalar-tensor theories and non-Newtonian gravity
We discuss some of the issues which we encounter when we try to invoke the
scalar-tensor theories of gravitation as a theoretical basis of quintessence.
One of the advantages of appealing to these theories is that they allow us to
implement the scenario of a ``decaying cosmological constant,'' which offers a
reasonable understanding of why the observed upper bound of the cosmological
constant is smaller than the theoretically natural value by as much as 120
orders of magnitude. In this context, the scalar field can be a candidate of
quintessence in a broader sense. We find, however, a serious drawback in the
prototype Brans-Dicke model with added; a static universe in the
physical conformal frame which is chosen to have constant particle masses. We
propose a remedy by modifying the matter coupling of the scalar field taking
advantage of scale invariance and its breakdown through quantum anomaly. By
combining this with a conjecture on another cosmological constant problem
coming from the vacuum energy of matter fields, we expect a possible link
between quintessence and non-Newtonian gravity featuring violation of Weak
Equivalence Principle and intermediate force range, likely within the
experimental constraints. A new prediction is also offered on the
time-variability of the gravitational constant.Comment: 12 pages LaTex including 1 eps figur
Enhancement of Superconducting Transition Temperature due to the strong Antiferromagnetic Spin Fluctuations in Non-centrosymmetric Heavy-fermion Superconductor CeIrSi3 :A 29Si-NMR Study under Pressure
We report a 29Si-NMR study on the pressure-induced superconductivity (SC) in
an antiferromagnetic (AFM) heavy-fermion compound CeIrSi3 without inversion
symmetry. In the SC state at P=2.7-2.8 GPa, the temperature dependence of the
nuclear-spin lattice relaxation rate 1/T_1 below Tc exhibits a T^3 behavior
without any coherence peak just below Tc, revealing the presence of line nodes
in the SC gap. In the normal state, 1/T_1 follows a \sqrt{T}-like behavior,
suggesting that the SC emerges under the non-Fermi liquid state dominated by
AFM spin fluctuations enhanced around quantum critical point (QCP). The reason
why the maximum Tc in CeIrSi3 is relatively high among the Ce-based
heavy-fermion superconductors may be the existence of the strong AFM spin
fluctuations. We discuss the comparison with the other Ce-based heavy-fermion
superconductors.Comment: 4 pages, 5 figures, To be published in Phys. Rev. Let
Cavity QED and Quantum Computation in the Weak Coupling Regime
In this paper we consider a model of quantum computation based on n atoms of
laser-cooled and trapped linearly in a cavity and realize it as the n atoms
Tavis-Cummings Hamiltonian interacting with n external (laser) fields.
We solve the Schr{\" o}dinger equation of the model in the case of n=2 and
construct the controlled NOT gate by making use of a resonance condition and
rotating wave approximation associated to it. Our method is not heuristic but
completely mathematical, and the significant feature is a consistent use of
Rabi oscillations.
We also present an idea of the construction of three controlled NOT gates in
the case of n=3 which gives the controlled-controlled NOT gate.Comment: Latex file, 22 pages, revised version. To appear in Journal of Optics
B : Quantum and Semiclassical Optic
Stability and Representation Dependence of the Quantum Skyrmion
A constructive realization of Skyrme's conjecture that an effective pion mass
``may arise as a self consistent quantal effect'' based on an ab initio quantum
treatment of the Skyrme model is presented. In this quantum mechanical Skyrme
model the spectrum of states with , which appears in the collective
quantization, terminates without any infinite tower of unphysical states. The
termination point depends on the model parameters and the dimension of the
SU(2) representation. Representations, in which the nucleon and
resonance are the only stable states, exist. The model is developed for both
irreducible and reducible representations of general dimension. States with
spin larger than 1/2 are shown to be deformed. The representation dependence of
the baryon observables is illustrated numerically.Comment: 19 pages, Late
Determination of the local structure of SrMIrO (M = K, La) as a function of doping and temperature
The local structure of correlated spin-orbit insulator SrMIrO
(M = K, La) has been investigated by Ir L-edge extended x-ray absorption
fine structure measurements. The measurements were performed as a function of
temperature for different dopings induced by substitution of Sr with La or K.
It is found that Ir-O bonds have strong covalency and they hardly show any
change across the N\'eel temperature. In the studied doping range, neither Ir-O
bonds nor their dynamics, measured by their mean square relative displacements,
show any appreciable change upon carrier doping, indicating possibility of a
nanoscale phase separation in the doped system. On the other hand, there is a
large increase of the static disorder in Ir-Sr correlation, larger for K doping
than La doping. Similarities and differences with respect to the local lattice
displacements in cuprates are briefly discussed.Comment: Main text: 6 pages, 4 figures, Supplemental information: 2 pages, 2
figure
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