37,761 research outputs found
Effect of Thermal Fluctuation on Spectral Function for the Tomonaga-Luttinger Model
We examine the spectral function of the single electron Green function at
finite temperatures for the Tomonaga-Luttinger model which consists of the
mutual interaction with only the forward scattering. The spectral weight, which
is calculated as a function of the frequency with the fixed wave number, shows
that several peaks originating in the excitation spectra of charge and spin
fluctuations vary into a single peak by the increase of temperature.Comment: 10 pages, 6 eps figure
Universal low-temperature properties of quantum and classical ferromagnetic chains
We identify the critical theory controlling the universal, low temperature,
macroscopic properties of both quantum and classical ferromagnetic chains. The
theory is the quantum mechanics of a single rotor. The mapping leads to an
efficient method for computing scaling functions to high accuracy.Comment: 4 pages, 2 tables and 3 Postscript figure
Abelian monopoles and center vortices in Yang-Mills plasma
Condensation of the Abelian monopoles and the center vortices leads to
confinement of color in low temperature phase of Yang-Mills theory. We stress
that these topological magnetic degrees of freedom are also very important in
the deconfinement regime: at the point of the deconfinement phase transition
both the monopoles and the vortices are released into the thermal vacuum
contributing, in particular, to the equation of state and, definitely, to
transport properties of the hot gluonic medium. Thus, we argue that a novel,
magnetic component plays a crucial role. On the other hand, it was demonstrated
that an effective three-dimensional description can be brought, beginning with
high temperatures, down to the critical temperature by postulating existence of
a system of 3d Higgs fields. We propose to identify the 3d color-singlet Higgs
field with the 3d projection of the 4d magnetic vortices. Such identification
fits well the 3d properties of the theory and contributes to interpretation of
the magnetic component of the Yang-Mills plasma.Comment: 5 pages, 3 figures; talk at Quark Confinement and the Hadron
Spectrum, September 1-6 2008, Mainz, German
Inverse Landau-Zener-Stuckelberg problem for qubit-resonator systems
We consider theoretically a superconducting qubit - nanomechanical resonator
(NR) system, which was realized by LaHaye et al. [Nature 459, 960 (2009)].
First, we study the problem where the state of the strongly driven qubit is
probed through the frequency shift of the low-frequency NR. In the case where
the coupling is capacitive, the measured quantity can be related to the
so-called quantum capacitance. Our theoretical results agree with the
experimentally observed result that, under resonant driving, the frequency
shift repeatedly changes sign. We then formulate and solve the inverse
Landau-Zener-Stuckelberg problem, where we assume the driven qubit's state to
be known (i.e. measured by some other device) and aim to find the parameters of
the qubit's Hamiltonian. In particular, for our system the qubit's bias is
defined by the NR's displacement. This may provide a tool for monitoring of the
NR's position.Comment: 10 pages, 7 figure
Some properties of the resonant state in quantum mechanics and its computation
The resonant state of the open quantum system is studied from the viewpoint
of the outgoing momentum flux. We show that the number of particles is
conserved for a resonant state, if we use an expanding volume of integration in
order to take account of the outgoing momentum flux; the number of particles
would decay exponentially in a fixed volume of integration. Moreover, we
introduce new numerical methods of treating the resonant state with the use of
the effective potential. We first give a numerical method of finding a
resonance pole in the complex energy plane. The method seeks an energy
eigenvalue iteratively. We found that our method leads to a super-convergence,
the convergence exponential with respect to the iteration step. The present
method is completely independent of commonly used complex scaling. We also give
a numerical trick for computing the time evolution of the resonant state in a
limited spatial area. Since the wave function of the resonant state is
diverging away from the scattering potential, it has been previously difficult
to follow its time evolution numerically in a finite area.Comment: 20 pages, 12 figures embedde
- …