797 research outputs found
Geometric phase of a two-level system in a dissipative environment
The geometric (Berry) phase of a two-level system in a dissipative
environment is analyzed by using the second-quantized formulation, which
provides a unified and gauge-invariant treatment of adiabatic and nonadiabatic
phases and is thus applicable to a quantitative analysis of transitional
regions away from ideal adiabaticity. In view of the recent experimental
observation of the Berry phase in a superconducting qubit, we illustrate our
formulation for a concrete adiabatic case in the Ohmic dissipation. The
correction to the total phase together with the geometry-dependent dephasing
time is given in a transparent way. The behavior of the geometric phase away
from ideal adiabaticity is also analyzed in some detail.Comment: 7 pages, 3 figure
Low energy exciton states in a nanoscopic semiconducting ring
We consider an effective mass model for an electron-hole pair in a simplified
confinement potential, which is applicable to both a nanoscopic self-assembled
semiconducting InAs ring and a quantum dot. The linear optical susceptibility,
proportional to the absorption intensity of near-infrared transmission, is
calculated as a function of the ring radius . Compared with the
properties of the quantum dot corresponding to the model with a very small
radius , our results are in qualitative agreement with the recent
experimental measurements by Pettersson {\it et al}.Comment: 4 pages, 4 figures, revised and accepted by Phys. Rev.
Mesoscopic Kondo screening effect in a single-electron transistor embedded in a metallic ring
We study the Kondo screening effect generated by a single-electron transistor
or quantum dot embedded in a small metallic ring. When the ring circumference
becomes comparable to the fundamental length scale associated with the {\it bulk} Kondo tempe the Kondo resonance is
strongly affected, depending on the total number of electrons ({\it modulo} 4)
and magnetic flux threading the ring. The resulting Kondo-assisted persistent
currents are also calculated in both Kondo and mixed valence regimes, and the
maximum values are found in the crossover region.Comment: 4 pages, Revtex, 6 figures, more references are include
Valence bond spin liquid state in two-dimensional frustrated spin-1/2 Heisenberg antiferromagnets
Fermionic valence bond approach in terms of SU(4) representation is proposed
to describe the frustrated Heisenberg antiferromagnetic (AF)
model on a {\it bipartite} square lattice. A uniform mean field solution
without breaking the translational and rotational symmetries describes a
valence bond spin liquid state, interpolating the two different AF ordered
states in the large and large limits, respectively. This novel
spin liquid state is gapless with the vanishing density of states at the Fermi
nodal points. Moreover, a sharp resonance peak in the dynamic structure factor
is predicted for momenta and in the strongly
frustrated limit , which can be checked by neutron
scattering experiment.Comment: Revtex file, 4 pages, 4 figure
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