477 research outputs found
A fresh look on the flux tube in Abelian-projected SU(2) gluodynamics
We reconsider the properties of the flux tube within
Abelian-projected SU(2) lattice gauge theory in terms of electric field and
monopole current. In the maximal Abelian gauge we assess the influence of the
Gribov copies on the apparent flux-tube profile. For the optimal gauge fixing
we study the independence of the profile on the lattice spacing for
2.3, 2.4, and 2.5115 on a lattice. We decompose the Abelian Wilson loop
into monopole and photon parts and compare the electric and monopole profile
emerging from different sources with the field strength and monopole current
within the dual Ginzburg-Landau theory.Comment: 3 pages, 6 figures, Lattice2002(topology
Effective string action for the U(1)xU(1) dual Ginzburg-Landau theory beyond the London limit
The effective string action of the color-electric flux tube in the U(1) x
U(1) dual Ginzburg-Landau (DGL) theory is studied by performing a path-integral
analysis by taking into accountthe finite thickness of the flux tube. The DGL
theory, corresponding to the low-energy effective theory of Abelian-projected
SU(3) gluodynamics, can be expressed as s [U(1)]^{3} dual Abelian Higgs (DAH)
model with a certain constraint in the Weyl symmetric formulation. This
formulation allows us to adopt quite similar path-integral techniques as in the
U(1) DAH model, and therefore, the resulting effective string action in the
U(1) x U(1) DGL theory has also quite a similar structure except the number of
color degrees of freedom. A modified Yukawa interaction appears as a boundary
contribution, which is completely due to the finite thickness of the flux tube,
and is reduced into the ordinary Yukawa interaction in the deep type-II
(London) Limit.Comment: 17 pages, 1 eps figure, The version accepted for publication in Nucl.
Phys.
Density matrix for the kink ground state of the ferromagnetic XXZ chain
The exact expression for the density matrix of the kink ground state of the
ferromagnetic XXZ chain is obtained. Utilizing this, we exactly calculate
various correlation functions such as the longitudinal and transverse spin-spin
correlation functions, and the ferromagnetic and antiferromagnetic string
formation probabilities. The asymptotic behaviors of these correlation
functions are also analyzed. As a consequence, we find that the spin-spin
correlation functions decay exponentially for large distances, while the string
formation probabilities exhibit Gaussian decay for large strings. We also
evaluate the entanglement entropy, which shows interesting behaviors due to the
lack of the translational invariance of the state.Comment: 7 pages, 9 figure
Isolated Eigenvalues of the Ferromagnetic Spin-J XXZ Chain with Kink Boundary Conditions
We investigate the low-lying excited states of the spin J ferromagnetic XXZ
chain with Ising anisotropy Delta and kink boundary conditions. Since the third
component of the total magnetization, M, is conserved, it is meaningful to
study the spectrum for each fixed value of M. We prove that for J>= 3/2 the
lowest excited eigenvalues are separated by a gap from the rest of the
spectrum, uniformly in the length of the chain. In the thermodynamic limit,
this means that there are a positive number of excitations above the ground
state and below the essential spectrum
Implementing Quantum Gates using the Ferromagnetic Spin-J XXZ Chain with Kink Boundary Conditions
We demonstrate an implementation scheme for constructing quantum gates using
unitary evolutions of the one-dimensional spin-J ferromagnetic XXZ chain. We
present numerical results based on simulations of the chain using the
time-dependent DMRG method and techniques from optimal control theory. Using
only a few control parameters, we find that it is possible to implement one-
and two-qubit gates on a system of spin-3/2 XXZ chains, such as Not, Hadamard,
Pi-8, Phase, and C-Not, with fidelity levels exceeding 99%.Comment: Updated Acknowledgement
Towards the String representation of the dual Abelian Higgs model beyond the London limit
We perform a path-integral analysis of the string representation of the dual
Abelian Higgs (DAH) model beyond the London limit, where the string describing
the vortex of a flux tube has a finite thickness. We show that besides an
additional vortex core contribution to the string tension, a modified Yukawa
interaction appears as a boundary contribution in the type-II dual
superconducting vacuum. In the London limit, the modified Yukawa interaction is
reduced to the Yukawa one.Comment: 13 pages, JHEP3.cls is used, no figures. The version accepted for
publication in JHE
Stability of quantum states of finite macroscopic systems against classical noises, perturbations from environments, and local measurements
We study the stability of quantum states of macroscopic systems of finite
volume V, against weak classical noises (WCNs), weak perturbations from
environments (WPEs), and local measurements (LMs). We say that a pure state is
`fragile' if its decoherence rate is anomalously great, and `stable against
LMs' if the result of a LM is not affected by another LM at a distant point. By
making full use of the locality and huge degrees of freedom, we show the
following: (i) If square fluctuation of every additive operator is O(V) or less
for a pure state, then it is not fragile in any WCNs or WPEs. (ii) If square
fluctuations of some additive operators are O(V^2) for a pure state, then it is
fragile in some WCNs or WPEs. (iii) If a state (pure or mixed) has the `cluster
property,' then it is stable against LMs, and vice versa. These results have
many applications, among which we discuss the mechanism of symmetry breaking in
finite systems.Comment: 6 pages, no figure.Proof of the theorem is described in the revised
manuscrip
- …