56,053 research outputs found

### Combined effect of frustration and dimerization in ferrimagnetic chains and square lattice

Within the zero-temperature linear spin-wave theory we have investigated the
effect of frustration and dimerization of a Heisenberg system with alternating
spins $s_{1}$ and $s_{2}$ on one- and two-dimensional lattices. The combined
effect most visibly appears in the elementary excitation spectra. In contrast
to the ground state energy that decreases with dimerization and increases with
frustration, the excitation energies are shown to be suppressed in energy by
both dimerization and frustration. The threshold value of frustration that
signals a transition from a classical ferrimagnetic state to a spiral state,
decreases with dimerization, showing that dimerization further helps in the
phase transition. The correlation length and sublattice magnetization decrease
with both dimerization and frustration indicating the destruction of the
long-range classical ferrimagnetic. The linear spin wave theory shows that in
the case of a square lattice, dimerization initially opposes the
frustration-led transition to a spiral magnetic state, but then higher
magnitudes of lattice deformation facilitate the transition. It also shows that
the transition to spiral state is inhibited in a square lattice beyond a
certain value of dimerization.Comment: 8 pages, latex, 12 postscript figure

### Intrinsic double-peak structure of the specific heat in low-dimensional quantum ferrimagnets

Motivated by recent magnetic measurements on A3Cu3(PO4)4 (A=Ca,Sr) and
Cu(3-Clpy)2(N3)2 (3-Clpy=3-Chloropyridine), both of which behave like
one-dimensional ferrimagnets, we extensively investigate the ferrimagnetic
specific heat with particular emphasis on its double-peak structure. Developing
a modified spin-wave theory, we reveal that ferromagnetic and antiferromagnetic
dual features of ferrimagnets may potentially induce an extra low-temperature
peak as well as a Schottky-type peak at mid temperatures in the specific heat.Comment: 5 pages, 6 figures embedded, Phys. Rev. B 65, 214418 (2002

### Parametrization of the feedback Hamiltonian realizing a pure steady state

Feedback control is expected to considerably protect quantum states against
decoherence caused by interaction between the system and environment.
Especially, Markovian feedback scheme developed by Wiseman can modify the
properties of decoherence and eventually recover the purity of the steadystate
of the corresponding master equation. This paper provides a condition for which
the modified master equation has a pure steady state. By applying this
condition to a two-qubit system, we obtain a complete parametrization of the
feedback Hamiltonian such that the steady state becomes a maximally entangled
state.Comment: 4 page

### Nuclear Spin-Lattice Relaxation in One-Dimensional Heisenberg Ferrimagnets: Three-Magnon versus Raman Processes

Nuclear spin-lattice relaxation in one-dimensional Heisenberg ferrimagnets is
studied by means of a modified spin-wave theory. We consider the second-order
process, where a nuclear spin flip induces virtual spin waves which are then
scattered thermally via the four-magnon exchange interaction, as well as the
first-order process, where a nuclear spin directly interacts with spin waves
via the hyperfine interaction. We point out a possibility of the three-magnon
relaxation process predominating over the Raman one and suggest model
experiments.Comment: to be published in J. Phys. Soc. Jpn. 73, No. 6 (2004

### Relevant gluonic energy scale of spontaneous chiral symmetry breaking from lattice QCD

We analyze which momentum component of the gluon field induces spontaneous
chiral symmetry breaking in lattice QCD. After removing the high-momentum or
low-momentum component of the gluon field, we calculate the chiral condensate
and observe the roles of these momentum components. The chiral condensate is
found to be drastically reduced by removing the zero-momentum gluon. The
reduction is about 40% of the total in our calculation condition. The
nonzero-momentum infrared gluon also has a sizable contribution to the chiral
condensate. From the Banks-Casher relation, this result reflects the nontrivial
relation between the infrared gluon and the zero-mode quark

### Majorana-Like Modes of Light in a One-Dimensional Array of Nonlinear Cavities

The search for Majorana fermions in p-wave paired fermionic systems has
recently moved to the forefront of condensed-matter research. Here we propose
an alternative route and show theoretically that Majorana-like modes can be
realized and probed in a driven-dissipative system of strongly correlated
photons consisting of a chain of tunnel-coupled cavities, where p-wave pairing
effectively arises from the interplay between strong on-site interactions and
two-photon parametric driving. The nonlocal nature of these exotic modes could
be demonstrated through cross-correlation measurements carried out at the ends
of the chain---revealing a strong photon bunching signature---and their
non-Abelian properties could be simulated through tunnel-braid operations.Comment: 5 pages, 2 figures; with Supplemental Material (12 pages

### Certifying isolated singular points and their multiplicity structure

This paper presents two new constructions related to singular solutions of
polynomial systems. The first is a new deflation method for an isolated
singular root. This construc-tion uses a single linear differential form
defined from the Jacobian matrix of the input, and defines the deflated system
by applying this differential form to the original system. The advantages of
this new deflation is that it does not introduce new variables and the increase
in the number of equations is linear instead of the quadratic increase of
previous methods. The second construction gives the coefficients of the
so-called inverse system or dual basis, which defines the multiplicity
structure at the singular root. We present a system of equations in the
original variables plus a relatively small number of new vari-ables. We show
that the roots of this new system include the original singular root but now
with multiplicity one, and the new variables uniquely determine the
multiplicity structure. Both constructions are "exact", meaning that they
permit one to treat all conjugate roots simultaneously and can be used in
certification procedures for singular roots and their multiplicity structure
with respect to an exact rational polynomial system

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