3,943 research outputs found
Phase Structure of Repulsive Hard-Core Bosons in a Stacked Triangular Lattice
In this paper, we study phase structure of a system of hard-core bosons with
a nearest-neighbor (NN) repulsive interaction in a stacked triangular lattice.
Hamiltonian of the system contains two parameters one of which is the hopping
amplitude between NN sites and the other is the NN repulsion . We
investigate the system by means of the Monte-Carlo simulations and clarify the
low and high-temperature phase diagrams. There exist solid states with density
of boson and , superfluid, supersolid and
phase-separated state. The result is compared with the phase diagram of the
two-dimensional system in a triangular lattice at vanishing temperature.Comment: 4+epsilon pages, 11 figures, Version to be published in Phys.Rev.
Optical-lattice-assisted magnetic phase transition in a spin-orbit-coupled Bose-Einstein condensate
We investigate the effect of a periodic potential generated by a
one-dimensional optical lattice on the magnetic properties of an
spin-orbit-coupled Bose gas. By increasing the lattice strength one can achieve
a magnetic phase transition between a polarized and an unpolarized Bloch wave
phase, characterized by a significant enhancement of the contrast of the
density fringes. If the wave vector of the periodic potential is chosen close
to the roton momentum, the transition could take place at very small lattice
intensities, revealing the strong enhancement of the response of the system to
a weak density perturbation. By solving the Gross-Pitaevskii equation in the
presence of a three-dimensional trapping potential, we shed light on the
possibility of observing the magnetic phase transition in currently available
experimental conditions.Comment: 10 pages, 6 figures. Revised version, published in PR
Measuring processes and the Heisenberg picture
In this paper, we attempt to establish quantum measurement theory in the
Heisenberg picture. First, we review foundations of quantum measurement theory,
that is usually based on the Schr\"{o}dinger picture. The concept of instrument
is introduced there. Next, we define the concept of system of measurement
correlations and that of measuring process. The former is the exact counterpart
of instrument in the (generalized) Heisenberg picture. In quantum mechanical
systems, we then show a one-to-one correspondence between systems of
measurement correlations and measuring processes up to complete equivalence.
This is nothing but a unitary dilation theorem of systems of measurement
correlations. Furthermore, from the viewpoint of the statistical approach to
quantum measurement theory, we focus on the extendability of instruments to
systems of measurement correlations. It is shown that all completely positive
(CP) instruments are extended into systems of measurement correlations. Lastly,
we study the approximate realizability of CP instruments by measuring processes
within arbitrarily given error limits.Comment: v
Inverse problems of identifying the time-dependent source coefficient for subelliptic heat equations
We discuss inverse problems of determining the time-dependent source
coefficient for a general class of subelliptic heat equations. We show that a
single data at an observation point guarantees the existence of a (smooth)
solution pair for the inverse problem. Moreover, additional data at the
observation point implies an explicit formula for the time-dependent source
coefficient. We also explore an inverse problem with nonlocal additional data,
which seems a new approach even in the Laplacian case
Kinetic energy and spin-orbit splitting in nuclei near neutron drip line
Two important ingredients of nuclear shell-structure, kinetic energy and
spin-orbit splitting, are studied as a function of orbital angular momenta \ell
and binding energies, when binding energies of neutrons decrease towards zero.
If we use the standard parameters of the Woods-Saxon potential in \beta stable
nuclei and approach the limit of zero binding energy from 10 MeV, the
spin-orbit splitting for n=1 orbitals decreases considerably for \ell=1, while
for \ell > 2 little decreasing is observed in the limit. In contrast, the
kinetic energy decreases considerably for \ell \simleq 3. The smaller the \ell
values of orbitals, the larger the decreasing rate of both kinetic energy and
spin-orbit splitting. The dependence of the above bservation on the diffuseness
of potentials is studied.Comment: 12 pages, 3 figures, submitted to Nucl. Phy
Conservative Quantum Computing
Conservation laws limit the accuracy of physical implementations of
elementary quantum logic gates. If the computational basis is represented by a
component of spin and physical implementations obey the angular momentum
conservation law, any physically realizable unitary operators with size less
than n qubits cannot implement the controlled-NOT gate within the error
probability 1/(4n^2), where the size is defined as the total number of the
computational qubits and the ancilla qubits. An analogous limit for bosonic
ancillae is also obtained to show that the lower bound of the error probability
is inversely proportional to the average number of photons. Any set of
universal gates inevitably obeys a related limitation with error probability
O(1/n^2)$. To circumvent the above or related limitations yielded by
conservation laws, it is recommended that the computational basis should be
chosen as the one commuting with the additively conserved quantities.Comment: 5 pages, RevTex. Corrected to include a new statement that for
bosonic ancillae the lower bound of the error probability is inversely
proportional to the average number of photons, kindly suggested by Julio
Gea-Banacloch
Recent advances in plant early signaling in response to herbivory
Plants are frequently attacked by herbivores and pathogens and therefore have acquired constitutive and induced defenses during the course of their evolution. Here we review recent progress in the study of the early signal transduction pathways in host plants in response to herbivory. The sophisticated signaling network for plant defense responses is elicited and driven by both herbivore-induced factors (e.g., elicitors, effectors, and wounding) and plant signaling (e.g., phytohormone and plant volatiles) in response to arthropod factors. We describe significant findings, illuminating the scenario by providing broad insights into plant signaling involved in several arthropod-host interactions
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