3,408 research outputs found
Force Chain Evolution in a Two-Dimensional Granular Packing Compacted by Vertical Tappings
We experimentally study the statistics of force-chain evolution in a
vertically-tapped two-dimensional granular packing by using photoelastic disks.
In this experiment, the tapped granular packing is gradually compacted. During
the compaction, the isotropy of grain configurations is quantified by measuring
the deviator anisotropy derived from fabric tensor, and then the evolution of
force-chain structure is quantified by measuring the interparticle forces and
force-chain orientational order parameter. As packing fraction increases, the
interparticle force increases and finally saturates to an asymptotic value.
Moreover, the grain configurations and force-chain structures become
isotropically random as the tapping-induced compaction proceeds. In contrast,
the total length of force chains remains unchanged. From the correlations of
those parameters, we find two relations: (i) a positive correlation between the
isotropy of grain configurations and the disordering of force-chain
orientations, and (ii) a negative correlation between the increasing of
interparticle forces and the disordering of force-chain orientations. These
relations are universally held regardless of the mode of particle motions
with/without convection
Relativistic Einstein-Podolsky-Rosen correlation and Bell's inequality
We formulate the Einstein-Podolsky-Rosen (EPR) gedankenexperiment within the
framework of relativistic quantum theory to analyze a situation in which
measurements are performed by moving observers. We point out that under certain
conditions the perfect anti-correlation of an EPR pair of spins in the same
direction is deteriorated in the moving observers' frame due to the Wigner
rotation, and show that the degree of the violation of Bell's inequality prima
facie decreases with increasing the velocity of the observers if the directions
of the measurement are fixed. However, this does not imply a breakdown of
non-local correlation since the perfect anti-correlation is maintained in
appropriately chosen different directions. We must take account of this
relativistic effect in utilizing in moving frames the EPR correlation and the
violation of Bell's inequality for quantum communication.Comment: 33 pages, 6 figure
Nonunitary quantum circuit
A quantum circuit is generalized to a nonunitary one whose constituents are
nonunitary gates operated by quantum measurement. It is shown that a specific
type of one-qubit nonunitary gates, the controlled-NOT gate, as well as all
one-qubit unitary gates constitute a universal set of gates for the nonunitary
quantum circuit, without the necessity of introducing ancilla qubits. A
reversing measurement scheme is used to improve the probability of successful
nonunitary gate operation. A quantum NAND gate and Abrams-Lloyd's nonlinear
gate are analyzed as examples. Our nonunitary circuit can be used to reduce the
qubit overhead needed to ensure fault-tolerant quantum computation.Comment: 19 pages, 6 figures; added a referenc
BCS-BEC crossover in a relativistic superfluid and its significance to quark matter
The character change of a superfluid state due to the variation of the
attractive force is investigated in the relativistic framework with a massive
fermion. Two crossovers are found. One is a crossover from the usual BCS state
to the Bose-Einstein condensation (BEC) of bound fermion pairs. The other is
from the BEC to the relativistic Bose-Einstein condensation (RBEC) of nearly
massless bound pairs where antiparticles as well as particles dominate the
thermodynamics. Possible realization of the BEC and RBEC states in the quark
matter is also pointed out.Comment: 5 pages, 1 figure, revtex4; (v2) text has been clarified, references
updated; (v3) final version to appear in Phys. Rev.
Orbital-controlled magnetic transition between gapful and gapless phases in the Haldane system with t2g-orbital degeneracy
In order to clarify a key role of orbital degree of freedom in the spin S=1
Haldane system, we investigate ground-state properties of the t2g-orbital
degenerate Hubbard model on the linear chain by using numerical techniques.
Increasing the Hund's rule coupling in multi-orbital systems, in general, there
occurs a transition from an antiferromagnetic to a ferromagnetic phase. We find
that the antiferromagnetic phase is described as the Haldane system with spin
gap, while in the ferromagnetic phase, there exists the gapless excitation with
respect to orbital degree of freedom. Possible relevance of the present results
to actual systems is also discussed.Comment: 4 pages, 3 figures, to appear in Phys. Rev.
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