59,192 research outputs found
Non-vanishing Berry Phase in Chiral Insulators
The binary compounds FeSi, RuSi, and OsSi are chiral insulators crystallizing
in the space group P2_13 which is cubic. By means of ab initio calculations we
find for these compounds a non-vanishing electronic Berry phase, the sign of
which depends on the handedness of the crystal. There is thus the possibility
that the Berry phase signals the existence of a macroscopic electric
polarization due to the electrons. We show that this is indeed so if a small
external magnetic field is applied in the [111]-direction. The electric
polarization is oscillatory in the magnetic field and possesses a signature
that distinguishes the handedness of the crystal. Our findings add to the
discussion of topological classifications of insulators and are significant for
spintronics applications, and in particular, for a deeper understanding of
skyrmions in insulators
Measure of multipartite entanglement with computable lower bounds
In this paper, we present a measure of multipartite entanglement
(-nonseparable), -ME concurrence that
unambiguously detects all -nonseparable states in arbitrary dimensions,
where the special case, 2-ME concurrence , is a
measure of genuine multipartite entanglement. The new measure -ME
concurrence satisfies important characteristics of an entanglement measure
including entanglement monotone, vanishing on -separable states, convexity,
subadditivity and strictly greater than zero for all -nonseparable states.
Two powerful lower bounds on this measure are given. These lower bounds are
experimentally implementable without quantum state tomography and are easily
computable as no optimization or eigenvalue evaluation is needed. We illustrate
detailed examples in which the given bounds perform better than other known
detection criteria.Comment: 12 pages, 3 figure
- …