26,685 research outputs found
Barrier-controlled carrier transport in microcrystalline semiconducting materials: Description within a unified model
A recently developed model that unifies the ballistic and diffusive transport
mechanisms is applied in a theoretical study of carrier transport across
potential barriers at grain boundaries in microcrystalline semiconducting
materials. In the unified model, the conductance depends on the detailed
structure of the band edge profile and in a nonlinear way on the carrier mean
free path. Equilibrium band edge profiles are calculated within the trapping
model for samples made up of a linear chain of identical grains. Quantum
corrections allowing for tunneling are included in the calculation of electron
mobilities. The dependence of the mobilities on carrier mean free path, grain
length, number of grains, and temperature is examined, and appreciable
departures from the results of the thermionic-field-emission model are found.
Specifically, the unified model is applied in an analysis of Hall mobility data
for n-type microcrystalline Si thin films in the range of thermally activated
transport. Owing mainly to the effect of tunneling, potential barrier heights
derived from the data are substantially larger than the activation energies of
the Hall mobilities. The specific features of the unified model, however,
cannot be resolved within the rather large uncertainties of the analysis.Comment: REVTex, 19 pages, 9 figures; to appear in J. Appl. Phy
More efficient Bell inequalities for Werner states
In this paper we study the nonlocal properties of two-qubit Werner states
parameterized by the visibility parameter 0<p<1. New family of Bell
inequalities are constructed which prove the two-qubit Werner states to be
nonlocal for the parameter range 0.7056<p<1. This is slightly wider than the
range 0.7071<p<1, corresponding to the violation of the
Clauser-Horne-Shimony-Holt (CHSH) inequality. This answers a question posed by
Gisin in the positive, i.e., there exist Bell inequalities which are more
efficient than the CHSH inequality in the sense that they are violated by a
wider range of two-qubit Werner states.Comment: 7 pages, 1 figur
Universal joint-measurement uncertainty relation for error bars
We formulate and prove a new, universally valid uncertainty relation for the necessary error bar widths in any approximate joint measurement of position and momentum
On separability of quantum states and the violation of Bell-type inequalities
In contrast to the wide-spread opinion that any separable quantum state
satisfies every classical probabilistic constraint, we present a simple example
where a separable quantum state does not satisfy the original Bell inequality
although the latter inequality, in its perfect correlation form, is valid for
all joint classical measurements. In a very general setting, we discuss
inequalities for joint experiments upon a bipartite quantum system in a
separable state. We derive quantum analogues of the original Bell inequality
and specify the conditions sufficient for a separable state to satisfy the
original Bell inequality. We introduce the extended CHSH inequality and prove
that, for any separable quantum state, this inequality holds for a variety of
linear combinations.Comment: 13 pages, extended versio
The statistical strength of experiments to reject local realism with photon pairs and inefficient detectors
Because of the fundamental importance of Bell's theorem, a loophole-free
demonstration of a violation of local realism (LR) is highly desirable. Here,
we study violations of LR involving photon pairs. We quantify the experimental
evidence against LR by using measures of statistical strength related to the
Kullback-Leibler (KL) divergence, as suggested by van Dam et al. [W. van Dam,
R. Gill and P. Grunwald, IEEE Trans. Inf. Theory. 51, 2812 (2005)].
Specifically, we analyze a test of LR with entangled states created from two
independent polarized photons passing through a polarizing beam splitter. We
numerically study the detection efficiency required to achieve a specified
statistical strength for the rejection of LR depending on whether photon
counters or detectors are used. Based on our results, we find that a test of LR
free of the detection loophole requires photon counters with efficiencies of at
least 89.71%, or photon detectors with efficiencies of at least 91.11%. For
comparison, we also perform this analysis with ideal unbalanced Bell states,
which are known to allow rejection of LR with detector efficiencies above 2/3.Comment: 18 pages, 3 figures, minor changes (add more references, replace the
old plots, etc.)
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