30,103 research outputs found
Entanglement Induced Fluctuations of Cold Bosons
We show that due to entanglement, quantum fluctuations may differ
significantly from statistical fluctuations. We calculate quantum fluctuations
of the particle number and of the energy in a sub-volume of a system of bosons
in a pure state, and briefly discuss the possibility of measuring them. We find
that energy fluctuations have a non-extensive nature.Comment: Replaced with published version. Added calculations, explanations and
clarifications, results unchange
Probing polymer chain constraint and synergistic effects in nylon 6-clay nanocomposites and nylon 6-silica flake sub-micro composites with nanomechanics
In this study, we report that a synergistic effect exists in the surface mechanical properties of nylon 6–clay nanocomposites (NC) that can be shown by nanomechanical testing. The hardness, elastic modulus, and nanoindentation creep behavior of nylon 6 and its nanocomposites with different filler loading produced by melt compounding were contrasted to those of model nylon 6 sub-microcomposites (SMC) reinforced by sub-micro-thick silica flakes in which constraint cannot occur due to the difference in filler geometry. Polymer chain constraint was assessed by the analysis of nanoindentation creep data. Time-dependent creep decreased with increasing the filler loading in the NC consistent with the clay platelets exerting a constraint effect on the polymer chains which increases with filler loading. In contrast, there was no evidence of any reduced time-dependent creep for the SMC samples, consistent with a lack of constraint expected due to much lower aspect ratio of the silica flake
Scanning SQUID Susceptometry of a paramagnetic superconductor
Scanning SQUID susceptometry images the local magnetization and
susceptibility of a sample. By accurately modeling the SQUID signal we can
determine the physical properties such as the penetration depth and
permeability of superconducting samples. We calculate the scanning SQUID
susceptometry signal for a superconducting slab of arbitrary thickness with
isotropic London penetration depth, on a non-superconducting substrate, where
both slab and substrate can have a paramagnetic response that is linear in the
applied field. We derive analytical approximations to our general expression in
a number of limits. Using our results, we fit experimental susceptibility data
as a function of the sample-sensor spacing for three samples: 1) delta-doped
SrTiO3, which has a predominantly diamagnetic response, 2) a thin film of
LaNiO3, which has a predominantly paramagnetic response, and 3) a
two-dimensional electron layer (2-DEL) at a SrTiO3/AlAlO3 interface, which
exhibits both types of response. These formulas will allow the determination of
the concentrations of paramagnetic spins and superconducting carriers from fits
to scanning SQUID susceptibility measurements.Comment: 11 pages, 13 figure
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.)
State-dependent rotations of spins by weak measurements
IIt is shown that a weak measurement of a quantum system produces a new state
of the quantum system which depends on the prior state, as well as the
(uncontrollable) measured position of the pointer variable of the weak
measurement apparatus. The result imposes a constraint on hidden-variable
theories which assign a different state to a quantum system than standard
quantum mechanics. The constraint means that a crypto-nonlocal hidden-variable
theory can be ruled out in a more direct way than previously.Comment: 10 pages, 2 figures. Substantially revised to concentrate on weak
measurement transformation of states and application to crypto-nonlocal
hidden-variable theor
Irreducible MultiQutrit Correlations in Greenberger-Horne-Zeilinger Type States
Following the idea of the continuity approach in [D. L. Zhou, Phys. Rev.
Lett. 101, 180505 (2008)], we obtain the degrees of irreducible multi-party
correlations in two families of -qutrit Greenberger-Horne-Zeilinger type
states. For the pure states in one of the families, the irreducible 2-party,
-party and -party () correlations are nonzero, which is
different from the -qubit case. We also derive the correlation distributions
in the -qutrit maximal slice state, which can be uniquely determined by its
-qutrit reduced density matrices among pure states. It is proved that
there is no irreducible -qutrit correlation in the maximal slice state. This
enlightens us to give a discussion about how to characterize the pure states
with irreducible -party correlation in arbitrarily high-dimensional systems
by the way of the continuity approach.Comment: 5p, no fi
Unified criteria for multipartite quantum nonlocality
Wiseman and co-workers (Phys. Rev. Lett. 98, 140402, 2007) proposed a
distinction between the nonlocality classes of Bell's nonlocality, steering and
entanglement based on whether or not an overseer trusts each party in a
bipartite scenario where they are asked to demonstrate entanglement. Here we
extend that concept to the multipartite case and derive inequalities that
progressively test for those classes of nonlocality, with different thresholds
for each level. This framework includes the three classes of nonlocality above
in special cases and introduces a family of others.Comment: V2: corrected image display; V3: substantial changes including new
proofs, arguments, and result
The Identity Correspondence Problem and its Applications
In this paper we study several closely related fundamental problems for words
and matrices. First, we introduce the Identity Correspondence Problem (ICP):
whether a finite set of pairs of words (over a group alphabet) can generate an
identity pair by a sequence of concatenations. We prove that ICP is undecidable
by a reduction of Post's Correspondence Problem via several new encoding
techniques.
In the second part of the paper we use ICP to answer a long standing open
problem concerning matrix semigroups: "Is it decidable for a finitely generated
semigroup S of square integral matrices whether or not the identity matrix
belongs to S?". We show that the problem is undecidable starting from dimension
four even when the number of matrices in the generator is 48. From this fact,
we can immediately derive that the fundamental problem of whether a finite set
of matrices generates a group is also undecidable. We also answer several
question for matrices over different number fields. Apart from the application
to matrix problems, we believe that the Identity Correspondence Problem will
also be useful in identifying new areas of undecidable problems in abstract
algebra, computational questions in logic and combinatorics on words.Comment: We have made some proofs clearer and fixed an important typo from the
published journal version of this article, see footnote 3 on page 1
Light to Mass Variations with Environment
Large and well defined variations exist between the distribution of mass and
the light of stars on extragalactic scales. Mass concentrations in the range
10^12 - 10^13 M_sun manifest the most light per unit mass. Group halos in this
range are typically the hosts of spiral and irregular galaxies with ongoing
star formation. On average M/L_B ~ 90 M_sun/L_sun in these groups . More
massive halos have less light per unit mass. Within a given mass range, halos
that are dynamically old as measured by crossing times and galaxy morphologies
have distinctly less light per unit mass. At the other end of the mass
spectrum, below 10^12 M_sun, there is a cutoff in the manifestation of light.
Group halos in the range 10^11 - 10^12 M_sun can host dwarf galaxies but with
such low luminosities that M/L_B values can range from several hundred to
several thousand. It is suspected that there must be completely dark halos at
lower masses. Given the form of the halo mass function, it is the low relative
luminosities of the high mass halos that has the greatest cosmological
implications. Of order half the clustered mass may reside in halos with greater
than 10^14 M_sun. By contrast, only 5-10% of clustered mass would lie in
entities with less than 10^12 M_sun.Comment: 15 pages, 9 figures, 2 tables, Accepted Astrophysical Journal 619,
000, 2005 (Jan 1
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