643 research outputs found
A limit on nonlocality in any world in which communication complexity is not trivial
Bell proved that quantum entanglement enables two space-like separated
parties to exhibit classically impossible correlations. Even though these
correlations are stronger than anything classically achievable, they cannot be
harnessed to make instantaneous (faster than light) communication possible.
Yet, Popescu and Rohrlich have shown that even stronger correlations can be
defined, under which instantaneous communication remains impossible. This
raises the question: Why are the correlations achievable by quantum mechanics
not maximal among those that preserve causality? We give a partial answer to
this question by showing that slightly stronger correlations would result in a
world in which communication complexity becomes trivial.Comment: 13 pages, no figure
Pressure shift of the superconducting T_c of LiFeAs
The effect of hydrostatic pressure on the superconductivity in LiFeAs is
investigated up to 1.8 GPa. The superconducting transition temperature, T_c,
decreases linearly with pressure at a rate of 1.5 K/GPa. The negative pressure
coefficient of T_c and the high ambient pressure T_c indicate that LiFeAs is
the high-pressure analogue of the isoelectronic SrFe_2As_2 and BaFe_2As_2.Comment: 3 pages, 2 figure
Optimality of private quantum channels
We addressed the question of optimality of private quantum channels. We have
shown that the Shannon entropy of the classical key necessary to securely
transfer the quantum information is lower bounded by the entropy exchange of
the private quantum channel and von Neumann entropy of the ciphertext
state . Based on these bounds we have shown that decomposition
of private quantum channels into orthogonal unitaries (if exists) is optimizing
the entropy. For non-ancillary single qubit PQC we have derived the optimal
entropy for arbitrary set of plaintexts. In particular, we have shown that
except when the (closure of the) set of plaintexts contains all states, one bit
key is sufficient. We characterized and analyzed all the possible single qubit
private quantum channels for arbitrary set of plaintexts. For the set of
plaintexts consisting of all qubit states we have characterized all possible
approximate private quantum channels and we have derived the relation between
the security parameter and the corresponding minimal entropy.Comment: no commen
Superconductivity at 38 K in Iron-Based Compound with Platinum-Arsenide Layers Ca10(Pt4As8)(Fe2-xPtxAs2)5
We report superconductivity in novel iron-based compounds
Ca10(PtnAs8)(Fe2-xPtxAs2)5 with n = 3 and 4. Both compounds crystallize in
triclinic structures (space group P-1), in which Fe2As2 layers alternate with
PtnAs8 spacer layers. Superconductivity with a transition temperature of 38 K
is observed in the n = 4 compound with a Pt content of x ~ 0.36 in the Fe2As2
layers. The compound with n = 3 exhibits superconductivity at 13 K.Comment: OPEN SELECT article, 11 pages, 5 figures, 2 table
Crossover from commensurate to incommensurate antiferromagnetism in stoichiometric NaFeAs revealed by single-crystal 23Na,75As-NMR experiments
We report results of 23Na and 75As nuclear magnetic resonance (NMR)
experiments on a self-flux grown high-quality single crystal of stoichiometric
NaFeAs. The NMR spectra revealed a tetragonal to twinned-orthorhombic
structural phase transition at T_O = 57 K and an antiferromagnetic (AF)
transition at T_AF = 45 K. The divergent behavior of nuclear relaxation rate
near T_AF shows significant anisotropy, indicating that the critical slowing
down of stripe-type AF fluctuations are strongly anisotropic in spin space. The
NMR spectra at low enough temperatures consist of sharp peaks showing a
commensurate stripe AF order with a small moment \sim 0.3 muB. However, the
spectra just below T_AF exhibits highly asymmetric broadening pointing to an
incommensurate modulation. The commensurate-incommensurate crossover in NaFeAs
shows a certain similarity to the behavior of SrFe2As2 under high pressure.Comment: 5 pages, 5 figures, revised version to appear in J. Phys. Soc. Jp
First-Principles Study for the Anisotropy of Iron-based Superconductors toward Power and Device Applications
Performing the first-principles calculations, we investigate the anisotropy
in the superconducting state of iron-based superconductors to gain an insight
into their potential applications. The anisotropy ratio of the
c-axis penetration depth to the ab-plane one is relatively small in BaFe2As2
and LiFeAs, i.e., , indicating that the transport
applications are promising in these superconductors. On the other hand, in
those having perovskite type blocking layers such as Sr2ScFePO3 we find a very
large value, , comparable to that in strongly
anisotropic high-Tc cuprate Bi2Sr2CaCu2O{8-\delta}. Thus, the intrinsic
Josephson junction stacks are expected to be formed along the c-axis, and novel
Josephson effects due to the multi-gap nature are also suggested in these
superconductors.Comment: 5 pages, 4 figure
Structural study on hole-doped superconductors Pr1-xSrxFeAsO
The structural details in Pr1-xSrxFeAsO (1111) superconducting system are
analyzed using data obtained from synchrotron X-ray diffraction and the
structural parameters are carefully studied as the system is moving from
non-superconducting to hole-doped superconducting with the Sr concentration.
Superconductivity emerges when the Sr doping amount reaches 0.221. The linear
increase of the lattice constants proves that Sr is successfully introduced
into the system and its concentration can accurately be determined by the
electron density analyses. The evolution of structural parameters with Sr
concentration in Pr1-xSrxFeAsO and their comparison to other similar structural
parameters of the related Fe-based superconductors suggest that the interlayer
space between the conducting As-Fe-As layer and the insulating Pr-O-Pr layer is
important for improving Tc in the hole-doped (1111) superconductors, which
seems to be different from electron-doped systems.Comment: 17 pages, 7 figures, 1 tabl
Nutritional factors and gender influence age-related DNA methylation in the human rectal mucosa
Aberrant methylation of CpG islands (CGI) occurs in many genes expressed in colonic epithelial cells, and may contribute to the dysregulation of signalling pathways associated with carcinogenesis. This cross-sectional study assessed the relative importance of age, nutritional exposures and other environmental factors in the development of CGI methylation. Rectal biopsies were obtained from 185 individuals (84 male, 101 female) shown to be free of colorectal disease, and for whom measurements of age, body size, nutritional status and blood cell counts were available. We used quantitative DNA methylation analysis combined with multivariate modelling to investigate the relationships between nutritional, anthropometric and metabolic factors and the CGI methylation of 11 genes, together with LINE-1 as an index of global DNA methylation. Age was a consistent predictor of CGI methylation for 9/11 genes but significant positive associations with folate status and negative associations with vitamin D and selenium status were also identified for several genes. There was evidence for positive associations with blood monocyte levels and anthropometric factors for some genes. In general, CGI methylation was higher in males than in females and differential effects of age and other factors on methylation in males and females were identified. In conclusion, levels of age-related CGI methylation in the healthy human rectal mucosa are influenced by gender, the availability of folate, vitamin D and selenium, and perhaps by factors related to systemic inflammatio
Heavy anion solvation of polarity fluctuations in Pnictides
Once again the condensed matter world has been surprised by the discovery of
yet another class of high temperature superconductors. The discovery of
iron-pnictide (FeAs) and chalcogenide (FeSe) based superconductors with a
of up to 55 K is again evidence of how complex the many body problem really is,
or in another view how resourceful nature is. The first reactions would of
course be that these new materials must in some way be related to the
copper-oxide based superconductors for which a large number of theories exist
although a general consensus regarding the correct theory has not yet been
reached. Here we point out that the basic physical paradigm of the new iron
based superconductors is entirely different from the cuprates. Their
fundamental properties, structural and electronic, are dominated by the
exceptionally large pnictide polarizabilities
Determination of the Upper Critical Field of a Single Crystal LiFeAs: The Magnetic Torque Study up to 35 Tesla
We report on the upper critical field B_c2 of a superconducting LiFeAs single
crystal with T_c~16 K, determined from magnetic torque measurements in
dc-magnetic fields up to 35 T and at temperatures down to 0.3 K. B_c2 at 0.3 K
is obtained to be 26.4 T and 15.5 T for the applied field B_a||ab and B_a||c,
respectively. The anisotropy parameter = is ~ 3 at
T_c and decreases to 1.7 as , showing rather isotropic
superconductivity. While B_c2 is orbitally-limited for B_a||c, the
spin-paramagnetic effect is evident in the temperature dependence of B_c2 for
B_a||abComment: 4 pages, 4 figures, revised version to be published in J. Phys. Soc.
Jpn. as a letter articl
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