1,817 research outputs found
Genuine Multiparty Quantum Entanglement Suppresses Multiport Classical Information Transmission
We establish a universal complementarity relation between the capacity of
classical information transmission by employing a multiparty quantum state as a
multiport quantum channel, and the genuine multipartite entanglement of the
quantum state. The classical information transfer is from a sender to several
receivers by using the quantum dense coding protocol with the multiparty
quantum state shared between the sender and the receivers. The relation holds
for arbitrary pure or mixed quantum states of an arbitrary number of parties in
arbitrary dimensions.Comment: 5 (+ epsilon) pages, 2 figures, Revtex4-1; v2: Theorem 3 extended to
all states, other results unchange
Quantum Information Processing with Ferroelectrically Coupled Quantum Dots
I describe a proposal to construct a quantum information processor using
ferroelectrically coupled Ge/Si quantum dots. The spin of single electrons form
the fundamental qubits. Small (<10 nm diameter) Ge quantum dots are optically
excited to create spin polarized electrons in Si. The static polarization of an
epitaxial ferroelectric thin film confines electrons laterally in the
semiconductor; spin interactions between nearest neighbor electrons are
mediated by the nonlinear process of optical rectification. Single qubit
operations are achieved through "g-factor engineering" in the Ge/Si structures;
spin-spin interactions occur through Heisenberg exchange, controlled by
ferroelectric gates. A method for reading out the final state, while required
for quantum computing, is not described; electronic approaches involving single
electron transistors may prove fruitful in satisfying this requirement.Comment: 10 pages, 3 figure
Towards a Precision Cosmology from Starburst Galaxies at z>2
This work investigates the use of a well-known empirical correlation between
the velocity dispersion, metallicity, and luminosity in H beta of nearby HII
galaxies to measure the distances to HII-like starburst galaxies at high
redshifts. This correlation is applied to a sample of 15 starburst galaxies
with redshifts between z=2.17 and z=3.39 to constrain Omega_m, using data
available from the literature. A best-fit value of Omega_m = 0.21 +0.30 -0.12
in a Lambda-dominated universe and of Omega_m = 0.11 +0.37 -0.19 in an open
universe is obtained. A detailed analysis of systematic errors, their causes,
and their effects on the values derived for the distance moduli and Omega_m is
carried out. A discussion of how future work will improve constraints on
Omega_m by reducing the errors is also presented.Comment: 7 pages, 3 figures, accepted for publication in MNRA
Instability of reconstruction of the low CMB multipoles
We discuss the problem of the bias of the Internal Linear Combination (ILC)
CMB map and show that it is closely related to the coefficient of
cross-correlation K(l) of the true CMB and the foreground for each multipole l.
We present analysis of the cross-correlation for the WMAP ILC quadrupole and
octupole from the first (ILC(I)) and the third (ILC(III)) year data releases
and show that these correlations are about -0.52-0.6. Analysing 10^4 Monte
Carlo simulations of the random Gaussian CMB signals, we show that the
distribution function for the corresponding coefficient of the
cross-correlation has a polynomial shape P(K,l)\propto(1-K^2)^(l-1). We show
that the most probable value of the cross-correlation coefficient of the ILC
and foreground quadrupole has two extrema at K ~= +/-0.58$. Thus, the ILC(III)
quadrupole represents the most probable value of the coefficient K. We analyze
the problem of debiasing of the ILC CMB and pointed out that reconstruction of
the bias seems to be very problematic due to statistical uncertainties. In
addition, instability of the debiasing illuminates itself for the quadrupole
and octupole components through the flip-effect, when the even (l+m) modes can
be reconstructed with significant error. This error manifests itself as
opposite, in respect to the true sign of even low multipole modes, and leads to
significant changes of the coefficient of cross-correlation with the
foreground. We show that the CMB realizations, whose the sign of quadrupole
(2,0) component is negative (and the same, as for all the foregrounds), the
corresponding probability to get the positive sign after implementation of the
ILC method is about 40%.Comment: 11 pages, 5 figure
Random Oracles in a Quantum World
The interest in post-quantum cryptography - classical systems that remain
secure in the presence of a quantum adversary - has generated elegant proposals
for new cryptosystems. Some of these systems are set in the random oracle model
and are proven secure relative to adversaries that have classical access to the
random oracle. We argue that to prove post-quantum security one needs to prove
security in the quantum-accessible random oracle model where the adversary can
query the random oracle with quantum states.
We begin by separating the classical and quantum-accessible random oracle
models by presenting a scheme that is secure when the adversary is given
classical access to the random oracle, but is insecure when the adversary can
make quantum oracle queries. We then set out to develop generic conditions
under which a classical random oracle proof implies security in the
quantum-accessible random oracle model. We introduce the concept of a
history-free reduction which is a category of classical random oracle
reductions that basically determine oracle answers independently of the history
of previous queries, and we prove that such reductions imply security in the
quantum model. We then show that certain post-quantum proposals, including ones
based on lattices, can be proven secure using history-free reductions and are
therefore post-quantum secure. We conclude with a rich set of open problems in
this area.Comment: 38 pages, v2: many substantial changes and extensions, merged with a
related paper by Boneh and Zhandr
On the Origins of the High-Latitude H-alpha Background
The diffuse high-latitude H-alpha background is widely believed to be
predominantly the result of in-situ recombination of ionized hydrogen in the
warm interstellar medium of the Galaxy. Instead, we show that both a
substantial fraction of the diffuse high-latitude H-alpha intensity in regions
dominated by Galactic cirrus dust and much of the variance in the high-latitude
H-alpha background are the result of scattering by interstellar dust of H-alpha
photons originating elsewhere in the Galaxy. We provide an empirical relation,
which relates the expected scattered H-alpha intensity to the IRAS 100um
diffuse background intensity, applicable to about 81% of the entire sky. The
assumption commonly made in reductions of CMB observations, namely that the
observed all-sky map of diffuse H-alpha light is a suitable template for
Galactic free-free foreground emission, is found to be in need of
reexamination.Comment: 26 pages, 5 figures, Accepted for publication in Ap
On religion and cultural policy: notes on the Roman Catholic Church
This paper argues that religious institutions have largely been neglected within the study of cultural policy. This is attributed to the inherently secular tendency of most modern social sciences. Despite the predominance of the ‘secularisation paradigm’, the paper notes that religion continues to promote powerful attachments and denunciations. Arguments between the ‘new atheists’, in particular, Richard Dawkins, and their opponents are discussed, as is Habermas’s conciliatory encounter with Joseph Ratzinger (later Pope Benedict XVI). The paper then moves to a consideration of the Roman Catholic Church as an agent of cultural policy, whose overriding aim is the promotion of ‘Christian consciousness’. Discussion focuses on the contested meanings of this, with reference to (1) the deliberations of Vatican II and (2) the exercise of theological and cultural authority by the Pope and the Congregation for the Doctrine of the Faith (CDF). It is argued that these doctrinal disputes intersect with secular notions of social and cultural policy and warrant attention outside the specialist realm of theological discourse
Optimal Controlled teleportation via several kinds of three-qubit states
The probability of successfully controlled teleportating an unknown qubit
using a general three-particle state is investigated. We give the analytic
expressions of maximal probabilities of successfully controlled teleportating
an unknown qubit via several kinds of tripartite states including a tripartite
GHZ state and a tripartite W-state.Comment: 15 page
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