408 research outputs found
HI scaling relations of galaxies in the environment of HI-rich and control galaxies observed by the Bluedisk project
Our work is based on the "Bluedisk" project, a program to map the neutral gas
in a sample of 25 HI-rich spirals and a similar number of control galaxies with
the Westerbork Synthesis Radio Telescope (WSRT). In this paper we focus on the
HI properties of the galaxies in the environment of our targeted galaxies. In
total, we extract 65 galaxies from the WSRT cubes with stellar masses between
and . Most of these galaxies are located on
the same HI mass-size relation and "HI-plane" as normal spiral galaxies. We
find that companions around HI-rich galaxies tend to be HI-rich as well and to
have larger R90,HI/R50,HI. This suggests a scenario of "HI conformity", similar
to the colour conformity found by Weinmann et al. (2006): galaxies tend to
adopt the HI properties of their neighbours. We visually inspect the outliers
from the HI mass-size relation and galaxies which are offset from the HI plane
and find that they show morphological and kinematical signatures of recent
interactions with their environment. We speculate that these outliers have been
disturbed by tidal or ram-pressure stripping processes, or in a few cases, by
accretion events.Comment: 16 pages, 12 figures; accepted for publication in MNRA
Distinguishability of States and von Neumann Entropy
Consider an ensemble of pure quantum states |\psi_j>, j=1,...,n taken with
prior probabilities p_j respectively. We show that it is possible to increase
all of the pairwise overlaps || i.e. make each constituent pair
of the states more parallel (while keeping the prior probabilities the same),
in such a way that the von Neumann entropy S is increased, and dually, make all
pairs more orthogonal while decreasing S. We show that this phenomenon cannot
occur for ensembles in two dimensions but that it is a feature of almost all
ensembles of three states in three dimensions. It is known that the von Neumann
entropy characterises the classical and quantum information capacities of the
ensemble and we argue that information capacity in turn, is a manifestation of
the distinguishability of the signal states. Hence our result shows that the
notion of distinguishability within an ensemble is a global property that
cannot be reduced to considering distinguishability of each constituent pair of
states.Comment: 18 pages, Latex, 2 figure
Basic Logic and Quantum Entanglement
As it is well known, quantum entanglement is one of the most important
features of quantum computing, as it leads to massive quantum parallelism,
hence to exponential computational speed-up. In a sense, quantum entanglement
is considered as an implicit property of quantum computation itself. But...can
it be made explicit? In other words, is it possible to find the connective
"entanglement" in a logical sequent calculus for the machine language? And
also, is it possible to "teach" the quantum computer to "mimic" the EPR
"paradox"? The answer is in the affirmative, if the logical sequent calculus is
that of the weakest possible logic, namely Basic logic. A weak logic has few
structural rules. But in logic, a weak structure leaves more room for
connectives (for example the connective "entanglement"). Furthermore, the
absence in Basic logic of the two structural rules of contraction and weakening
corresponds to the validity of the no-cloning and no-erase theorems,
respectively, in quantum computing.Comment: 10 pages, 1 figure,LaTeX. Shorter version for proceedings
requirements. Contributed paper at DICE2006, Piombino, Ital
On quantum coding for ensembles of mixed states
We consider the problem of optimal asymptotically faithful compression for
ensembles of mixed quantum states. Although the optimal rate is unknown, we
prove upper and lower bounds and describe a series of illustrative examples of
compression of mixed states. We also discuss a classical analogue of the
problem.Comment: 23 pages, LaTe
Off-diagonal geometric phase for mixed states
We extend the off-diagonal geometric phase [Phys. Rev. Lett. {\bf 85}, 3067
(2000)] to mixed quantal states. The nodal structure of this phase in the qubit
(two-level) case is compared with that of the diagonal mixed state geometric
phase [Phys. Rev. Lett. {\bf 85}, 2845 (2000)]. Extension to higher dimensional
Hilbert spaces is delineated. A physical scenario for the off-diagonal mixed
state geometric phase in polarization-entangled two-photon interferometry is
proposed.Comment: small corrections; journal reference adde
Quantum entanglement and classical communication through a depolarising channel
We analyse the role of entanglement for transmission of classical information
through a memoryless depolarising channel. Using the isotropic character of
this channel we prove analytically that the mutual information cannot be
increased by encoding classical bits into entangled states of two qubits.Comment: 6 pages, 2 figures; contribution to special issue of JMO on the
physics of quantum information; 2nd version: slight modifications and
improved presentatio
Connections of geometric measure of entanglement of pure symmetric states to quantum state estimation
We study the geometric measure of entanglement (GM) of pure symmetric states
related to rank-one positive-operator-valued measures (POVMs) and establish a
general connection with quantum state estimation theory, especially the maximum
likelihood principle. Based on this connection, we provide a method for
computing the GM of these states and demonstrate its additivity property under
certain conditions. In particular, we prove the additivity of the GM of pure
symmetric multiqubit states whose Majorana points under Majorana representation
are distributed within a half sphere, including all pure symmetric three-qubit
states. We then introduce a family of symmetric states that are generated from
mutually unbiased bases (MUBs), and derive an analytical formula for their GM.
These states include Dicke states as special cases, which have already been
realized in experiments. We also derive the GM of symmetric states generated
from symmetric informationally complete POVMs (SIC~POVMs) and use it to
characterize all inequivalent SIC~POVMs in three-dimensional Hilbert space that
are covariant with respect to the Heisenberg--Weyl group. Finally, we describe
an experimental scheme for creating the symmetric multiqubit states studied in
this article and a possible scheme for measuring the permanent of the related
Gram matrix.Comment: 11 pages, 1 figure, published versio
Visible compression of commuting mixed states
We analyze the problem of quantum data compression of commuting density
operators in the visible case. We show that the lower bound for the compression
factor given by the Levitin--Holevo function is reached by providing an
explicit protocol.Comment: 7 pages, no figure
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