8,525 research outputs found
Splittings of groups and intersection numbers
We prove algebraic analogues of the facts that a curve on a surface with
self-intersection number zero is homotopic to a cover of a simple curve, and
that two simple curves on a surface with intersection number zero can be
isotoped to be disjoint.Comment: 40 pages. Published copy, also available at
http://www.maths.warwick.ac.uk/gt/GTVol4/paper6.abs.htm
Local and global statistical distances are equivalent on pure states
The statistical distance between pure quantum states is obtained by finding a
measurement that is optimal in a sense defined by Wootters. As such, one may
expect that the statistical distance will turn out to be different if the set
of possible measurements is restricted in some way. It nonetheless turns out
that if the restriction is to local operations and classical communication
(LOCC) on any multipartite system, then the statistical distance is the same as
it is without restriction, being equal to the angle between the states in
Hilbert space.Comment: 5 pages, comments welcom
Holidaying with the family pet: No dogs allowed!
This paper assesses the extent to which dog owners located in Brisbane, Australia, wish to holiday with their pets, and whether there is a gap between this desire and reality. The paper also examines the extent to which this demand is being catered for by the tourism accommodation sector. The need for this study reflects the increasingly significant role dogs are playing in the lives of humans, and the scale
of the dog-owning population. The results suggest that, although there is a strong desire among dog owners to take holidays with their pets, the actualisation of this
desire is comparatively low. A significant obstacle to the realisation of this desire appears to be a dearth of pet-friendly accommodation. This has implications for the
ability of the tourism industry to benefit from this potentially lucrative market, that is, the dog-owning population
Atemporal diagrams for quantum circuits
A system of diagrams is introduced that allows the representation of various
elements of a quantum circuit, including measurements, in a form which makes no
reference to time (hence ``atemporal''). It can be used to relate quantum
dynamical properties to those of entangled states (map-state duality), and
suggests useful analogies, such as the inverse of an entangled ket. Diagrams
clarify the role of channel kets, transition operators, dynamical operators
(matrices), and Kraus rank for noisy quantum channels. Positive (semidefinite)
operators are represented by diagrams with a symmetry that aids in
understanding their connection with completely positive maps. The diagrams are
used to analyze standard teleportation and dense coding, and for a careful
study of unambiguous (conclusive) teleportation. A simple diagrammatic argument
shows that a Kraus rank of 3 is impossible for a one-qubit channel modeled
using a one-qubit environment in a mixed state.Comment: Minor changes in references. Latex 32 pages, 13 figures in text using
PSTrick
Women's Work and European Fertility Patterns
http://deepblue.lib.umich.edu/bitstream/2027.42/50872/1/95.pd
Rethinking Visiting Friends and Relatives Mobilities
The increasing number of people leading more mobile lives, with spatially dispersed families, raises questions over how they maintain their family life and friendships, and how this is shaped and shapes different forms of migration, and different patterns of Visiting Friends and Relatives (VFR). This paper develops an explanatory framework for conceptualizing and analyzing VFR mobilities, seeking to draw together threads from migration, mobilities and tourism studies. In unpacking the notion of VFR, this paper understands VFR mobilities as being constituted of diverse practices, and discusses five of the most important of these: social relationships, the provision of care, affirmations of identities and roots, maintenance of territorial rights, and leisure tourism. While these five types of practices are considered sequentially in this paper, they are in practice often blurred and overlapping. The interweaving of these practices changes over time, as does the meaning and content of individual practices, reflecting changes in the duration of migration, life cycle stage, individual goals and values, and the broader sets of relationships with and social obligations to different kin and friends
Spectral structure near the 11.3 micron emission feature
If the 11.3 micron emission feature seen in the spectra of many planetary nebulae, H II regions, and reflection nebulae is attributable to polycyclic aromatic hydrocarbons (PAHs), then additional features should be present between 11.3 and 13.0 microns. Moderate resolution spectra of NGC 7027, HD 44179, BD+30 deg 3639, and IRAS 21282+5050 are presented which show evidence for new emission features centered near 12.0 and 12.7 microns. These are consistent with an origin from PAHs and can be used to constrain the molecular structure of the family of PAHs responsible for the infrared features. There is an indication that coronene-like PAHs contribute far more to the emission from NGC 7027 than to the emission from HD 44179. The observed asymmetric profile of the 11.3 micron band in all the spectra is consistent with the slight anharmonicity expected in the C-H out-of-plane bending mode in PAHs. A series of repeating features between 10 and 11 microns in the spectrum of HD 44179 suggests a simple hydride larger than 2 atoms is present in the gas phase in this object
Deterministic and Unambiguous Dense Coding
Optimal dense coding using a partially-entangled pure state of Schmidt rank
and a noiseless quantum channel of dimension is studied both in
the deterministic case where at most messages can be transmitted with
perfect fidelity, and in the unambiguous case where when the protocol succeeds
(probability ) Bob knows for sure that Alice sent message , and when
it fails (probability ) he knows it has failed. Alice is allowed any
single-shot (one use) encoding procedure, and Bob any single-shot measurement.
For a bound is obtained for in terms of the largest
Schmidt coefficient of the entangled state, and is compared with published
results by Mozes et al. For it is shown that is strictly
less than unless is an integer multiple of , in which case
uniform (maximal) entanglement is not needed to achieve the optimal protocol.
The unambiguous case is studied for , assuming for a
set of messages, and a bound is obtained for the average
\lgl1/\tau\rgl. A bound on the average \lgl\tau\rgl requires an additional
assumption of encoding by isometries (unitaries when ) that are
orthogonal for different messages. Both bounds are saturated when is a
constant independent of , by a protocol based on one-shot entanglement
concentration. For it is shown that (at least) messages can
be sent unambiguously. Whether unitary (isometric) encoding suffices for
optimal protocols remains a major unanswered question, both for our work and
for previous studies of dense coding using partially-entangled states,
including noisy (mixed) states.Comment: Short new section VII added. Latex 23 pages, 1 PSTricks figure in
tex
Local cloning of entangled states
We investigate the conditions under which a set \SC of pure bipartite
quantum states on a system can be locally cloned deterministically
by separable operations, when at least one of the states is full Schmidt rank.
We allow for the possibility of cloning using a resource state that is less
than maximally entangled. Our results include that: (i) all states in \SC
must be full Schmidt rank and equally entangled under the -concurrence
measure, and (ii) the set \SC can be extended to a larger clonable set
generated by a finite group of order , the number of states in the
larger set. It is then shown that any local cloning apparatus is capable of
cloning a number of states that divides exactly. We provide a complete
solution for two central problems in local cloning, giving necessary and
sufficient conditions for (i) when a set of maximally entangled states can be
locally cloned, valid for all ; and (ii) local cloning of entangled qubit
states with non-vanishing entanglement. In both of these cases, a maximally
entangled resource is necessary and sufficient, and the states must be related
to each other by local unitary "shift" operations. These shifts are determined
by the group structure, so need not be simple cyclic permutations. Assuming
this shifted form and partially entangled states, then in D=3 we show that a
maximally entangled resource is again necessary and sufficient, while for
higher dimensional systems, we find that the resource state must be strictly
more entangled than the states in \SC. All of our necessary conditions for
separable operations are also necessary conditions for LOCC, since the latter
is a proper subset of the former. In fact, all our results hold for LOCC, as
our sufficient conditions are demonstrated for LOCC, directly.Comment: REVTEX 15 pages, 1 figure, minor modifications. Same as the published
version. Any comments are welcome
- âŠ