6,973 research outputs found
Quantum phase estimation using path-symmetric entangled states
We study the sensitivity of phase estimation using a generic class of
path-symmetric entangled states
, where an arbitrary state
occupies one of two modes in quantum superposition. This
class of states includes the previously considered states, i.e. states
and entangled coherent states, as special cases. With its generalization, we
identify the practical limit of phase estimation under energy constraint that
is characterized by the photon statistics of the component state
. We first show that quantum Cramer-Rao bound (QCRB) can be
lowered with super-Poissonianity of the state . By introducing
a component state of the form
, we particularly show
that an arbitrarily small QCRB can be achieved even with a finite energy in an
ideal situation. For practical measurement schemes, we consider a parity
measurement and a full photon-counting method to obtain phase-sensitivity.
Without photon loss, the latter scheme employing any path-symmetric states
achieves the QCRB over the
entire range of unknown phase shift whereas the former does
so in a certain confined range of . We find that the case of
provides the most
robust resource against loss among the considered entangled states over the
whole range of input energy. Finally we also propose experimental schemes to
generate these path-symmetric entangled states.Comment: 10 pages, 5 figures, published versio
Increasing and decreasing entanglement characteristics for continuous variables by a local photon subtraction
We investigate how the entanglement characteristics of a non-Gaussian
entangled state are increased or decreased by a local photon subtraction
operation. The non-Gaussian entangled state is generated by injecting a
single-mode non-Gaussian state and a vacuum state into a 50:50 beam splitter.
We consider a photon-added coherent state and an odd coherent state as a
single-mode non-Gaussian state. In the regime of small amplitude, we show that
the performance of quantum teleportation and the second-order
Einstein-Podolsky- Rosen-type correlation can both be enhanced, whereas the
degree of entanglement decreases, for the output state when a local photon
subtraction operation is applied to the non-Gaussian entangled state. The
counterintuitive effect is more prominent in the limit of nearly zero
amplitude.Comment: Published version, 7 pages, 3 figure
City farming and sustainable urban development :a case study of Seoul, South Korea
PhD ThesisThe aims of the thesis are to find out the causal mechanism of city farming and
to examine the hypothesis that city farming conforms to the conditions of
sustainable urban development. As far as methodology is concerned, the thesis
employs a realist approach. In the realist methodology, to understand what is as
significant as to know why. Therefore, the thesis pays much attention to the
conceptualisation of city farming and sustainable urban development.
Vacant land in Seoul, the precondition of city farming, occurred basically
through the natural process of urban expansion, but most importantly due to
the growth-oriented land development policies. City farming is at the moment
an opportunistic and illegal use of vacant land under the negligence of planning
control. Led by a leading agent, the city farmers on each case site have
colonised vacant land through the reality and practice learning. However, city
farmers' egoistic action has an unintended consequence of making vacant land
an unofficial open space. The thesis also identifies that city farming on the case
sites conforms to the elements of sustainable urban development. The elements
developed in the thesis are future, nature, participation, equity, and selfreliance.
The thesis suggests three criteria for each element with which the
hypothesis is examined.
The thesis concludes that the modern planning system in South Korea has failed
to take into consideration the socio-economic and environmental aspects of city
farming. It, therefore, suggests that future planning system promote activities
or projects which comply with the principles of sustainable urban development.
Although the modern planning system in Seoul has failed to cope with the
rapid land use change shown in the case studies, the thesis proposes that the
planner's role has become more important than ever before in this age of
environmental concerns
The Octonions
The octonions are the largest of the four normed division algebras. While
somewhat neglected due to their nonassociativity, they stand at the crossroads
of many interesting fields of mathematics. Here we describe them and their
relation to Clifford algebras and spinors, Bott periodicity, projective and
Lorentzian geometry, Jordan algebras, and the exceptional Lie groups. We also
touch upon their applications in quantum logic, special relativity and
supersymmetry.Comment: 56 pages LaTeX, 11 Postscript Figures, some small correction
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