6,373 research outputs found
The entanglement beam splitter: a quantum-dot spin in a double-sided optical microcavity
We propose an entanglement beam splitter (EBS) using a quantum-dot spin in a
double-sided optical microcavity. In contrast to the conventional optical beam
splitter, the EBS can directly split a photon-spin product state into two
constituent entangled states via transmission and reflection with high fidelity
and high efficiency (up to 100 percent). This device is based on giant optical
circular birefringence induced by a single spin as a result of cavity quantum
electrodynamics and the spin selection rule of trion transition (Pauli
blocking). The EBS is robust and it is immune to the fine structure splitting
in a realistic quantum dot. This quantum device can be used for
deterministically creating photon-spin, photon-photon and spin-spin
entanglement as well as a single-shot quantum non-demolition measurement of a
single spin. Therefore, the EBS can find wide applications in quantum
information science and technology.Comment: 7 pages, 5 figure
On being oneself: a comparison of Heidegger and Buber on personal identity
The question is posed, what does it mean to be oneself?
It is argued that to look for an answer in the psycho-physical
characteristics of the individual himself does not take account of
man's restless refusal to be content with what he is. The starting
point of the inquiry is that an understanding of what makes man himself
must take account of the 'beyond' in terms of which he seeks to define
himself. It is this preliminary assumption which explains how Heidegger
and Buber come to be considered together, for both philosophers share
the view that man is an ec-static being, one who 'stands out' from
himself in some way. However, it is precisely when Heidegger and
Buber are juxtaposed that the problem of the thesis is set, for their
views seem mutually exclusive. In Heidegger's understanding a. man is
only himself when he steps forth towards his own possibility of non¬
existence. In contrast for Buber it is the relation of love which
enables a person to be himself. The purpose of the comparison is to
attempt to face the reality of death for each person with its effect
on identity, and also the reality of the love of another person freeing
one to be oneself.The argument is presented that man's relation with man as
Buber presents it requires a radical reconstruction of Heidegger's
analysis of existence. It is suggested that through the reality of love
which resists the world 'as it is', including the power of death, the
boundaries of existence need to be redefined. If love is accepted as
an ontological phenomenon, then its appearance does not seem to be
explicable within Heidegger's ontology of Being-towards-death. It is
noted, on the other hand, that if it is possible to build an alternative
ontology on love, the final possibility of death cannot be sidestepped.
It is here that Heidegger can be used to strengthen Buber's notion of
relation, for Buber seems to ignore the finitude of man, and the threat
it poses to the 'I-Thou' relation as an ontological category.In the final section of the thesis, it is argued that the
phenomenon of love cannot have its roots in this dying world. It is
suggested that an explanation of the reality of love and its power to
create personal Being requires an eschatological perspective. Only
from such a perspective, with its refusal to accept death as a condition
of man being himself, can an alternative ontology to Heidegger's be
found.The conclusion reached is that the concept of God is
implicit in the view of selfhood developed in the thesis. In accordance
with that conclusion, in the final chapter some theological implications
of a relational view of the self are outlined. In particular, the
question is asked whether Persons-in-Trinity can be viewed as the
ultimate resource for personhood. Pinally, requirements for a
Christological anthropology consistent with a relational selfhood, are
considered
Giant optical Faraday rotation induced by a single electron spin in a quantum dot: Applications to entangling remote spins via a single photon
We propose a quantum non-demolition method - giant Faraday rotation - to
detect a single electron spin in a quantum dot inside a microcavity where
negatively-charged exciton strongly couples to the cavity mode. Left- and
right-circularly polarized light reflected from the cavity feels different
phase shifts due to cavity quantum electrodynamics and the optical spin
selection rule. This yields giant and tunable Faraday rotation which can be
easily detected experimentally. Based on this spin-detection technique, a
scalable scheme to create an arbitrary amount of entanglement between two or
more remote spins via a single photon is proposed.Comment: 5 pages, 3 figure
Efficient optical quantum information processing
Quantum information offers the promise of being able to perform certain
communication and computation tasks that cannot be done with conventional
information technology (IT). Optical Quantum Information Processing (QIP) holds
particular appeal, since it offers the prospect of communicating and computing
with the same type of qubit. Linear optical techniques have been shown to be
scalable, but the corresponding quantum computing circuits need many auxiliary
resources. Here we present an alternative approach to optical QIP, based on the
use of weak cross-Kerr nonlinearities and homodyne measurements. We show how
this approach provides the fundamental building blocks for highly efficient
non-absorbing single photon number resolving detectors, two qubit parity
detectors, Bell state measurements and finally near deterministic control-not
(CNOT) gates. These are essential QIP devicesComment: Accepted to the Journal of optics B special issue on optical quantum
computation; References update
Single photon quantum non-demolition in the presence of inhomogeneous broadening
Electromagnetically induced transparency (EIT) has been often proposed for
generating nonlinear optical effects at the single photon level; in particular,
as a means to effect a quantum non-demolition measurement of a single photon
field. Previous treatments have usually considered homogeneously broadened
samples, but realisations in any medium will have to contend with inhomogeneous
broadening. Here we reappraise an earlier scheme [Munro \textit{et al.} Phys.
Rev. A \textbf{71}, 033819 (2005)] with respect to inhomogeneities and show an
alternative mode of operation that is preferred in an inhomogeneous
environment. We further show the implications of these results on a potential
implementation in diamond containing nitrogen-vacancy colour centres. Our
modelling shows that single mode waveguide structures of length in single-crystal diamond containing a dilute ensemble of NV
of only 200 centres are sufficient for quantum non-demolition measurements
using EIT-based weak nonlinear interactions.Comment: 21 pages, 9 figures (some in colour) at low resolution for arXiv
purpose
Layer by layer generation of cluster states
Cluster states can be used to perform measurement-based quantum computation.
The cluster state is a useful resource, because once it has been generated only
local operations and measurements are needed to perform universal quantum
computation. In this paper, we explore techniques for quickly and
deterministically building a cluster state. In particular we consider
generating cluster states on a qubus quantum computer, a computational
architecture which uses a continuous variable ancilla to generate interactions
between qubits. We explore several techniques for building the cluster, with
the number of operations required depending on whether we allow the ability to
destroy previously created controlled-phase links between qubits. In the case
where we can not destroy these links, we show how to create an n x m cluster
using just 3nm -2n -3m/2 + 3 operations. This gives more than a factor of 2
saving over a naive method. Further savings can be obtained if we include the
ability to destroy links, in which case we only need (8nm-4n-4m-8)/3
operations. Unfortunately the latter scheme is more complicated so choosing the
correct order to interact the qubits is considerably more difficult. A half way
scheme, that keeps a modular generation but saves additional operations over
never destroying links requires only 3nm-2n-2m+4 operations. The first scheme
and the last scheme are the most practical for building a cluster state because
they split up the generation into the repetition of simple sections.Comment: 16 pages, 11 figure
The efficiencies of generating cluster states with weak non-linearities
We propose a scalable approach to building cluster states of matter qubits
using coherent states of light. Recent work on the subject relies on the use of
single photonic qubits in the measurement process. These schemes can be made
robust to detector loss, spontaneous emission and cavity mismatching but as a
consequence the overhead costs grow rapidly, in particular when considering
single photon loss. In contrast, our approach uses continuous variables and
highly efficient homodyne measurements. We present a two-qubit scheme, with a
simple bucket measurement system yielding an entangling operation with success
probability 1/2. Then we extend this to a three-qubit interaction, increasing
this probability to 3/4. We discuss the important issues of the overhead cost
and the time scaling. This leads to a "no-measurement" approach to building
cluster states, making use of geometric phases in phase space.Comment: 21 pages, to appear in special issue of New J. Phys. on
"Measurement-Based Quantum Information Processing
Decoy Effects in Choice Experiments and Contingent Valuation: Asymmetric Dominance
While a dominated choice involves a situation in which one option clearly dominates another on all relevant dimensions, an asymmetrically dominated choice typically arises where at least two options do not dominate each other and one (but not both) of those options does dominate a third option. We demonstrate that the introduction of such an asymmetrically dominated option can have a significant impact upon choices between non-dominated options within the same choice set for non-market goods. Furthermore, we show that this effect can then translate into significant impacts upon subsequent valuations for those non-dominated options.Preprinthttp://www.grips.ac.jp/list/jp/facultyinfo/munro_alistair
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