336 research outputs found
Continuous variable quantum cryptography
We propose a quantum cryptographic scheme in which small phase and amplitude
modulations of CW light beams carry the key information. The presence of EPR
type correlations provides the quantum protection.Comment: 8 pages, 3 figure
Reversal of age-related learning deficiency by the vertebrate PACAP and IGF-1 in a novel invertebrate model of aging: the pond snail (Lymnaea Stagnalis)
With the increase of life span, nonpathological age-related memory decline is affecting an increasing number of people. However, there is evidence that age-associated memory impairment only suspends, rather than irreversibly extinguishes, the intrinsic capacity of the aging nervous system for plasticity (1). Here, using a molluscan model system, we show that the age-related decline in memory performance can be reversed by administration of the pituitary adenylate cyclase activating polypeptide (PACAP). Our earlier findings showed that a homolog of the vertebrate PACAP38 and its receptors exist in the pond snail (Lymnaea stagnalis) brain (2), and it is both necessary and instructive for memory formation after reward conditioning in young animals (3). Here we show that exogenous PACAP38 boosts memory formation in aged Lymnaea, where endogenous PACAP38 levels are low in the brain. Treatment with insulin-like growth factor-1, which in vertebrates was shown to transactivate PACAP type I (PAC1) receptors (4) also boosts memory formation in aged pond snails. Due to the evolutionarily conserved nature of these polypeptides and their established role in memory and synaptic plasticity, there is a very high probability that they could also act as “memory rejuvenating” agents in humans
The response of the magnetosphere to the passage of a coronal mass ejection on March 20–21 1990
First observations of SPEAR-induced artificial backscatter from CUTLASS and the EISCAT Svalbard radars
Results are presented from the first two active experimental campaigns undertaken by the new SPEAR (Space Plasma Exploration by Active Radar) high-power system that has recently become operational on Spitzbergen, in the Svalbard archipelago. SPEAR's high-power beam was used to excite artificial enhancements in the backscatter detected by the ESR (EISCAT Svalbard Radar) parallel to the geomagnetic field, as well as coherent backscatter detected by both of the CUTLASS (Co-operative UK Twin Located Auroral Sounding System) coherent radars, in directions orthogonal to the geomagnetic field. The ESR detected both enhanced ion-lines as well as enhanced plasma-lines, that were sustained for the whole period when SPEAR was transmitting ordinary mode radio waves, at frequencies below the maximum F-region plasma frequency. On a number of occasions, coherent backscatter was also observed in one or in both of the CUTLASS radars, in beams that intersected the heated volume. Although the levels of enhanced backscatter varied considerably in time, it appeared that ion-line, plasma-line and coherent backscatter were all excited simultaneously, in contrast to what has typically been reported at Tromsø, during EISCAT heater operations. A description of the technical and operational aspects of the new SPEAR system is also included
Mimicking a Squeezed Bath Interaction: Quantum Reservoir Engineering with Atoms
The interaction of an atomic two-level system and a squeezed vacuum leads to
interesting novel effects in atomic dynamics, including line narrowing in
resonance fluorescence and absorption spectra, and a suppressed (enhanced)
decay of the in-phase and out-of phase component of the atomic polarization. On
the experimental side these predictions have so far eluded observation,
essentially due to the difficulty of embedding atoms in a 4 pi squeezed vacuum.
In this paper we show how to ``engineer'' a squeezed-bath-type interaction for
an effective two-level system. In the simplest example, our two-level atom is
represented by the two ground levels of an atom with angular momentum J=1/2 ->
J=1/2 transition (a four level system) which is driven by (weak) laser fields
and coupled to the vacuum reservoir of radiation modes. Interference between
the spontaneous emission channels in optical pumping leads to a squeezed bath
type coupling, and thus to symmetry breaking of decay on the Bloch sphere. With
this system it should be possible to observe the effects predicted in the
context of squeezed bath - atom interactions. The laser parameters allow one to
choose properties of the squeezed bath interaction, such as the (effective)
photon number expectation number N and the squeezing phase phi. We present
results of a detailed analytical and numerical study.Comment: 24 pages, 8 figure
First observations of SPEAR-induced artificial backscatter from CUTLASS and the EISCAT Svalbard radars
Interferometric Tests of Teleportation
We investigate a direct test of teleportation efficacy based on a
Mach-Zehnder interferometer. The analysis is performed for continuous variable
teleportation of both discrete and continuous observables
Creating a Stir: The role of Word of Mouth in Reputation Management in the Context of Festivals
This qualitative case study examines the role of word of mouth (WOM) in reputation management in the context of networked festival productions. Particularly, it explores the ways in which WOM marketing (WOMM) is employed in festival marketing and brand-building. The paper links reputation and WOM to the concept of cultural branding with the aim of providing a framework for analysing how a festival's reputation shapes the creation of a culturally meaningful message. The empirical analysis is based on a multiple-case study involving three Finnish festivals hosted in the city of Pori: the Porispere Festival, the International Pori Jazz Festival and the International Lain�uojattomat Theatre Festival. The cases represent festivals of different sizes and varying organisational structure, content and life cycle. The findings indicate that the meaning and use of WOMM vary depending on key constitutive differences that affect the nature of the festivals? reputation and brand-building processes. Although the importance of external and internal stakeholders in these processes is evident, it seems that when the power of networks is recognised as crucial for festivals, WOM has a leveraging role in reputation management and brand-building. In these processes, the value of the festival leader's persona becomes crucial
Theory of Pseudomodes in Quantum Optical Processes
This paper deals with non-Markovian behaviour in atomic systems coupled to a
structured reservoir of quantum EM field modes, with particular relevance to
atoms interacting with the field in high Q cavities or photonic band gap
materials. In cases such as the former, we show that the pseudo mode theory for
single quantum reservoir excitations can be obtained by applying the Fano
diagonalisation method to a system in which the atomic transitions are coupled
to a discrete set of (cavity) quasimodes, which in turn are coupled to a
continuum set of (external) quasimodes with slowly varying coupling constants
and continuum mode density. Each pseudomode can be identified with a discrete
quasimode, which gives structure to the actual reservoir of true modes via the
expressions for the equivalent atom-true mode coupling constants. The quasimode
theory enables cases of multiple excitation of the reservoir to now be treated
via Markovian master equations for the atom-discrete quasimode system.
Applications of the theory to one, two and many discrete quasimodes are made.
For a simple photonic band gap model, where the reservoir structure is
associated with the true mode density rather than the coupling constants, the
single quantum excitation case appears to be equivalent to a case with two
discrete quasimodes
- …