208 research outputs found
Cat States and Single Runs for the Damped Harmonic Oscillator
We discuss the fate of initial states of the cat type for the damped harmonic
oscillator, mostly employing a linear version of the stochastic Schr\"odinger
equation. We also comment on how such cat states might be prepared and on the
relation of single realizations of the noise to single runs of experiments.Comment: 18, Revte
An entangled two photon source using biexciton emission of an asymmetric quantum dot in a cavity
A semiconductor based scheme has been proposed for generating entangled
photon pairs from the radiative decay of an electrically-pumped biexciton in a
quantum dot. Symmetric dots produce polarisation entanglement, but
experimentally-realised asymmetric dots produce photons entangled in both
polarisation and frequency. In this work, we investigate the possibility of
erasing the `which-path' information contained in the frequencies of the
photons produced by asymmetric quantum dots to recover polarisation-entangled
photons. We consider a biexciton with non-degenerate intermediate excitonic
states in a leaky optical cavity with pairs of degenerate cavity modes close to
the non-degenerate exciton transition frequencies. An open quantum system
approach is used to compute the polarisation entanglement of the two-photon
state after it escapes from the cavity, measured by the visibility of
two-photon interference fringes. We explicitly relate the two-photon visibility
to the degree of Bell-inequality violation, deriving a threshold at which
Bell-inequality violations will be observed. Our results show that an ideal
cavity will produce maximally polarisation-entangled photon pairs, and even a
non-ideal cavity will produce partially entangled photon pairs capable of
violating a Bell-inequality.Comment: 16 pages, 10 figures, submitted to PR
The resource theory of quantum reference frames: manipulations and monotones
Every restriction on quantum operations defines a resource theory,
determining how quantum states that cannot be prepared under the restriction
may be manipulated and used to circumvent the restriction. A superselection
rule is a restriction that arises through the lack of a classical reference
frame and the states that circumvent it (the resource) are quantum reference
frames. We consider the resource theories that arise from three types of
superselection rule, associated respectively with lacking: (i) a phase
reference, (ii) a frame for chirality, and (iii) a frame for spatial
orientation. Focussing on pure unipartite quantum states (and in some cases
restricting our attention even further to subsets of these), we explore
single-copy and asymptotic manipulations. In particular, we identify the
necessary and sufficient conditions for a deterministic transformation between
two resource states to be possible and, when these conditions are not met, the
maximum probability with which the transformation can be achieved. We also
determine when a particular transformation can be achieved reversibly in the
limit of arbitrarily many copies and find the maximum rate of conversion. A
comparison of the three resource theories demonstrates that the extent to which
resources can be interconverted decreases as the strength of the restriction
increases. Along the way, we introduce several measures of frameness and prove
that these are monotonically nonincreasing under various classes of operations
that are permitted by the superselection rule.Comment: 37 pages, 4 figures, Published Versio
Non-destructive, dynamic detectors for Bose-Einstein condensates
We propose and analyze a series of non-destructive, dynamic detectors for
Bose-Einstein condensates based on photo-detectors operating at the shot noise
limit. These detectors are compatible with real time feedback to the
condensate. The signal to noise ratio of different detection schemes are
compared subject to the constraint of minimal heating due to photon absorption
and spontaneous emission. This constraint leads to different optimal operating
points for interference-based schemes. We find the somewhat counter-intuitive
result that without the presence of a cavity, interferometry causes as much
destruction as absorption for optically thin clouds. For optically thick
clouds, cavity-free interferometry is superior to absorption, but it still
cannot be made arbitrarily non-destructive . We propose a cavity-based
measurement of atomic density which can in principle be made arbitrarily
non-destructive for a given signal to noise ratio
How equitable is bed net ownership and utilisation in Tanzania? A practical application of the principles of horizontal and vertical equity
BACKGROUND: Studies show that the burden of malaria remains huge particularly in low-income settings. Although effective malaria control measures such as insecticide-treated nets (ITNs) have been promoted, relatively little is known about their equity dimension. Understanding variations in their use in low-income settings is important for scaling up malaria control programmes particularly ITNs. The objective of this paper is to measure the extent and causes of inequalities in the ownership and utilisation of bed nets across socioeconomic groups (SEGs) and age groups in Tanga District, north-eastern Tanzania. METHODS: A questionnaire was administered to heads of 1,603 households from rural and urban areas. Households were categorized into SEGs using both an asset-based wealth index and education level of the household head. Concentration indices and regression-based measures of inequality were computed to analyse both vertical and horizontal inequalities in ownership and utilisation of bed nets. Focus Group Discussions (FGDs) were used to explore community perspectives on the causes of inequalities. RESULTS: Use of ITNs remained appallingly low compared to the RBM target of 80% coverage. Inequalities in ownership of ITNs and all nets combined were significantly pro-rich and were much more pronounced in rural areas. FGDs revealed that lack of money was the key factor for not using ITNs followed by negative perceptions about the effect of insecticides on the health of users. Household SES, living within the urban areas and being under-five were positively associated with bed net ownership and/or utilisation. CONCLUSION: The results highlight the need for mass distribution of ITN; a community-wide programme to treat all untreated nets and to promote the use of Long-Lasting Insecticidal nets (LLINs) or longer-lasting treatment of nets. The rural population and under-fives should be targeted through highly subsidized schemes and mass distribution of free nets. Public campaigns are also needed to encourage people to use treated nets and mitigate negative perceptions about insecticides
Radioimmunotherapy Improves Survival of Rats with Microscopic Liver Metastases of Colorectal Origin
BACKGROUND: Half of the patients with colorectal cancer develop liver metastases during the course of their disease. The aim of the present study was to assess the efficacy of radioimmunotherapy (RIT) with a radiolabeled monoclonal antibody (mAb) to treat experimental colorectal liver metastases. METHODS: Male Wag/Rij rats underwent a minilaparotomy with intraportal injection of 1 x 10(6) CC531 tumor cells. The biodistribution of (111)In-labeled MG1, 1 day after intravenous administration, was determined in vivo and compared with that of an isotype-matched control antibody (UPC-10). The maximal tolerated dose (MTD) of (177)Lu-labeled MG1 was determined and the therapeutic efficacy of (177)Lu-MG1 at MTD was compared with that of (177)Lu-UPC-10 and saline only. RIT was administered either at the day of tumor inoculation or 14 days after tumor inoculation. Primary endpoint was survival. RESULTS: (111)In-MG1 preferentially accumulated in CC531 liver tumors (9.2 +/- 3.7%ID/g), whereas (111)In-UPC-10 did not (0.8 +/- 0.1%ID/g). The MTD of (177)Lu-MG1 was 400 MBq/kg body weight. Both the administration of (177)Lu-MG1 and (177)Lu-UPC-10 had no side-effects except a transient decrease in body weight. The survival curves of the group that received (177)Lu-UPC-10 and the group that received saline only did not differ (P = 0.407). Administration of (177)Lu-MG1 RIT immediately after surgery improved survival significantly compared with administration of (177)Lu-UPC-10 (P = 0.009) whereas delayed treatment did not (P = 0.940). CONCLUSION: This study provides proof of principle that RIT can be an effective treatment modality for microscopic liver metastases, whereas RIT is not effective in larger tumors
A First Search for coincident Gravitational Waves and High Energy Neutrinos using LIGO, Virgo and ANTARES data from 2007
We present the results of the first search for gravitational wave bursts
associated with high energy neutrinos. Together, these messengers could reveal
new, hidden sources that are not observed by conventional photon astronomy,
particularly at high energy. Our search uses neutrinos detected by the
underwater neutrino telescope ANTARES in its 5 line configuration during the
period January - September 2007, which coincided with the fifth and first
science runs of LIGO and Virgo, respectively. The LIGO-Virgo data were analysed
for candidate gravitational-wave signals coincident in time and direction with
the neutrino events. No significant coincident events were observed. We place
limits on the density of joint high energy neutrino - gravitational wave
emission events in the local universe, and compare them with densities of
merger and core-collapse events.Comment: 19 pages, 8 figures, science summary page at
http://www.ligo.org/science/Publication-S5LV_ANTARES/index.php. Public access
area to figures, tables at
https://dcc.ligo.org/cgi-bin/DocDB/ShowDocument?docid=p120000
A cellular trafficking signal in the SIV envelope protein cytoplasmic domain is strongly selected for in pathogenic infection
The HIV/SIV envelope glycoprotein (Env) cytoplasmic domain contains a highly conserved Tyr-based trafficking signal that mediates both clathrin-dependent endocytosis and polarized sorting. Despite extensive analysis, the role of these functions in viral infection and pathogenesis is unclear. An SIV molecular clone (SIVmac239) in which this signal is inactivated by deletion of Gly-720 and Tyr-721 (SIVmac239ÎGY), replicates acutely to high levels in pigtail macaques (PTM) but is rapidly controlled. However, we previously reported that rhesus macaques and PTM can progress to AIDS following SIVmac239ÎGY infection in association with novel amino acid changes in the Env cytoplasmic domain. These included an R722G flanking the ÎGY deletion and a nine nucleotide deletion encoding amino acids 734â736 (ÎQTH) that overlaps the rev and tat open reading frames. We show that molecular clones containing these mutations reconstitute signals for both endocytosis and polarized sorting. In one PTM, a novel genotype was selected that generated a new signal for polarized sorting but not endocytosis. This genotype, together with the ÎGY mutation, was conserved in association with high viral loads for several months when introduced into naĂŻve PTMs. For the first time, our findings reveal strong selection pressure for Env endocytosis and particularly for polarized sorting during pathogenic SIV infection in vivo
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