The Origin of Antibunching in Resonance Fluorescence

Epitaxial quantum dots have emerged as one of the best single-photon sources, not only for applications in photonic quantum technologies but also for testing fundamental properties of quantum optics. One intriguing observation in this area is the scattering of photons with subnatural linewidth from a two-level system under resonant continuous wave excitation. In particular, an open question is whether these subnatural linewidth photons exhibit simultaneously antibunching as an evidence of single-photon emission. Here, we demonstrate that this simultaneous observation of subnatural linewidth and antibunching is not possible with simple resonant excitation. First, we independently confirm single-photon character and subnatural linewidth by demonstrating antibunching in a Hanbury Brown and Twiss type setup and using high-resolution spectroscopy, respectively. However, when filtering the coherently scattered photons with filter bandwidths on the order of the homogeneous linewidth of the excited state of the two-level system, the antibunching dip vanishes in the correlation measurement. Our experimental work is consistent with recent theoretical findings, that explain antibunching from photon-interferences between the coherent scattering and a weak incoherent signal in a skewed squeezed state.Comment: 8 pages, 4 figure

Origin of antibunching in resonance fluorescence

Resonance fluorescence has played a major role in quantum optics with predictions and later experimental confirmation of nonclassical features of its emitted light such as antibunching or squeezing. In the Rayleigh regime where most of the light originates from the scattering of photons with subnatural linewidth, antibunching would appear to coexist with sharp spectral lines. Here, we demonstrate that this simultaneous observation of subnatural linewidth and antibunching is not possible with simple resonant excitation. Using an epitaxial quantum dot for the two-level system, we independently confirm the single-photon character and subnatural linewidth by demonstrating antibunching in a Hanbury Brown and Twiss type setup and using high-resolution spectroscopy, respectively. However, when filtering the coherently scattered photons with filter bandwidths on the order of the homogeneous linewidth of the excited state of the two-level system, the antibunching dip vanishes in the correlation measurement. Our observation is explained by antibunching originating from photon-interferences between the coherent scattering and a weak incoherent signal in a skewed squeezed state. This prefigures schemes to achieve simultaneous subnatural linewidth and antibunched emissio

The decision to vaccinate or not during the H1N1 pandemic: selecting the lesser of two evils?

BACKGROUND: With the release of the H1N1 vaccine, there was much controversy surrounding its use despite strong encouragements to be vaccinated in the media. Though studies have examined factors influencing people's decision to be vaccinated, few have focused on how general beliefs about the world or where an individual gathers information might influence that decision. METHODOLOGY/PRINCIPAL FINDINGS: A cross-sectional web-based survey (N = 817) was conducted during the H1N1 outbreak after the vaccine was available. Variables examined included sociodemographic information, health related behaviours, specific beliefs concerning the H1N1 virus and its vaccine, as well as general beliefs, such as fear of contamination, intolerance of uncertainty, emotional states, coping behaviour, and the source of information concerning the virus. Three converging statistical methods were used to examine the associations - analysis of variance, logistic regression, and recursive partition modelling. The most consistent and strongest association was that negative beliefs about the H1N1 vaccine (e.g. fear of its side effects) was related to the decision not to be vaccinated, whereas beliefs about the dangers of the H1N1 virus was related to the decision to be vaccinated. Most notably, having very strong negative beliefs about the vaccine was a more powerful predictor than even strong beliefs about the dangers of the H1N1 virus. Furthermore, obtaining information from the Internet, as compared to more traditional sources of information (e.g., TV, newspapers) was related to the decision not to be vaccinated. CONCLUSIONS/SIGNIFICANCE: These results are consistent with the Health Belief Model. Importantly they suggest that during future pandemics public health officials should not only discuss the dangers of the pandemic but also (i) take additional steps to reassure the public about the safety of vaccines and (ii) monitor the information disseminated over the Internet rather than strictly relying on the more traditional mass media

Most influential information source for the decision to be vaccinated.

<p><i>Note:</i> Cells represent the percentage of participants in each group who endorsed the item as being most influential in their decision.</p

Odds ratio for vaccination intention (Yes or No/Undecided) (<i>N</i> = 816).

<p><i>Note</i>: Odds ratios (OR) that have a 95% confidence interval that includes the value 1.0 are not significant at the .05 level.</p>a<p>Reference category for ethnicity is Caucasian.</p>b<p>Reference category for High Risk Group is no.</p>c<p>Reference category for Health Professional is no.</p>d<p>Reference category for Preferred Information Source is Discussions with Friends and Family.</p>*<p><i>p</i><.10, * <i>p</i><.05; <i>** p</i><.01.</p

Classification and regression tree (CART) model depicting variables discriminating those who were (Yes) and were not vaccinated or were undecided (No).

<p><i>Note</i>: The square box with double lines represents the starting node, all other square boxes represent terminal nodes. Circular boxes represent nodes containing branches. The title contained within circular boxes indicates the measure used to divide participants into the next node with the dividing values indicated along the arrows. <i>Neg Vac Beliefs</i>  =  Negative Vaccination Beliefs.</p

Score on the Pandemic Behaviour Questionnaire and Vaccination Questionnaire by vaccination intention groups.

<p><i>Note.</i> Means with differing superscripts (e.g., ^{x, y, z}) indicate a significant difference at the .05 level or more.</p>a<p>df  = 2, 813.</p>**<p><i>p</i><.001.</p

Sociodemographics of participants by vaccination intention.

*<p>At risk groups were defined as individuals indicating that they are currently pregnant, have a chronic medical condition, are immune suppressed, or have children at home under the age of 5.</p>a<p>χ² = 36.52, <i>p</i><.001.</p>b<p>χ² = 30.22, <i>p</i><.001.</p>c<p>χ² = 16.70, <i>p</i><.001.</p