Nonclassical photon pair production in a voltage-biased Josephson junction

We investigate electromagnetic radiation emitted by a small voltage-biased Josephson junction connected to a superconducting transmission line. At frequencies below the well known emission peak at the Josephson frequency (2eV/h), extra radiation is triggered by quantum fluctuations in the electromagnetic environment. For weak tunneling couplings and typical ohmic transmission lines, the corresponding photon flux spectrum is symmetric around half the Josephson frequency, indicating that the photons are predominately created in pairs. By establishing an input-output formalism for the microwave field in the transmission line, we give further evidence for this nonclassical photon pair production, demonstrating that it violates the classical Cauchy-Schwarz inequality for two-mode flux cross correlations. In connection to recent experiments, we also consider a stepped transmission line, where resonances increase the signal-to-noise ratio.Comment: 5 pages, 2 figures. This version accepted in Physical Review Letter

Input-output description of microwave radiation in the dynamical Coulomb blockade

We study microwave radiation emitted by a small voltage-biased Josephson junction connected to a superconducting transmission line. An input-output formalism for the radiation field is established, using a perturbation expansion in the junction's critical current. Using output field operators solved up to the second order, we estimate the spectral density and the second-order coherence of the emitted field. For typical transmission line impedances and at frequencies below the main emission peak at the Josephson frequency, radiation occurs predominantly due to two-photon emission. This emission is characterized by a high degree of photon bunching if detected symmetrically around half of the Josephson frequency. Strong phase fluctuations in the transmission line make related nonclassical phase-dependent amplitude correlations short lived, and there is no steady-state two-mode squeezing. However, the radiation is shown to violate the classical Cauchy-Schwarz inequality of intensity cross-correlations, demonstrating the nonclassicality of the photon pair production in this region.Comment: 29 pages, 4 figure

On the non-linearity of the willingness to commute

Established analysis of labour market commuting are based on random choice models and gravity type models. In these models generalised transport costs are formulated as exponential or loglinear distance-dependent functions. This paper presents empirical observations that imply that time-distances influence the commuting behaviour in a non-linear way, such that the time sensitivity is much lower for very short and long distances, whereas intermediate distance display a high time sensitivity. This is explained in a model which is parametrised and estimated. The results are important for understanding and predicting commuter behaviour. It also helps to delineate space, as in classical traditions, into local, intra-regional, and extra-regional space.

Constructing cities, deconstructing scaling laws

Cities can be characterised and modelled through different urban measures. Consistency within these observables is crucial in order to advance towards a science of cities. Bettencourt et al have proposed that many of these urban measures can be predicted through universal scaling laws. We develop a framework to consistently define cities, using commuting to work and population density thresholds, and construct thousands of realisations of systems of cities with different boundaries for England and Wales. These serve as a laboratory for the scaling analysis of a large set of urban indicators. The analysis shows that population size alone does not provide enough information to describe or predict the state of a city as previously proposed, indicating that the expected scaling laws are not corroborated. We found that most urban indicators scale linearly with city size regardless of the definition of the urban boundaries. However, when non-linear correlations are present, the exponent fluctuates considerably.Comment: Accepted for publication, Journal of the Royal Society Interfac

Developing urban tourism in green infrastructure

Urban tourism depends on the place specific qualities of destinations. In many cities, climate change poses a threat to these qualities, through increasing risk of excessive heat, draught and flooding. Cities need to adapt to reduce these risks. One way of doing this is to improve their green infrastructure. Urban forests, parks, rivers and wetlands may help reduce the effects of climate change in cities. At the same time, green infrastructure provide a variety of ecosystem services to the community. In particular, cultural ecosystem services such as recreation, and esthetical values take place in urban green infrastructure; they provide value in the form of improved experiences. These mainly benefit the locals but they may also be important for tourism. Such relations between ecosystem services and tourism have in earlier literature been recognized in rural contexts but very seldom in urban.This paper reports preliminary findings from qualitative case studies in Malmö, Lund, and Helsingborg in the South of Sweden. They focus on how urban planning projects (primarily aimed at mitigating GHG emissions and adapting to climate change) can be extended to develop places where experience values for both residents and visitors are created alongside other kinds of ecosystem services.We suggest that the need for climate change adaptation in a city may be used as a means to improve its place specific qualities as a tourist destination. By developing green infrastructure in innovative and environmentally friendly ways, the quality of ecosystem services improves, including those relevant for both visitors and residents. Protecting and building green infrastructure, thereby enhancing a city´s visible qualities and its reputation as a sustainable destination, may also be valuable in marketing the city

Predicting Attitudes Towards Transactional Sex: The Interactive Relationship Between Gender and Attitudes on Sexual Behaviour

Introduction: This article explores explanations for attitudes towards the acceptability of transactional sex. The sparse research investigating attitudes towards transactional sex uncovers a link between gender equality, or feminism, and a lack of support for the trade in sex. However, there are no research agendas that attempt to explain variance in attitudes towards transactional sex where support for gender equality is widespread throughout a population. Methods: We estimate regression models utilizing the 2017 Danish Values Survey (Den Danske Værdiundersøgelse) in order to predict views on the acceptability of transactional sex. Results: While the trade in sex is legal in Denmark, we find that a majority of respondents hold negative attitudes towards transactional sex, which conveys a lack of congruence between public opinion and policy. Further, gender is a powerful predictor of attitudes towards transactional sex, with women finding it less acceptable. In addition, the analysis uncovers that general attitudes towards sexual behaviour are the largest predictor of views on the acceptability of transactional sex. That being said, we find that men’s views on the acceptability of transactional sex are more of a function of their general attitudes towards sexual behaviour than they are for women. Conclusions: The findings indicate that, unlike men, women appear to differentiate between their attitudes towards general sexual behaviour and their views on sexual behaviour that they may associate with negative societal implications

D = 5 maximally supersymmetric Yang-Mills theory diverges at six loops

The connection of maximally supersymmetric Yang-Mills theory to the (2,0) theory in six dimensions has raised the possibility that it might be perturbatively ultraviolet finite in five dimensions. We test this hypothesis by computing the coefficient of the first potential ultraviolet divergence of planar (large N_c) maximally supersymmetric Yang-Mills theory in D = 5, which occurs at six loops. We show that the coefficient is nonvanishing. Furthermore, the numerical value of the divergence falls very close to an approximate exponential formula based on the coefficients of the divergences through five loops. This formula predicts the approximate values of the ultraviolet divergence at loop orders L > 6 in the critical dimension D = 4 + 6/L. To obtain the six-loop divergence we first construct the planar six-loop four-point amplitude integrand using generalized unitarity. The ultraviolet divergence follows from a set of vacuum integrals, which are obtained by expanding the integrand in the external momenta. The vacuum integrals are integrated via sector decomposition, using a modified version of the FIESTA program.Comment: 31 pages, revtex, 12 figure

On the non-linearity of the willingness to commute

Established analysis of labour market commuting are based on random choice models and gravity type models. In these models generalised transport costs are formulated as exponential or loglinear distance-dependent functions. This paper presents empirical observations that imply that time-distances influence the commuting behaviour in a non-linear way, such that the time sensitivity is much lower for very short and long distances, whereas intermediate distance display a high time sensitivity. This is explained in a model which is parametrised and estimated. The results are important for understanding and predicting commuter behaviour. It also helps to delineate space, as in classical traditions, into local, intra-regional, and extra-regional space