Nonlinear quantum optics in the (ultra)strong light-matter coupling

The propagation of $N$ photons in one dimensional waveguides coupled to $M$ qubits is discussed, both in the strong and ultrastrong qubit-waveguide coupling. Special emphasis is placed on the characterisation of the nonlinear response and its linear limit for the scattered photons as a function of $N$, $M$, qubit inter distance and light-matter coupling. The quantum evolution is numerically solved via the Matrix Product States technique. Both the time evolution for the field and qubits is computed. The nonlinear character (as a function of $N/M$) depends on the computed observable. While perfect reflection is obtained for $N/M \cong 1$, photon-photon correlations are still resolved for ratios $N/M= 2/20$. Inter-qubit distance enhances the nonlinear response. Moving to the ultrastrong coupling regime, we observe that inelastic processes are \emph{robust} against the number of qubits and that the qubit-qubit interaction mediated by the photons is qualitatively modified. The theory developed in this work modelises experiments in circuit QED, photonic crystals and dielectric waveguides.Comment: Comments are wellcom

Choice of Metrics used in Collaborative Filtering and their Impact on Recommender Systems

The capacity of recommender systems to make correct predictions is essentially determined by the quality and suitability of the collaborative filtering that implements them. The common memory-based metrics are Pearson correlation and cosine, however, their use is not always the most appropriate or sufficiently justified. In this paper, we analyze these two metrics together with the less common mean squared difference (MSD) to discover their advantages and drawbacks in very important aspects such as the impact when introducing different values of k-neighborhoods, minimization of the MAE error, capacity to carry out a sufficient number of predictions, percentage of correct and incorrect predictions and behavior when attempting to recommend the n-best items. The paper lists the results and practical conclusions that have been obtained after carrying out a comparative study of the metrics based on 135 experiments on the MovieLens database of 100,000 ratios

Scattering in the ultrastrong regime: nonlinear optics with one photon

The scattering of a flying photon by a two-level system ultrastrongly coupled to a one-dimensional photonic waveguide is studied numerically. The photonic medium is modeled as an array of coupled cavities and the whole system is analyzed beyond the rotating wave approximation using Matrix Product States. It is found that the scattering is strongly influenced by the single- and multi-photon dressed bound states present in the system. In the ultrastrong coupling regime a new channel for inelastic scattering appears, where an incident photon deposits energy into the qubit, exciting a photon-bound state, and escaping with a lower frequency. This single-photon nonlinear frequency conversion process can reach up to 50\% efficiency. Other remarkable features in the scattering induced by counter-rotating terms are a blueshift of the reflection resonance and a Fano resonance due to long-lived excited statesComment: 5+4 page

One- and two-photon scattering from generalized V-type atoms

The one- and two-photon scattering matrix S is obtained analytically for a one-dimensional waveguide and a point-like scatterer with N excited levels (generalized V -type atom). We argue that the two-photon scattering matrix contains sufficient information to distinguish between different level structures which are equivalent for single-photon scattering, such as a V -atom with N = 2 excited levels and two two-level systems. In particular, we show that the scattering with the V -type atom exhibits a destructive interference effect leading to two-photon Coupled-Resonator-Induced Transparency, where the nonlinear part of the two-photon scattering matrix vanishes when each incident photon fulfills a single-photon condition for transparency

Single photons by quenching the vacuum

Heisenberg's uncertainty principle implies that the quantum vacuum is not empty but fluctuates. These fluctuations can be converted into radiation through nonadiabatic changes in the Hamiltonian. Here, we discuss how to control this vacuum radiation, engineering a single-photon emitter out of a two-level system (2LS) ultrastrongly coupled to a finite-band waveguide in a vacuum state. More precisely, we show the 2LS nonlinearity shapes the vacuum radiation into a nonGaussian superposition of even and odd cat states. When the 2LS bare frequency lays within the band gaps, this emission can be well approximated by individual photons. This picture is confirmed by a characterization of the ground and bound states, and a study of the dynamics with matrix product states and polaron Hamiltonian methods.Comment: 9 pages, 10 figure

What is going on in entrepreneurship research? A bibliometric and SNA analysis

Entrepreneurship is a highly dynamic and fast-growing academic research field with a long intellectual tradition. It attracts scholars with different backgrounds and theoretical frameworks, and with different levels of analyses and methodological orientations. But where is the field headed next? What is going on in entrepreneurship research? The purpose of this paper is to take stock of the current research in the field, to map it using bibliometric methods and social network analysis (SNA), and to offer directions for future research. Bibliographic coupling analysis (BCA) is used in this study, due to its ability to unveil current trends and future priorities as they are reflected at the forefront of research (i.e., active research fronts). Data were collected from the WoS, comprising 5,393 peer-reviewed journal articles published in 273 journals and containing 470,262 cited references. The results provide an overall perspective of the research in the field, identifying 16 different research fronts. We believe that this study significantly contributes to the entrepreneurship field by revealing the advancement of the literature and some of the most active research fronts in this domain, providing insights not previously fully grasped or evaluated by previous literature reviews

On the basis of research on ‘green’ in the disciplines of management and business

In this research, we analyze and map the existing literature on ‘green’ in the disciplines of management and business by applying citation, co-citation, and bibliographic coupling analyses, i.e. using bibliometric methods, from two different perspectives: first, identifying and analyzing the works that have had the greatest impact on research and the changes that have taken place in the intellectual structure of this disciplinary area; and second, reviewing the most recent literature to unveil current trends and future priorities as they are reflected at the forefront of research. To carry out the study we used Clarivate Analytics’ Web of Science Core Collection™ (WoS) –in particular, one of its indexes: the Social Sciences Citation Index (SSCI). From this database, 4,888 articles published between 1968 and 2022 were retrieved. The sample period of 55 years was then divided into two sub-periods: 1968–2011 and 2012–2022 to longitudinally examine the data. To the best of our knowledge, no such study has dealt with this field and we believe the outcomes can help coordinate future research efforts

Emergent Causality and the N-photon Scattering Matrix in Waveguide QED

In this work we discuss the emergence of approximate causality in a general setup from waveguide QED -i.e. a one-dimensional propagating field interacting with a scatterer. We prove that this emergent causality translates into a structure for the N-photon scattering matrix. Our work builds on the derivation of a Lieb-Robinson-type bound for continuous models and for all coupling strengths, as well as on several intermediate results, of which we highlight (i) the asymptotic independence of space-like separated wave packets, (ii) the proper definition of input and output scattering states, and (iii) the characterization of the ground state and correlations in the model. We illustrate our formal results by analyzing the two-photon scattering from a quantum impurity in the ultrastrong coupling regime, verifying the cluster decomposition and ground-state nature. Besides, we generalize the cluster decomposition if inelastic or Raman scattering occurs, finding the structure of the S-matrix in momentum space for linear dispersion relations. In this case, we compute the decay of the fluorescence (photon-photon correlations) caused by this S-matrix

Gender representation in english language teaching materials: a descriptive case study

This research explores gender practices in English Language Teaching (ELT) settings, particularly in the Colombian context. While gender dynamics in education environments have been discussed internationally, there is a need for further exploration in Colombia to foster an inclusive society. This qualitative case study with a content analysis methodology observed and reflected on the practices and materials used by two experienced C1-level language teachers in an ELT classroom at a public university in Pereira, Risaralda. Data analysis involved transcribing and categorizing the information collected from the classes observed. It was found that gender practices and stereotypes were presented in the material, however teachers acknowledged these biases and promoted a space for reflection and a critical analysis of the material. On this way the teachers promoted an inclusive space for interaction that intended to diminish the impact of these biases on their classes.Este Proyecto de investigación explora las dinámicas de género en entornos de enseñanza del inglés como lengua extranjera en el contexto colombiano. Aunque se ha debatico ampliamente acerca del tema a nivel internacional, es necesario explorarlo en el contexto colombiano para fomentar una sociedad inclusiva y en paz. Este estudio de caso cualitativo, realizado con una metodología de análisis de contenido, observó y reflexionó sobre las prácticas y materiales utilizados por dos profesores de inglés como lengua extranjera, cuyo nivel de lengua es superior a C1, en un instituto de inglés ubicado en Pereira, Risaralda. El análisis de datos implicó transcribir y categorizar la información recopilada de las clases observadas. Se encontró que las prácticas y estereotipos de género estaban presentes en el material utilizado; sin embargo, los profesores reconocieron estos sesgos y promovieron un espacio de reflexión y análisis crítico del material. De esta manera, los profesores fomentaron un espacio inclusivo de interacción que pretendía disminuir el impacto de estos sesgos en sus clases.PregradoLicenciado(a) en Bilingüismo con Énfasis en InglésTable of Content Abstract............................................................................................................................... 5 Resumen.............................................................................................................................. 6 Statement of the Problem.................................................................................................... 7 Research Question........................................................................................................... 9 General Objective............................................................................................................ 9 Specific Objectives.......................................................................................................... 9 Conceptual Framework....................................................................................................... 9 Discourse....................................................................................................................... 10 Discourse analysis ..................................................................................................... 10 Gender........................................................................................................................... 11 Grammatical Gender.................................................................................................. 11 Gender-Neutral language........................................................................................... 12 Gendered Language................................................................................................... 14 Genderless Language................................................................................................. 16 Gender Identity.......................................................................................................... 17 Gender Stereotypes.................................................................................................... 18 ELT Materials ............................................................................................................... 19 Literature Review.............................................................................................................. 20 Methodology..................................................................................................................... 23 Type of Research........................................................................................................... 24 Type of Study................................................................................................................ 24 Context .......................................................................................................................... 24 Setting............................................................................................................................ 25 Participants.................................................................................................................... 26 Teachers..................................................................................................................... 26 Researchers ............................................................................................................... 26 Data Collection Methods............................................................................................... 27 Sampling.................................................................................................................... 27 Artifacts..................................................................................................................... 28 Data Analysis.................................................................................................................... 29 Ethical Considerations...................................................................................................... 31 Confidentiality............................................................................................................... 31 4 Consent Forms............................................................................................................... 32 Voluntary Participation ................................................................................................. 32 Reducing the Risk of Harm........................................................................................... 33 Findings............................................................................................................................. 33 Gender Stereotypes and their Representation in ESL Classroom Interactions............. 33 Implications....................................................................................................................... 45 Research Implications................................................................................................... 45 Limitations........................................................................................................................ 46 Conclusions....................................................................................................................... 48 References......................................................................................................................... 5