Photon-pair generation by non-instantaneous spontaneous four-wave mixing

We present a general model, based on a Hamiltonian approach, for the joint quantum state of photon pairs generated through pulsed spontaneous four-wave mixing, including nonlinear phase-modulation and a finite material response time. For the case of a silica fiber, it is found that the pair-production rate depends weakly on the waveguide temperature, due to higher-order Raman scattering events, and more strongly on pump-pair frequency detuning. From the analytical model, a numerical scheme is derived, based on the well-known split-step method. This scheme allows computation of joint states where nontrivial effects are included, such as group-velocity dispersion and Raman scattering. In this work, the numerical model is used to study the impact of the non-instantaneous response on the pre-filtering purity of heralded single photons. We find that for pump pulses shorter than 1 ps, a significant detuning-dependent change in quantum-mechanical purity may be observed in silica

Engineering spectrally unentangled photon pairs from nonlinear microring resonators through pump manipulation

The future of integrated quantum photonics relies heavily on the ability to engineer refined methods for preparing the quantum states needed to implement various quantum protocols. An important example of such states are quantum-correlated photon pairs, which can be efficiently generated using spontaneous nonlinear processes in integrated microring-resonator structures. In this work, we propose a method for generating spectrally unentangled photon pairs from a standard microring resonator. The method utilizes interference between a primary and a delayed secondary pump pulse to effectively increase the pump spectral width inside the cavity. This enables on-chip generation of heralded single photons with state purities in excess of 99 % without spectral filtering.Comment: 5 pages, 5 figure

Homemade artificial insemination in Spain: Legal and ethical issues

La inseminación artificial casera es una práctica que está experimentando un aumento considerable durante los últimos años debido a las posibilidades que brindan las nuevas tecnologías (especialmente internet), y que ha pasado inadvertida por la práctica totalidad de la doctrina jurídica de nuestro país. Esta técnica suscita numerosas cuestiones acerca de su legalidad y el tratamiento que debe recibir conforme al ordenamiento español, y en particular, conforme a la Ley 14/2006, de 26 de mayo, sobre técnicas de reproducción humana asistida, y su concepción como derecho reproductivoHomemade artificial insemination is a practice that is experiencing a significant increase in recent years due to possibilities provided by new technologies (especially internet), and that has gone unnoticed by most of the legal academics in our country. This technique gives rise to numerous questions about its legal status and the treatment that it must receive according to the Spanish legal system, and particularly, according to the Act 14/2006, from May 26th, on Assisted Human Reproduction Techniques, and its conception as a reproductive right

Cautious Romantics: Trinitarian Transcendentalists and the emergence of a conservative religious tradition in America

The American Transcendentalists are often equated with Romanticism in nineteenth-century America. This dissertation thoroughly complicates that equation, arguing that a group of "Cautious Romantics" emerged as an alternative and conservative Romantic religious tradition. Drawing on history, art history, philosophy, literature, and theology, this dissertation provides a much fuller picture of the way European Romantic texts and authors functioned in American intellectual, cultural, and religious history by highlighting the contribution of these Cautious Romantics. Taken together, the Cautious Romantics represented a distinct religious discourse. They were American Romantics: relentless and introspective questers who emphasized epistemological intuition, artistic inspiration, and spiritual experience. In fact, some of them were the first Americans to promote European Romantic influences. Nevertheless, the Cautious Romantics continued to embrace Trinitarian Christianity, and they celebrated institutions--colleges and churches--in contrast to the often anti-institutional temperament of the Transcendentalists. Moreover, the Cautious Romantics defied religious categorization among standard antebellum groups. They were neither evangelicals, nor traditional Congregationalists, nor Unitarians. Although many became Episcopalians or Catholics, their Romantic intellectual lineage and historical relationships with one another distinguished them from their denominational kindred. Functioning on two levels, this dissertation resituates several well-known American artists and intellectuals such as Washington Allston, Orestes Brownson, Richard Henry Dana Jr., and Harriet Beecher Stowe by connecting them historically and intellectually with a wider discourse. This dissertation also unearths or re-contextualizes numerous lesser-known religious intellectuals such as Richard Henry Dana Sr., James Marsh, Sophia Dana Ripley, George Allen, Henry Hope Reed, Gulian Verplanck, Leonard Woods Jr., and Isaac Hecker. While conservative, these intellectuals were neither committed to the antebellum American South's unique conservative vision nor did they celebrate the free-market conservatism common in twentieth-century America. Thus, in addition to its contribution to intellectual and religious history, this dissertation contributes to a growing body of literature on cultural conservatism in America. Moreover, although the Cautious Romantics were American, this dissertation highlights the important historical relationships between the Cautious Romantics and Coleridge, Wordsworth, the Roman Catholic Church, and, in Harriet Beecher Stowe's case, transatlantic social reform, thereby demonstrating the transatlantic nature of Romanticism in the nineteenth century

Stepwise incorporation of white clover (Trifolium repens L.)as fertiliser increases nitrogen fixation and improves nitrogen retention when intercropped with leek (Allium porrum L.)

Background and aims We investigated whether the incorporation of intercropped white clover as a split-dose fertiliser improves N retention of the plant-soil system in leek production. Methods White clover and leek were grown in pots where clover was stepwise incorporated into soil as fertiliser. Half of the clover was incorporated before leek transplantation (LT), the other half was incorporated 26 (S1) or 41 (S2) days after LT, compared with full incorporation of all clover (F) before LT. 15N injection and leaching studies were performed to investigate interspecific competition and the effects of precipitation on soil N availability. Results Stepwise incorporations increased or had no effect on leek growth, despite competition for N between white clover and leek. Compared to F, leek grown with stepwise incorporations had similar and lower N accumulation before the second incorporation, but N was higher at the end of the experiment. N2 fixation by white clover increased the total N input into soil and matched N availability with leek N demand and growth rate. Loss of inorganic N by leaching was lowest in S2 and highest in F. Conclusions Stepwise incorporations of white clover improved N retention in the plant-soil system and could be used to increase leek yield

Shape-preserving and unidirectional frequency conversion using four-wave mixing Bragg scattering

In this work, we investigate the properties of four-wave mixing Bragg scattering in a configuration that employs orthogonally polarized pumps in a birefringent waveguide. This configuration enables a large signal conversion bandwidth, and allows strongly unidirectional frequency conversion as undesired Bragg-scattering processes are suppressed by waveguide birefringence. Moreover, we show that this form of four-wave mixing Bragg scattering preserves the (arbitrary) signal pulse shape, even when driven by pulsed pumps.Comment: 11 pages + refs, 5 figure

Note to Self: Stop Calling Interfaces “Natural”

The term “natural” is employed to describe a wide range of novel interactive products and systems, ranging from ges- ture-based interaction to brain-computer interfaces and in marketing as well as in research. However, this terminology is problematic. It establishes an untenable dichotomy be- tween forms of interaction that are natural and those that are not; it draws upon the positive connotations of the term and conflates the language of research with marketing lingo, often without a clear explanation of why novel interfaces can be considered natural; and it obscures the examination of the details of interaction that ought to be the concern of HCI researchers. We are primarily concerned with identify- ing the problem, but also propose two steps to remedy it: recognising that the terminology we employ in research has consequences, and unfolding and articulating in more detail the qualities of interfaces that we have hitherto labelled “natural”.