Camparison of the Hanbury Brown-Twiss effect for bosons and fermions

Fifty years ago, Hanbury Brown and Twiss (HBT) discovered photon bunching in light emitted by a chaotic source, highlighting the importance of two-photon correlations and stimulating the development of modern quantum optics . The quantum interpretation of bunching relies upon the constructive interference between amplitudes involving two indistinguishable photons, and its additive character is intimately linked to the Bose nature of photons. Advances in atom cooling and detection have led to the observation and full characterisation of the atomic analogue of the HBT effect with bosonic atoms. By contrast, fermions should reveal an antibunching effect, i.e., a tendency to avoid each other. Antibunching of fermions is associated with destructive two-particle interference and is related to the Pauli principle forbidding more than one identical fermion to occupy the same quantum state. Here we report an experimental comparison of the fermion and the boson HBT effects realised in the same apparatus with two different isotopes of helium, 3He (a fermion) and 4He (a boson). Ordinary attractive or repulsive interactions between atoms are negligible, and the contrasting bunching and antibunching behaviours can be fully attributed to the different quantum statistics. Our result shows how atom-atom correlation measurements can be used not only for revealing details in the spatial density, or momentum correlations in an atomic ensemble, but also to directly observe phase effects linked to the quantum statistics in a many body system. It may thus find applications to study more exotic situations >.Comment: Nature 445, 402 (2007). V2 includes the supplementary informatio

Quantum Measurement Theory in Gravitational-Wave Detectors

The fast progress in improving the sensitivity of the gravitational-wave (GW) detectors, we all have witnessed in the recent years, has propelled the scientific community to the point, when quantum behaviour of such immense measurement devices as kilometer-long interferometers starts to matter. The time, when their sensitivity will be mainly limited by the quantum noise of light is round the corner, and finding the ways to reduce it will become a necessity. Therefore, the primary goal we pursued in this review was to familiarize a broad spectrum of readers with the theory of quantum measurements in the very form it finds application in the area of gravitational-wave detection. We focus on how quantum noise arises in gravitational-wave interferometers and what limitations it imposes on the achievable sensitivity. We start from the very basic concepts and gradually advance to the general linear quantum measurement theory and its application to the calculation of quantum noise in the contemporary and planned interferometric detectors of gravitational radiation of the first and second generation. Special attention is paid to the concept of Standard Quantum Limit and the methods of its surmounting.Comment: 147 pages, 46 figures, 1 table. Published in Living Reviews in Relativit

Photon-Atom Coupling with Parabolic Mirrors

Efficient coupling of light to single atomic systems has gained considerable attention over the past decades. This development is driven by the continuous growth of quantum technologies. The efficient coupling of light and matter is an enabling technology for quantum information processing and quantum communication. And indeed, in recent years much progress has been made in this direction. But applications aside, the interaction of photons and atoms is a fundamental physics problem. There are various possibilities for making this interaction more efficient, among them the apparently 'natural' attempt of mode-matching the light field to the free-space emission pattern of the atomic system of interest. Here we will describe the necessary steps of implementing this mode-matching with the ultimate aim of reaching unit coupling efficiency. We describe the use of deep parabolic mirrors as the central optical element of a free-space coupling scheme, covering the preparation of suitable modes of the field incident onto these mirrors as well as the location of an atom at the mirror's focus. Furthermore, we establish a robust method for determining the efficiency of the photon-atom coupling.Comment: Book chapter in compilation "Engineering the Atom-Photon Interaction" published by Springer in 2015, edited by A. Predojevic and M. W. Mitchell, ISBN 9783319192307, http://www.springer.com/gp/book/9783319192307. Only change to version1: now with hyperlinks to arXiv eprints of other book chapters mentioned in this on

Drug discovery: Insights from the invertebrate Caenorhabditis elegans

Therapeutic drug development is a long, expensive, and complex process that usually takes 12–15 years. In the early phases of drug discovery, in particular, there is a growing need for animal models that ensure the reduction in both cost and time. Caenorhabditis elegans has been traditionally used to address fundamental aspects of key biological processes, such as apoptosis, aging, and gene expression regulation. During the last decade, with the advent of large-scale platforms for screenings, this invertebrate has also emerged as an essential tool in the pharmaceutical research industry to identify novel drugs and drug targets. In this review, we discuss the reasons why C. elegans has been positioned as an outstanding cost-effective option for drug discovery, highlighting both the advantages and drawbacks of this model. Particular attention is paid to the suitability of this nematode in large-scale genetic and pharmacological screenings. High-throughput screenings in C. elegans have indeed contributed to the breakthrough of a wide variety of candidate compounds involved in extensive fields including neurodegeneration, pathogen infections and metabolic disorders. The versatility of this nematode, which enables its instrumentation as a model of human diseases, is another attribute also herein underscored. As illustrative examples, we discuss the utility of C. elegans models of both human neurodegenerative diseases and parasitic nematodes in the drug discovery industry. Summing up, this review aims to demonstrate the impact of C. elegans models on the drug discovery pipeline.Fil: Giunti, Sebastián. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Investigaciones Bioquímicas de Bahía Blanca. Universidad Nacional del Sur. Instituto de Investigaciones Bioquímicas de Bahía Blanca; Argentina. Universidad Nacional del Sur. Departamento de Biología, Bioquímica y Farmacia; ArgentinaFil: Andersen, Natalia Denise. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Investigaciones Bioquímicas de Bahía Blanca. Universidad Nacional del Sur. Instituto de Investigaciones Bioquímicas de Bahía Blanca; Argentina. Universidad Nacional del Sur. Departamento de Biología, Bioquímica y Farmacia; ArgentinaFil: Rayes, Diego Hernán. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Investigaciones Bioquímicas de Bahía Blanca. Universidad Nacional del Sur. Instituto de Investigaciones Bioquímicas de Bahía Blanca; Argentina. Universidad Nacional del Sur. Departamento de Biología, Bioquímica y Farmacia; ArgentinaFil: de Rosa, Maria Jose. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Investigaciones Bioquímicas de Bahía Blanca. Universidad Nacional del Sur. Instituto de Investigaciones Bioquímicas de Bahía Blanca; Argentina. Universidad Nacional del Sur. Departamento de Biología, Bioquímica y Farmacia; Argentin

Aberrant semantic activation in schizophrenia: a neurophysiological study

OBJECTIVE: Schizophrenia has long been thought to be characterized by a fundamental disturbance in semantic associations, which has often been presumed to be of neurobiological origin. The authors examined the neurophysiological characteristics of semantic processing in schizophrenic patients. METHOD: During EEG recording, 15 schizophrenic patients and 15 age-matched comparison subjects read sentences that had either sensible or nonsensical endings. The authors recorded the N400 component, a specific negative event-related brain potential occurring approximately 400 msec after the final word in the sentence. N400 is highly, if not uniquely, sensitive to semantic expectancy and context, and larger, more negative N400 amplitude is associated with increased semantic unexpectancy. RESULTS: In relation to the normal comparison subjects, the schizophrenic patients demonstrated prolonged N400 latency after nonsensical sentence endings and also showed enhanced N400 negativity, regardless of the sense of the sentence ending. CONCLUSIONS: These findings suggest slower and more diffuse semantic activation in patients with schizophrenia, perhaps reflective of a disease-related failure to maintain and to use semantic context

Quality control methods for herbal medicines

Quality control activities in industry and practice are fundamental in maintaining the safety and efficacy of complementary medicines for customer and patient usage. Internationally, however, there is still great variation and inconsistency of active components in herbal medicines. In order to address these issues, there is an urgent need to develop internationally recognised facilities and methods of quality control for herbal medicines. This review covers the multiple interdisciplinary nature of quality control, including study of traditional Chinese medicine practises, the development in pharmacognosy and the respective analytical methods for fingerprint and quality standardisation of herbal medicines. A combination of these analytical methods will therefore provide a quality control framework for the evaluation of all herbal medicines

A common set of engulfment genes mediates removal of both apoptotic and necrotic cell corpses in C. elegans.

Similar to mammalian excitotoxic cell death, necrotic-like cell death (NCD) in Caenorhabditis elegans can be initiated by hyperactive ion channels. Here we investigate the requirements for genes that execute and regulate programmed cell death (PCD) in necrotic-like neuronal death caused by a toxic MEC-4 channel. Neither the kinetics of necrosis onset nor the total number of necrotic corpses generated is altered by any C. elegans mutation known to block PCD, which provides genetic evidence that the activating mechanisms for NCD and apoptotic cell death are distinct. In contrast, all previously reported ced genes required for phagocytotic removal of apoptotic corpses, as well as ced-12, a new engulfment gene we have identified, are required for efficient elimination of corpses generated by distinct necrosis-inducing stimuli. Our results show that a common set of genes acts to eliminate cell corpses irrespective of the mode of cell death, and provide the first identification of the C. elegans genes that are required for orderly removal of necrotic cells. As phagocytotic mechanisms seem to be conserved from nematodes to humans, our findings indicate that injured necrotic cells in higher organisms might also be eliminated before lysis through a controlled process of corpse removal, a hypothesis that has significant therapeutic implications