Strong atom-field coupling for Bose-Einstein condensates in an optical cavity on a chip

An optical cavity enhances the interaction between atoms and light, and the rate of coherent atom-photon coupling can be made larger than all decoherence rates of the system. For single atoms, this 'strong coupling regime' of cavity quantum electrodynamics has been the subject of many experimental advances. Efforts have been made to control the coupling rate by trapping the atom and cooling it towards the motional ground state; the latter has been achieved in one dimension so far. For systems of many atoms, the three-dimensional ground state of motion is routinely achieved in atomic Bose-Einstein condensates (BECs). Although experiments combining BECs and optical cavities have been reported recently, coupling BECs to cavities that are in the strong-coupling regime for single atoms has remained an elusive goal. Here we report such an experiment, made possible by combining a fibre-based cavity with atom-chip technology. This enables single-atom cavity quantum electrodynamics experiments with a simplified set-up and realizes the situation of many atoms in a cavity, each of which is identically and strongly coupled to the cavity mode. Moreover, the BEC can be positioned deterministically anywhere within the cavity and localized entirely within a single antinode of the standing-wave cavity field; we demonstrate that this gives rise to a controlled, tunable coupling rate. We study the heating rate caused by a cavity transmission measurement as a function of the coupling rate and find no measurable heating for strongly coupled BECs. The spectrum of the coupled atoms-cavity system, which we map out over a wide range of atom numbers and cavity-atom detunings, shows vacuum Rabi splittings exceeding 20 gigahertz, as well as an unpredicted additional splitting, which we attribute to the atomic hyperfine structure. We anticipate that the system will be suitable as a light-matter quantum interface for quantum information.     

Systematic screen for human disease genes in yeast

High similarity between yeast and human mitochondria allows functional genomic study of Saccharomyces cerevisiae to be used to identify human genes involved in disease. So far, 102 heritable disorders have been attributed to defects in a quarter of the known nuclear-encoded mitochondrial proteins in humans. Many mitochondrial diseases remain unexplained, however, in part because only 40-60% of the presumed 700-1,000 proteins involved in mitochondrial function and biogenesis have been identified. Here we apply a systematic functional screen using the pre-existing whole-genome pool of yeast deletion mutants to identify mitochondrial proteins. Three million measurements of strain fitness identified 466 genes whose deletions impaired mitochondrial respiration, of which 265 were new. Our approach gave higher selection than other systematic approaches, including fivefold greater selection than gene expression analysis. To apply these advantages to human disorders involving mitochondria, human orthologs were identified and linked to heritable diseases using genomic map positions.     

Attention modulates synchronized neuronal firing in primate somatosensory cortex

A potentially powerful information processing strategy in the brain is to take advantage of the temporal structure of neuronal spike trains. An increase in synchrony within the neural representation of an object or location increases the efficacy of that neural representation at the next synaptic stage in the brain; thus, increasing synchrony is a candidate for the neural correlate of attentional selection. We investigated the synchronous firing of pairs of neurons in the secondary somatosensory cortex (SII) of three monkeys trained to switch attention between a visual task and a tactile discrimination task. We found that most neuron pairs in SII cortex fired synchronously and, furthermore, that the degree of synchrony was affected by the monkey's attentional state. In the monkey performing the most difficult task, 35% of neuron pairs that fired synchronously changed their degree of synchrony when the monkey switched attention between the tactile and visual tasks. Synchrony increased in 80% and decreased in 20% of neuron pairs affected by attention.     

Independent evolution of striated muscles in cnidarians and bilaterians

Striated muscles are present in bilaterian animals (for example, vertebrates, insects and annelids) and some non-bilaterian eumetazoans (that is, cnidarians and ctenophores). The considerable ultrastructural similarity of striated muscles between these animal groups is thought to reflect a common evolutionary origin. Here we show that a muscle protein core set, including a type II myosin heavy chain (MyHC) motor protein characteristic of striated muscles in vertebrates, was already present in unicellular organisms before the origin of multicellular animals. Furthermore, 'striated muscle' and 'non-muscle' myhc orthologues are expressed differentially in two sponges, compatible with a functional diversification before the origin of true muscles and the subsequent use of striated muscle MyHC in fast-contracting smooth and striated muscle. Cnidarians and ctenophores possess striated muscle myhc orthologues but lack crucial components of bilaterian striated muscles, such as genes that code for titin and the troponin complex, suggesting the convergent evolution of striated muscles. Consistently, jellyfish orthologues of a shared set of bilaterian Z-disc proteins are not associated with striated muscles, but are instead expressed elsewhere or ubiquitously. The independent evolution of eumetazoan striated muscles through the addition of new proteins to a pre-existing, ancestral contractile apparatus may serve as a model for the evolution of complex animal cell types.     

Transfer of specificity by murine alpha and beta T-cell receptor genes

T-cell receptor alpha- and beta-chain genes were isolated from a class I major histocompatibility complex-restricted cytotoxic T-cell clone and transferred by protoplast fusion into another cytolytic T-cell clone of different specificity. Expression of the transfected alpha and beta genes endowed the recipient cell with the specificity of the donor cell.     

Transfection of the CD8 gene enhances T-cell recognition

Antibodies against CD8 or CD4 antigens can prevent T-cell functions induced by T-cell targets. As CD8 or CD4 antibodies can also initiate negative signals in T cells in the absence of appropriate targets it is not clear whether CD8 and CD4 molecules are directly involved in the interaction of T cells with their targets. In previous experiments we have introduced the T-cell receptor alpha- and beta-chain genes from a CD8-positive cytolytic T cell specific for the antigen fluorescein (FL) and the H-2D molecule of the major histocompatibility complex (MHC) into a CD8-negative recipient cell. The CD8-positive donor cell lysed both FL-conjugated fibroblasts and lymphoblasts, which express relatively high and low amounts of H-2D molecules, respectively. In contrast the CD8-negative transfectant lysed FL-conjugated fibroblasts only. Here we show that recognition of FL-conjugated lymphoblasts by the transfectant is enhanced by supertransfecting it with the CD8 gene.     

Interleukin-3 supports growth of mouse pre-B-cell clones in vitro

Study of the differentiation of immunoglobulin-producing B lymphocytes has been hampered by the inability to maintain homogeneous populations of precursor cells in vitro. We describe here that interleukin-3 supports the growth of freshly isolated fetal liver pre-B cells and the long-term culture of interleukin-3 dependent pre-B-cell clones that can be induced to mature into antibody secreting cells in vitro.