5 research outputs found
Experimental long-lived entanglement of two macroscopic objects
Entanglement is considered to be one of the most profound features of quantum
mechanics. An entangled state of a system consisting of two subsystems cannot
be described as a product of the quantum states of the two subsystems. In this
sense the entangled system is considered inseparable and nonlocal. It is
generally believed that entanglement manifests itself mostly in systems
consisting of a small number of microscopic particles. Here we demonstrate
experimentally the entanglement of two objects, each consisting of about 10^12
atoms. Entanglement is generated via interaction of the two objects - more
precisely, two gas samples of cesium atoms - with a pulse of light, which
performs a non-local Bell measurement on collective spins of the samples. The
entangled spin state can be maintained for 0.5 millisecond. Besides being of
fundamental interest, the robust, long-lived entanglement of material objects
demonstrated here is expected to be useful in quantum information processing,
including teleportation of quantum states of matter and quantum memory.Comment: Submitted to Nature, June 9, 2001, 11 pages, 3 figures. Contents
changed following referees' suggestion
Multidimensional Scaling Reveals the Main Evolutionary Pathways of Class A G-Protein-Coupled Receptors
Class A G-protein-coupled receptors (GPCRs) constitute the largest family of transmembrane receptors in the human genome. Understanding the mechanisms which drove the evolution of such a large family would help understand the specificity of each GPCR sub-family with applications to drug design. To gain evolutionary information on class A GPCRs, we explored their sequence space by metric multidimensional scaling analysis (MDS). Three-dimensional mapping of human sequences shows a non-uniform distribution of GPCRs, organized in clusters that lay along four privileged directions. To interpret these directions, we projected supplementary sequences from different species onto the human space used as a reference. With this technique, we can easily monitor the evolutionary drift of several GPCR sub-families from cnidarians to humans. Results support a model of radiative evolution of class A GPCRs from a central node formed by peptide receptors. The privileged directions obtained from the MDS analysis are interpretable in terms of three main evolutionary pathways related to specific sequence determinants. The first pathway was initiated by a deletion in transmembrane helix 2 (TM2) and led to three sub-families by divergent evolution. The second pathway corresponds to the differentiation of the amine receptors. The third pathway corresponds to parallel evolution of several sub-families in relation with a covarion process involving proline residues in TM2 and TM5. As exemplified with GPCRs, the MDS projection technique is an important tool to compare orthologous sequence sets and to help decipher the mutational events that drove the evolution of protein families