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Identification of genes influencing dendrite morphogenesis in developing peripheral sensory and central motor neurons.
BACKGROUND: Developing neurons form dendritic trees with cell type-specific patterns of growth, branching and targeting. Dendrites of Drosophila peripheral sensory neurons have emerged as a premier genetic model, though the molecular mechanisms that underlie and regulate their morphogenesis remain incompletely understood. Still less is known about this process in central neurons and the extent to which central and peripheral dendrites share common organisational principles and molecular features. To address these issues, we have carried out two comparable gain-of-function screens for genes that influence dendrite morphologies in peripheral dendritic arborisation (da) neurons and central RP2 motor neurons. RESULTS: We found 35 unique loci that influenced da neuron dendrites, including five previously shown as required for da dendrite patterning. Several phenotypes were class-specific and many resembled those of known mutants, suggesting that genes identified in this study may converge with and extend known molecular pathways for dendrite development in da neurons. The second screen used a novel technique for cell-autonomous gene misexpression in RP2 motor neurons. We found 51 unique loci affecting RP2 dendrite morphology, 84% expressed in the central nervous system. The phenotypic classes from both screens demonstrate that gene misexpression can affect specific aspects of dendritic development, such as growth, branching and targeting. We demonstrate that these processes are genetically separable. Targeting phenotypes were specific to the RP2 screen, and we propose that dendrites in the central nervous system are targeted to territories defined by Cartesian co-ordinates along the antero-posterior and the medio-lateral axes of the central neuropile. Comparisons between the screens suggest that the dendrites of peripheral da and central RP2 neurons are shaped by regulatory programs that only partially overlap. We focused on one common candidate pathway controlled by the ecdysone receptor, and found that it promotes branching and growth of developing da neuron dendrites, but a role in RP2 dendrite development during embryonic and early larval stages was not apparent. CONCLUSION: We identified commonalities (for example, growth and branching) and distinctions (for example, targeting and ecdysone response) in the molecular and organizational framework that underlies dendrite development of peripheral and central neurons.RIGHTS : This article is licensed under the BioMed Central licence at http://www.biomedcentral.com/about/license which is similar to the 'Creative Commons Attribution Licence'. In brief you may : copy, distribute, and display the work; make derivative works; or make commercial use of the work - under the following conditions: the original author must be given credit; for any reuse or distribution, it must be made clear to others what the license terms of this work are
Robust entanglement
It is common belief among physicists that entangled states of quantum systems
loose their coherence rather quickly. The reason is that any interaction with
the environment which distinguishes between the entangled sub-systems collapses
the quantum state. Here we investigate entangled states of two trapped Ca
ions and observe robust entanglement lasting for more than 20 seconds
Low-dimensional quite noisy bound entanglement with cryptographic key
We provide a class of bound entangled states that have positive distillable
secure key rate. The smallest state of this kind is 4 \bigotimes 4. Our class
is a generalization of the class presented in [1] (IEEE Trans. Inf. Theory 54,
2621 (2008); arXiv:quant-ph/0506203). It is much wider, containing, in
particular, states from the boundary of PPT entangled states (all of the states
in the class in [1] were of this kind) but also states inside the set of PPT
entangled states, even, approaching the separable states. This generalization
comes with a price: for the wider class a positive key rate requires, in
general, apart from the one-way Devetak-Winter protocol (used in [1]) also the
recurrence preprocessing and thus effectively is a two-way protocol. We also
analyze the amount of noise that can be admixtured to the states of our class
without losing key distillability property which may be crucial for
experimental realization. The wider class contains key-distillable states with
higher entropy (up to 3.524, as opposed to 2.564 for the class in [1]).Comment: 10 pages, final version for J. Phys. A: Math. Theo
Precision spectroscopy with two correlated atoms
We discuss techniques that allow for long coherence times in laser
spectroscopy experiments with two trapped ions. We show that for this purpose
not only entangled ions prepared in decoherence-free subspaces can be used but
also a pair of ions that are not entangled but subject to the same kind of
phase noise. We apply this technique to a measurement of the electric
quadrupole moment of the 3d D5/2 state of 40Ca+ and to a measurement of the
linewidth of an ultrastable laser exciting a pair of 40Ca+ ions
'Designer atoms' for quantum metrology
Entanglement is recognized as a key resource for quantum computation and
quantum cryptography. For quantum metrology, the use of entangled states has
been discussed and demonstrated as a means of improving the signal-to-noise
ratio. In addition, entangled states have been used in experiments for
efficient quantum state detection and for the measurement of scattering
lengths. In quantum information processing, manipulation of individual quantum
bits allows for the tailored design of specific states that are insensitive to
the detrimental influences of an environment. Such 'decoherence-free subspaces'
protect quantum information and yield significantly enhanced coherence times.
Here we use a decoherence-free subspace with specifically designed entangled
states to demonstrate precision spectroscopy of a pair of trapped Ca+ ions; we
obtain the electric quadrupole moment, which is of use for frequency standard
applications. We find that entangled states are not only useful for enhancing
the signal-to-noise ratio in frequency measurements - a suitably designed pair
of atoms also allows clock measurements in the presence of strong technical
noise. Our technique makes explicit use of non-locality as an entanglement
property and provides an approach for 'designed' quantum metrology
Realization of the quantum Toffoli gate with trapped ions
Algorithms for quantum information processing are usually decomposed into
sequences of quantum gate operations, most often realized with single- and two-
qubit gates[1]. While such operations constitute a universal set for quantum
computation, gates acting on more than two qubits can simplify the
implementation of complex quantum algorithms[2]. Thus, a single three-qubit
operation can replace a complex sequence of two-qubit gates, which in turn
promises faster execution with potentially higher Fidelity. One important
three-qubit operation is the quantum Toffoli gate which performs a NOT
operation on a target qubit depending on the state of two control qubits. Here
we present the first experimental realization of the quantum Toffoli gate in an
ion trap quantum computer. Our implementation is particular effcient as we
directly encode the relevant logic information in the motion of the ion string.
[1] DiVincenzo, D. P. Two-bit gates are universal for quantum computation.
cond-mat/9407022, Phys.Rev. A 51, 1015-1022 (1995). [2] Chiaverini, J. et al.
Realization of quantum error correction. Nature 432, 602-605 (2004).Comment: 11 pages, 2 figure
Design and construction of an optical test bed for LISA imaging systems and tilt-to-length coupling
The laser interferometer space antenna (LISA) is a future space-based interferometric gravitational-wave detector consisting of three spacecraft in a triangular configuration. The interferometric measurements of path length changes between satellites will be performed on optical benches in the satellites. Angular misalignments of the interfering beams couple into the length measurement and represent a significant noise source. Imaging systems will be used to reduce this tilt-to-length coupling.
We designed and constructed an optical test bed to experimentally investigate tilt-to-length coupling. It consists of two separate structures, a minimal optical bench and a telescope simulator. The minimal optical bench comprises the science interferometer where the local laser is interfered with light from a remote spacecraft. In our experiment, a simulated version of this received beam is generated on the telescope simulator. The telescope simulator provides a tilting beam, a reference interferometer and an additional static beam as a phase reference. The tilting beam can either be a flat-top beam or a Gaussian beam. We avoid tilt-to-length coupling in the reference interferometer by using a small photo diode placed at an image of the beam rotation point. We show that the test bed is operational with an initial measurement of tilt-to-length coupling without imaging systems.
Furthermore, we show the design of two different imaging systems whose performance will be investigated in future experiments
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