Quantum Random Number Generator using Photon-Number Path Entanglement

We report a novel quantum random number generator based on the photon-number$-$path entangled state which is prepared via two-photon quantum interference at a beam splitter. The randomness in our scheme is of truly quantum mechanical origin as it comes from the projection measurement of the entangled two-photon state. The generated bit sequences satisfy the standard randomness test

Heralded generation of entangled photon pairs

Entangled photons are a crucial resource for quantum communication and linear optical quantum computation. Unfortunately, the applicability of many photon-based schemes is limited due to the stochastic character of the photon sources. Therefore, a worldwide effort has focused in overcoming the limitation of probabilistic emission by generating two-photon entangled states conditioned on the detection of auxiliary photons. Here we present the first heralded generation of photon states that are maximally entangled in polarization with linear optics and standard photon detection from spontaneous parametric down-conversion. We utilize the down-conversion state corresponding to the generation of three photon pairs, where the coincident detection of four auxiliary photons unambiguously heralds the successful preparation of the entangled state. This controlled generation of entangled photon states is a significant step towards the applicability of a linear optics quantum network, in particular for entanglement swapping, quantum teleportation, quantum cryptography and scalable approaches towards photonics-based quantum computing

Linear Optical Quantum Computing in a Single Spatial Mode

We present a scheme for linear optical quantum computing using time-bin encoded qubits in a single spatial mode. We show methods for single-qubit operations and heralded controlled phase (CPhase) gates, providing a sufficient set of operations for universal quantum computing with the Knill-Laflamme-Milburn scheme. Our scheme is suited to available photonic devices and ideally allows arbitrary numbers of qubits to be encoded in the same spatial mode, demonstrating the potential for time-frequency modes to dramatically increase the quantum information capacity of fixed spatial resources. As a test of our scheme, we demonstrate the first entirely single spatial mode implementation of a two-qubit quantum gate and show its operation with an average fidelity of 0.84+-0.07.Comment: 5 pages, 4 figures. Updated to be consistent with the published versio

Insights into iguanodontian dental architecture from an Early Cretaceous Chinese basal hadrosauriform maxilla (Ornithischia: Iguanodontia)

Basal hadrosauriform iguanodontian dinosaurs have been invaluable towards understanding the evolution of the complex and highly efficient advanced hadrosauriform tooth battery dental system. Here we report a new basal hadrosauriform maxilla specimen - IVPP V22529 - from the Dashuiguo Formation of Maortu, Nei Mongol, China that preserves a corrugated middle ventrolateral margin that differs from the straight and undulating ventral margins found in most iguandontian and non-iguanodontian dinosaurs. The uniqueness of this ventrolateral margin relates to a new dental structure - cementum ‘jackets’ that wrap about the labial sides of the teeth. To our knowledge this is the first time that cementum has been described migrated onto the tooth crowns of iguandontians (and other dinosaurs), but this trait is common amongst mammals. This dental morphology - seen in a similar form in the basal hadrosauriform Equijubus – therefore broadens our knowledge of iguanodontian maxillary anatomy and shows that the basal hadrosauriform dental system was more morphologically complex than previously thought. IVPP V22529 resembles maxillae specimens of Probactrosaurus gobiensis, a contemporaneous taxon known from the same locality in North China, in sharing an inferred subtriangular shape, a relatively flat lateral surface bearing a low row of foramina as well as similar-looking teeth. However, the presence of a unique corrugated middle ventrolateral margin in IVPP V22529, a low row of foramina on its lateral surface that also open anteriorly and increase in size posteriorly as well as a prominent medial shelf suggests that this specimen does not belong to P. gobiensis. However, these differences could conceivably be related to ontogenetic and sexual variation, which have not been fully documented in P. gobiensis. More detailed comparisons of IVPP V22529 and Probactrosaurus are also hampered by the missing posterior portion of IVPP V22529 as well as the missing anterior ramii in Probactrosaurus maxillae specimens. It is clear though that IVPP V22529 is different from the more advanced Northern Chinese hadrosauriforms Bactrosaurus and Gilmoreosaurus. The latter lack well-developed maxillary grooves on their medial shelves, unlike IVPP V22529, but all three taxa possess less-developed ones on the medial surfaces of the anteromedial processes of the anterior ramii. Different to IVPP V22529, Gilmoreosaurus also has foramina that are more highly-positioned on the lateral surface of its maxilla as well as a row of larger and more circular ‘special’ foramina on its medial surface. Thus, at this time, IVPP V22529 is identified as a basal hadrosauriform and not as a new genus or as a new species of Probactrosaurus.published_or_final_versio

Reducing multi-photon rates in pulsed down-conversion by temporal multiplexing

We present a simple technique to reduce the emission rate of higher-order photon events from pulsed spontaneous parametric down-conversion. The technique uses extra-cavity control over a mode locked ultrafast laser to simultaneously increase repetition rate and reduce the energy of each pulse from the pump beam. We apply our scheme to a photonic quantum gate, showing improvements in the non-classical interference visibility for 2-photon and 4-photon experiments, and in the quantum-gate fidelity and entangled state production in the 2-photon case.Comment: 8 pages, 6 figure

Osteology of the alvarezsauroid Linhenykus monodactylus from the Upper Cretaceous Wulansuhai Formation of Inner Mongolia, China, and comments on alvarezsauroid biogeography

published_or_final_versio

Genetic dissection of dopaminergic and noradrenergic contributions to catecholaminergic tracts in early larval zebrafish

The catecholamines dopamine and noradrenaline provide some of the major neuromodulatory systems with far-ranging projections in the brain and spinal cord of vertebrates. However, development of these complex systems is only partially understood. Zebrafish provide an excellent model for genetic analysis of neuronal specification and axonal projections in vertebrates. Here, we analyze the ontogeny of the catecholaminergic projections in zebrafish embryos and larvae up to the fifth day of development and establish the basic scaffold of catecholaminergic connectivity. The earliest dopaminergic diencephalospinal projections do not navigate along the zebrafish primary neuron axonal scaffold but establish their own tracts at defined ventrolateral positions. By using genetic tools, we study quantitative and qualitative contributions of noradrenergic and defined dopaminergic groups to the catecholaminergic scaffold. Suppression of Tfap2a activity allows us to eliminate noradrenergic contributions, and depletion of Otp activity deletes mammalian A11-like Otp-dependent ventral diencephalic dopaminergic groups. This analysis reveals a predominant contribution of Otp-dependent dopaminergic neurons to diencephalospinal as well as hypothalamic catecholaminergic tracts. In contrast, noradrenergic projections make only a minor contribution to hindbrain and spinal catecholaminergic tracts. Furthermore, we can demonstrate that, in zebrafish larvae, ascending catecholaminergic projections to the telencephalon are generated exclusively by Otp-dependent diencephalic dopaminergic neurons as well as by hindbrain noradrenergic groups. Our data reveal the Otp-dependent A11-type dopaminergic neurons as the by far most prominent dopaminergic system in larval zebrafish. These findings are consistent with a hypothesis that Otp-dependent dopaminergic neurons establish the major modulatory system for somatomotor and somatosensory circuits in larval fish. J. Comp. Neurol. 518:439–458, 2010. © 2009 Wiley-Liss, Inc

Vaccination with DNA plasmids expressing Gn coupled to C3d or alphavirus replicons expressing Gn protects mice against rift valley fever virus

Background: Rift Valley fever (RVF) is an arthropod-borne viral zoonosis. Rift Valley fever virus (RVFV) is an important biological threat with the potential to spread to new susceptible areas. In addition, it is a potential biowarfare agent. Methodology/Principal Findings: We developed two potential vaccines, DNA plasmids and alphavirus replicons, expressing the Gn glycoprotein of RVFV alone or fused to three copies of complement protein, C3d. Each vaccine was administered to mice in an all DNA, all replicon, or a DNA prime/replicon boost strategy and both the humoral and cellular responses were assessed. DNA plasmids expressing Gn-C3d and alphavirus replicons expressing Gn elicited high titer neutralizing antibodies that were similar to titers elicited by the live-attenuated MP12 virus. Mice vaccinated with an inactivated form of MP12 did elicit high titer antibodies, but these antibodies were unable to neutralize RVFV infection. However, only vaccine strategies incorporating alphavirus replicons elicited cellular responses to Gn. Both vaccines strategies completely prevented weight loss and morbidity and protected against lethal RVFV challenge. Passive transfer of antisera from vaccinated mice into naïve mice showed that both DNA plasmids expressing Gn-C3d and alphavirus replicons expressing Gn elicited antibodies that protected mice as well as sera from mice immunized with MP12. Conclusion/Significance: These results show that both DNA plasmids expressing Gn-C3d and alphavirus replicons expressing Gn administered alone or in a DNA prime/replicon boost strategy are effective RVFV vaccines. These vaccine strategies provide safer alternatives to using live-attenuated RVFV vaccines for human use. © 2010 Bhardwaj et al

Adding control to arbitrary unknown quantum operations

While quantum computers promise significant advantages, the complexity of quantum algorithms remains a major technological obstacle. We have developed and demonstrated an architecture-independent technique that simplifies adding control qubits to arbitrary quantum operations-a requirement in many quantum algorithms, simulations and metrology. The technique is independent of how the operation is done, does not require knowledge of what the operation is, and largely separates the problems of how to implement a quantum operation in the laboratory and how to add a control. We demonstrate an entanglement-based version in a photonic system, realizing a range of different two-qubit gates with high fidelity.Comment: 9 pages, 8 figure