10,954 research outputs found

    Fractionalization of minimal excitations in integer quantum Hall edge channels

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    A theoretical study of the single electron coherence properties of Lorentzian and rectangular pulses is presented. By combining bosonization and the Floquet scattering approach, the effect of interactions on a periodic source of voltage pulses is computed exactly. When such excitations are injected into one of the channels of a system of two copropagating quantum Hall edge channels, they fractionalize into pulses whose charge and shape reflects the properties of interactions. We show that the dependence of fractionalization induced electron/hole pair production in the pulses amplitude contains clear signatures of the fractionalization of the individual excitations. We propose an experimental setup combining a source of Lorentzian pulses and an Hanbury Brown and Twiss interferometer to measure interaction induced electron/hole pair production and more generally to reconstruct single electron coherence of these excitations before and after their fractionalization.Comment: 18 pages, 10 figures, 1 tabl

    Integer and fractional charge Lorentzian voltage pulses analyzed in the frame of Photon-assisted Shot Noise

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    The periodic injection nn of electrons in a quantum conductor using periodic voltage pulses applied on a contact is studied in the energy and time-domain using shot noise computation in order to make comparison with experiments. We particularly consider the case of periodic Lorentzian voltage pulses. When carrying integer charge, they are known to provide electronic states with a minimal number of excitations, while other type of pulses are all accompanied by an extra neutral cloud of electron and hole excitations. This paper focuses on the low frequency shot noise which arises when the pulse excitations are partitioned by a single scatterer in the framework of the Photo Assisted Shot Noise (PASN) theory. As a unique tool to count the number of excitations carried per pulse, shot noise reveals that pulses of arbitrary shape and arbitrary charge show a marked minimum when the charge is integer. Shot noise spectroscopy is also considered to perform energy-domain characterization of the charge pulses. In particular it reveals the striking asymmetrical spectrum of Lorentzian pulses. Finally, time-domain information is obtained from Hong Ou Mandel like noise correlations when two trains of pulses generated on opposite contacts collide on the scatterer. As a function of the time delay between pulse trains, the noise is shown to measure the electron wavepacket autocorrelation function for integer Lorentzian thanks to electron antibunching. In order to make contact with recent experiments all the calculations are made at zero and finite temperature

    Real time decoherence of Landau and Levitov quasi-particles in quantum Hall edge channels

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    Quantum Hall edge channels at integer filling factor provide a unique test-bench to understand decoherence and relaxation of single electronic excitations in a ballistic quantum conductor. In this Letter, we obtain a full visualization of the decoherence scenario of energy (Landau) and time (Levitov) resolved single electron excitations at filling factor őĹ=2\nu=2. We show that the Landau excitation exhibits a fast relaxation followed by spin-charge separation whereas the Levitov excitation only experiences spin-charge separation. We finally suggest to use Hong-Ou-Mandel type experiments to probe specific signatures of these different scenarios.Comment: 14 pages, 8 figure

    The Next Geminga: Deep Multiwavelength Observations of a Neutron Star Identified with 3EG J1835+5918

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    We describe Chandra, HST, and radio observations that reveal a radio-quiet but magnetospherically active neutron star in the error circle of the high-energy gamma-ray source 3EG J1835+5918, the brightest of the unidentified EGRET sources at high Galactic latitude. A Chandra ACIS-S spectrum of the ultrasoft X-ray source RX J1836.2+5925, suggested by Mirabal & Halpern as the neutron star counterpart of 3EG J1835+5918, requires two components: a blackbody of T~3x10^5 K and a hard tail that can be parameterized as a power law of photon index Gamma~2. An upper limit of d < 800 pc can be derived from the blackbody fit under an assumption of R = 10 km. Deep optical imaging with the HST STIS CCD failed to detect this source to a limit of V > 28.5, thus f_X/f_V > 6000 and d > 250 pc assuming the X-ray fitted temperature for the full surface. Repeated observations with the 76 m Lovell telescope at Jodrell Bank place an upper limit of < 0.1 mJy on the flux density at 1400 MHz for a pulsar with P > 0.1 s, and < 0.25 mJy for a ~10 ms pulsar at the location of RX J1836.2+5925. All of this evidence points to an older, possibly more distant version of the highly efficient gamma-ray pulsar Geminga, as the origin of the gamma-rays from 3EG J1835+5918.Comment: 4 pages, 4 figures, accepted for publication in ApJ Letter

    Robust quantum coherence above the Fermi sea

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    In this paper we present an experiment where we measured the quantum coherence of a quasiparticle injected at a well-defined energy above the Fermi sea into the edge states of the integer quantum Hall regime. Electrons are introduced in an electronic Mach-Zehnder interferometer after passing through a quantum dot that plays the role of an energy filter. Measurements show that above a threshold injection energy, the visibility of the quantum interferences is almost independent of the energy. This is true even for high energies, up to 130~őľ\mueV, well above the thermal energy of the measured sample. This result is in strong contradiction with our theoretical predictions, which instead predict a continuous decrease of the interference visibility with increasing energy. This experiment raises serious questions concerning the understanding of excitations in the integer quantum Hall regime

    Global wellposed problem for the 3-D incompressible anisotropic Navier-Stokes equations

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    In this paper, we consider a global wellposed problem for the 3-D incompressible anisotropic Navier-Stokes equations (\textit{ANS}). In order to do so, we first introduce the scaling invariant Besov-Sobolev type spaces, Bp‚ąí1+2p,1/2B^{-1+\frac{2}{p},{1/2}}_{p} and Bp‚ąí1+2p,1/2(T)B^{-1+\frac{2}{p},{1/2}}_{p}(T), p‚Č•2p\geq2. Then, we prove the global wellposedness for (\textit{ANS}) provided the initial data are sufficient small compared to the horizontal viscosity in some suitable sense, which is stronger than Bp‚ąí1+2p,1/2B^{-1+\frac{2}{p},{1/2}}_{p} norm. In particular, our results imply the global wellposedness of (\textit{ANS}) with high oscillatory initial data.Comment: 39 page

    Electron quantum optics : partitioning electrons one by one

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    We have realized a quantum optics like Hanbury Brown and Twiss (HBT) experiment by partitioning, on an electronic beam-splitter, single elementary electronic excitations produced one by one by an on-demand emitter. We show that the measurement of the output currents correlations in the HBT geometry provides a direct counting, at the single charge level, of the elementary excitations (electron/hole pairs) generated by the emitter at each cycle. We observe the antibunching of low energy excitations emitted by the source with thermal excitations of the Fermi sea already present in the input leads of the splitter, which suppresses their contribution to the partition noise. This effect is used to probe the energy distribution of the emitted wave-packets.Comment: 5 pages, 4 figure

    Evidence for a connection between the gamma-ray and the highest energy cosmic-ray emissions by BL Lacertae objects

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    A set of potentially gamma-ray--loud BL Lac objects is selected by intersecting the EGRET and BL Lac catalogs. Of the resulting 14 objects, eight are found to correlate with arrival directions of ultra--high-energy cosmic rays (UHECRs), with significance of the order of 5 sigma. This suggests that gamma-ray emission can be used as a distinctive feature of those BL Lac objects that are capable of producing UHECR.Comment: 11 pages, 1 figure, version published in APJ Letter

    Phase resolved spectroscopy of the Vela pulsar with XMM-Newton

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    The ~10^4 y old Vela Pulsar represents the bridge between the young Crab-like and the middle-aged rotation powered pulsars. Its multiwavelength behaviour is due to the superposition of different spectral components. We take advantage of the unprecedented harvest of photons collected by XMM-Newton to assess the Vela Pulsar spectral shape and to study the pulsar spectrum as a function of its rotational phase. As for the middle-aged pulsars Geminga, PSR B0656+14 and PSR B1055-52 (the "Three Musketeers"), the phase-integrated spectrum of Vela is well described by a three-component model, consisting of two blackbodies (T_bb1=(1.06+/-0.03)x10^6 K, R_bb1=5.1+/-0.3 km, T_bb2=(2.16+/-0.06)x10^6 K, R_bb2=0.73+/-0.08 km) plus a power-law (gamma=2.2+/-0.3). The relative contributions of the three components are seen to vary as a function of the pulsar rotational phase. The two blackbodies have a shallow 7-9% modulation. The cooler blackbody, possibly related to the bulk of the neutron star surface, has a complex modulation, with two peaks per period, separated by ~0.35 in phase, the radio pulse occurring exactly in between. The hotter blackbody, possibly originating from a hot polar region, has a nearly sinusoidal modulation, with a single, broad maximum aligned with the second peak of the cooler blackbody, trailing the radio pulse by ~0.15 in phase. The non thermal component, magnetospheric in origin, is present only during 20% of the pulsar phase and appears to be opposite to the radio pulse. XMM-Newton phase-resolved spectroscopy unveils the link between the thermally emitting surface of the neutron star and its charge-filled magnetosphere, probing emission geometry as a function of the pulsar rotation. This is a fundamental piece of information for future 3-dimensional modeling of the pulsar magnetosphere.Comment: 27 pages, 9 figures. Accepted for publication in Ap
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