387 research outputs found
Spectroscopy and critical temperature of diffusive superconducting/ferromagnetic hybrid structures with spin-active interfaces
The description of the proximity effect in superconducting/ferromagnetic
heterostructures requires to use spin-dependent boundary conditions. Such
boundary conditions must take into account the spin dependence of the phase
shifts acquired by electrons upon scattering on the boundaries of ferromagnets.
The present article shows that this property can strongly affect the critical
temperature and the energy dependence of the density of states of diffusive
heterostructures. These effects should allow a better caracterisation of
diffusive superconductor/ferromagnet interfaces.Comment: 12 pages, 6 figures, to be published in Phys. Rev.
Using Spontaneous Emission of a Qubit as a Resource for Feedback Control
Persistent control of a transmon qubit is performed by a feedback protocol
based on continuous heterodyne measurement of its fluorescence. By driving the
qubit and cavity with microwave signals whose amplitudes depend linearly on the
instantaneous values of the quadratures of the measured fluorescence field, we
show that it is possible to stabilize permanently the qubit in any targeted
state. Using a Josephson mixer as a phase-preserving amplifier, it was possible
to reach a total measurement efficiency =35%, leading to a maximum of 59%
of excitation and 44% of coherence for the stabilized states. The experiment
demonstrates multiple-input multiple-output analog Markovian feedback in the
quantum regime.Comment: Supplementary material can be found as an ancillary objec
Superconducting/ferromagnetic diffusive bilayer with a spin-active interface: a numerical study
We calculate the density of states (DOS) in a diffusive
superconducting/ferromagnetic bilayer with a spin-active interface. We use a
self-consistent numerical treatment to make a systematic study of the effects
of the Spin-Dependence of Interfacial Phase Shifts (SDIPS) on the
self-consistent superconducting gap and the DOS. Strikingly, we find that the
SDIPS can induce a double gap structure (DGS) in the DOS of the ferromagnet,
even when the superconducing layer is much thicker than the superconducting
coherence lenght. We thus obtain DOS curves which have interesting similarities
with those of Phys. Rev. Lett. 100, 237002 (2008).Comment: 7 pages, 6 figures, revised versio
Positive cross-correlations due to Dynamical Channel-Blockade in a three-terminal quantum dot
We investigate current fluctuations in a three-terminal quantum dot in the
sequential tunneling regime. In the voltage-bias configuration chosen here, the
circuit is operated like a beam splitter, i.e. one lead is used as an input and
the other two as outputs. In the limit where a double occupancy of the dot is
not possible, a super-Poissonian Fano factor of the current in the input lead
and positive cross-correlations between the current fluctuations in the two
output leads can be obtained, due to dynamical channel-blockade. When a single
orbital of the dot transports current, this effect can be obtained by lifting
the spin-degeneracy of the circuit with ferromagnetic leads or with a magnetic
field. When several orbitals participate in the electronic conduction, lifting
spin-degeneracy is not necessary. In all cases, we show that a super-Poissonian
Fano factor for the input current is not equivalent to positive
cross-correlations between the outputs. We identify the conditions for
obtaining these two effects and discuss possible experimental realizations.Comment: 18 pages, 20 Figures, submitted to Phys. rev.
Nanospintronics with carbon nanotubes
One of the actual challenges of spintronics is the realization of a
spin-transistor allowing to control spin transport through an electrostatic
gate. In this review, we report on different experiments which demonstrate a
gate control of spin transport in a carbon nanotube connected to ferromagnetic
leads. We also discuss some theoretical approaches which can be used to analyze
spin transport in these systems. We emphasize the roles of the gate-tunable
quasi-bound states inside the nanotube and the coherent spin-dependent
scattering at the interfaces between the nanotube and its ferromagnetic
contacts.Comment: 35 pages, 15 figures, some figures in gi
Entanglement and decoherence of a micromechanical resonator via coupling to a Cooper box
We analyse the quantum dynamics of a micromechanical resonator capacitively
coupled to a Cooper box. With appropriate quantum state control of the Cooper
box, the resonator can be driven into a superposition of spatially separated
states. The Cooper box can also be used to probe the environmentally-induced
decoherence of the resonator superposition state.Comment: 4 pages, 3 figure
Sensitive Radio-Frequency Measurements of a Quantum Dot by Tuning to Perfect Impedance Matching
Electrical readout of spin qubits requires fast and sensitive measurements, which are hindered by poor impedance matching to the device. We demonstrate perfect impedance matching in a radio-frequency readout circuit, using voltage-tunable varactors to cancel out parasitic capacitances. An optimized capacitance sensitivity of
1.6
aF
/
√
Hz
is achieved at a maximum source-drain bias of
170
−
μ
V
root-mean-square and with a bandwidth of 18 MHz. Coulomb blockade in a quantum-dot is measured in both conductance and capacitance, and the two contributions are found to be proportional as expected from a quasistatic tunneling model. We benchmark our results against the requirements for single-shot qubit readout using quantum capacitance, a goal that has so far been elusive
Coupling a quantum dot, fermionic leads and a microwave cavity on-chip
We demonstrate a hybrid architecture consisting of a quantum dot circuit
coupled to a single mode of the electromagnetic field. We use single wall
carbon nanotube based circuits inserted in superconducting microwave cavities.
By probing the nanotube-dot using a dispersive read-out in the Coulomb blockade
and the Kondo regime, we determine an electron-photon coupling strength which
should enable circuit QED experiments with more complex quantum dot circuits.Comment: 4 pages, 4 figure
A DNA-Modified Live Vaccine Prime-Boost Strategy Broadens the T-Cell Response and Enhances the Antibody Response against the Porcine Reproductive and Respiratory Syndrome Virus.
The Porcine Reproductive and Respiratory Syndrome Virus (PRRSV) induces reproductive disorders in sows and respiratory illnesses in growing pigs and is considered as one of the main pathogenic agents responsible for economic losses in the porcine industry worldwide. Modified live PRRSV vaccines (MLVs) are very effective vaccine types against homologous strains but they present only partial protection against heterologous viral variants. With the goal to induce broad and cross-protective immunity, we generated DNA vaccines encoding B and T antigens derived from a European subtype 1 strain that include T-cell epitope sequences known to be conserved across strains. These antigens were expressed either in a native form or in the form of vaccibodies targeted to the endocytic receptor XCR1 and CD11c expressed by different types of antigen-presenting cells (APCs). When delivered in skin with cationic nanoparticles and surface electroporation, multiple DNA vaccinations as a stand-alone regimen induced substantial antibody and T-cell responses, which were not promoted by targeting antigens to APCs. Interestingly, a DNA-MLV prime-boost strategy strongly enhanced the antibody response and broadened the T-cell responses over the one induced by MLV or DNA-only. The anti-nucleoprotein antibody response induced by the DNA-MLV prime-boost was clearly promoted by targeting the antigen to CD11c and XCR1, indicating a benefit of APC-targeting on the B-cell response. In conclusion, a DNA-MLV prime-boost strategy, by enhancing the potency and breadth of MLV vaccines, stands as a promising vaccine strategy to improve the control of PRRSV in infected herds
Is treatment of Segond fracture necessary with combined anterior cruciate ligament reconstruction? Letter to the Editor
Germanium nanowires (NWs) have attractive properties for a variety of applications, including micro- and optoelectronics, memory devices, solar energy conversion, and energy storage, among others. For applications that involve exposure to air, the poor chemical stability and electronic surface passivation of native oxides have remained a long-standing concern. Termination by sulfur-rich surface layers has emerged as a promising strategy for passivation of planar Ge surfaces. Here we discuss experiments on solid-state sulfurization of Ge nanowires in sulfur vapor at near-ambient pressures and at different temperatures. Combined transmission electron microscopy imaging and chemical mapping establishes that Ge NWs remain intact during vapor-phase reaction with S at elevated temperatures, and show the formation of sulfur-rich shells with T-dependent morphology and thickness on the Ge NW surface. Photoluminescence of ensembles of such core-shell nanowires is dominated by strong emission at approximate to 1.85 eV, consistent with luminescence of GeS. Cathodoluminescence spectroscopy on individual NWs establishes that this luminescence originates in thin GeS shells formed by sulfurization of the NWs. Our work establishes direct sulfurization as a viable approach for forming stable, wide-bandgap surface terminations on Ge NWs
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