6,787 research outputs found
Effect of ferromagnetic contacts on spin accumulation in an all-metallic lateral spin-valve system: Semiclassical spin drift-diffusion equations
We study the effect of the ferromagnetic (FM) contacts on the spin
accumulation in the lateral spin valve system for the collinear magnetization
configurations. When an additional FM electrode is introduced in the
all-metallic lateral spin-valve system, we find that the transresistance can be
fractionally suppressed or very weakly influenced depending on the position of
the additional FM electrode, and relative magnitudes of contact resistance and
the bulk resistance defined over the spin diffusion length. Nonlocal spin
signals such as nonlocal voltage drop and leakage spin currents are independent
of the magnetization orientation of the additional FM electrode. Even when the
additional contact is nonmagnetic, nonlocal spin signals can be changed by the
spin current leaking into the nonmagnetic electrode.Comment: 13 pages, 1 figure, revised versio
Nearly Deterministic Bell Measurement for Multiphoton Qubits and Its Application to Quantum Information Processing
We propose a Bell measurement scheme by employing a logical qubit in
Greenberger-Horne-Zeilinger (GHZ) entanglement with an arbitrary number of
photons. Remarkably, the success probability of the Bell measurement as well as
teleportation of the GHZ entanglement can be made arbitrarily high using only
linear optics elements and photon on-off measurements as the number of photons
increases. Our scheme outperforms previous proposals using single photon qubits
when comparing the success probabilities in terms of the average photon usages.
It has another important advantage for experimental feasibility that it does
not require photon number resolving measurements. Our proposal provides an
alternative candidate for all-optical quantum information processing.Comment: 7 pages (including supplementary material), 2 figures, to be
published in Phys. Rev. Let
Entangling quantum and classical states of light
Entanglement between quantum and classical objects is of special interest in
the context of fundamental studies of quantum mechanics and potential
applications to quantum information processing. In quantum optics, single
photons are treated as light quanta while coherent states are considered the
most classical among all pure states. Recently, entanglement between a single
photon and a coherent state in a free-traveling field was identified to be a
useful resource for optical quantum information processing. However, it was
pointed out to be extremely difficult to generate such states since it requires
a clean cross-Kerr nonlinear interaction. Here, we devise and experimentally
demonstrate a scheme to generate such hybrid entanglement by implementing a
coherent superposition of two distinct quantum operations. The generated states
clearly show entanglement between the two different types of states. Our work
opens a way to generate hybrid entanglement of a larger size and to develop
efficient quantum information processing using such a new type of qubits.Comment: 9 pages, 4 figure
Scaling laws for the photo-ionisation cross section of two-electron atoms
The cross sections for single-electron photo-ionisation in two-electron atoms
show fluctuations which decrease in amplitude when approaching the
double-ionisation threshold. Based on semiclassical closed orbit theory, we
show that the algebraic decay of the fluctuations can be characterised in terms
of a threshold law as with exponent
obtained as a combination of stability exponents of the triple-collision
singularity. It differs from Wannier's exponent dominating double ionisation
processes. The details of the fluctuations are linked to a set of infinitely
unstable classical orbits starting and ending in the non-regularisable triple
collision. The findings are compared with quantum calculations for a model
system, namely collinear helium.Comment: 4 pages, 1 figur
Chemical Abundance Study of One Red Giant Star in NGC 5694 : A Globular Cluster with Dwarf Spheroidals' Chemical Signature?
We report the abundance analysis of one red giant branch star in the
metal-poor outer halo globular cluster NGC 5694. We obtain [Fe/H] = -1.93,
based on the ionized lines, and our metallicity measurement is in good
agreement with previous estimates. We find that [Ca+Ti/2Fe] and [Cu/Fe] of NGC
5694 are about 0.3 -- 0.4 dex lower than other globular clusters with similar
metallicities, but similar to some LMC clusters and stars in some dwarf
spheroidal galaxies. Differences persist, however, in the abundances of neutron
capture elements. The unique chemical abundance pattern and the large
Galactocentric distance (30 kpc) and radial velocity (-138.6 +/- 1.0 km/sec)
indicate that NGC 5694 had an extragalactic origin.Comment: ApJL accepte
Spin Hall torque magnetometry of Dzyaloshinskii domain walls
Current-induced domain wall motion in the presence of the
Dzyaloshinskii-Moriya interaction (DMI) is experimentally and theoretically
investigated in heavy-metal/ferromagnet bilayers. The angular dependence of the
current-induced torque and the magnetization structure of Dzyaloshinskii domain
walls are described and quantified simultaneously in the presence of in-plane
fields. We show that the DMI strength depends strongly on the heavy metal,
varying by a factor of 20 between Ta and Pa, and that strong DMI leads to wall
distortions not seen in conventional materials. These findings provide
essential insights for understanding and exploiting chiral magnetism for
emerging spintronics applications
Spin relaxation in mesoscopic superconducting Al wires
We studied the diffusion and the relaxation of the polarized quasiparticle
spins in superconductors. To that end, quasiparticles of polarized spins were
injected through an interface of a mesoscopic superconducting Al wire in
proximity contact with an overlaid ferromagnetic Co wire in the single-domain
state. The superconductivity was observed to be suppressed near the
spin-injecting interface, as evidenced by the occurrence of a finite voltage
for a bias current below the onset of the superconducting transition. The spin
diffusion length, estimated from finite voltages over a certain length of Al
wire near the interface, was almost temperature independent in the temperature
range sufficiently below the superconducting transition but grew as the
transition temperature was approached. This temperature dependence suggests
that the relaxation of the spin polarization in the superconducting state is
governed by the condensation of quasiparticles to the paired state. The spin
relaxation in the superconducting state turned out to be more effective than in
the normal state.Comment: 9 pages, 8 figure
EXPERIMENTAL INVESTIGATION OF OPEN LOOP MULTI-STAGE IMPEDANCE PUMPING SYSTEM
Impedance pump is a simple valveless pumping mechanism, where an elastic tube is joined to a more rigid one; a periodic asymmetrical pinching on the elastic tube will produce a unidirectional flow. This pumping concept offers a low energy, low noise alternative at both micro and macro scales. This paper describes an experimental investigation of the performance of a two-stage, open loop impedance pump. The results show that, when compared to a single stage open loop impedance pump, the two-stage impedance pump can achieve a significant pressure head and flow rate increment. A pressure head increment of 240 Pa is obtained in the single stage system compared to 480 Pa for the two-stage system. The corresponding flow rates were 5 mL/s and 8 mL/s respectively. This is an indication that impedance pumping system can be scaled up to achieve a variety of pumping assignments
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