439 research outputs found
Decoherence-protected memory for a single-photon qubit
The long-lived, efficient storage and retrieval of a qubit encoded on a
photon is an important ingredient for future quantum networks. Although systems
with intrinsically long coherence times have been demonstrated, the combination
with an efficient light-matter interface remains an outstanding challenge. In
fact, the coherence times of memories for photonic qubits are currently limited
to a few milliseconds. Here we report on a qubit memory based on a single atom
coupled to a high-finesse optical resonator. By mapping and remapping the qubit
between a basis used for light-matter interfacing and a basis which is less
susceptible to decoherence, a coherence time exceeding 100 ms has been measured
with a time-independant storage-and-retrieval efficiency of 22%. This
demonstrates the first photonic qubit memory with a coherence time that exceeds
the lower bound needed for teleporting qubits in a global quantum internet.Comment: 3 pages, 4 figure
Exchange magnon induced resistance asymmetry in permalloy spin-Hall oscillators
We investigate magnetization dynamics in a spin-Hall oscillator using a direct current measurement as well as conventional microwave spectrum analysis. When the current applies an anti-damping spin-transfer torque, we observe a change in resistance which we ascribe mainly to the excitation of incoherent exchange magnons. A simple model is developed based on the reduction of the effective saturation magnetization, quantitatively explaining the data. The observed phenomena highlight the importance of exchange magnons on the operation of spin-Hall oscillators
Lunar and mars gravity induce similar changes in spinal motor control as microgravity
Introduction: Once more, plans are underway to send humans to the Moon or possibly even to Mars. It is therefore, important to know potential physiological effects of a prolonged stay in space and to minimize possible health risks to astronauts. It has been shown that spinal motor control strategies change during microgravity induced by parabolic flight. The way in which spinal motor control strategies change during partial microgravity, such as that encountered on the Moon and on Mars, is not known. Methods: Spinal motor control measurements were performed during Earth, lunar, Mars, and micro-gravity conditions and two hypergravity conditions of a parabola. Three proxy measures of spinal motor control were recorded: spinal stiffness of lumbar L3 vertebra using the impulse response, muscle activity of lumbar flexors and extensors using surface electromyography, and lumbar curvature using two curvature distance sensors placed at the upper and lower lumbar spine. The participants were six females and six males, with a mean age of 33 years (standard deviation: 7 years). Results: Gravity condition had a statistically significant (Friedmann tests) effect spinal stiffness (p < 0.001); on EMG measures (multifidus (p = 0.047), transversus abdominis (p < 0.001), and psoas (p < 0.001) muscles) and on upper lumbar curvature sensor (p < 0.001). No effect was found on the erector spinae muscle (p = 0.063) or lower curvature sensor (p = 0.170). Post hoc tests revealed a significant increase in stiffness under micro-, lunar-, and Martian gravity conditions (all p's < 0.034). Spinal stiffness decreased under both hypergravity conditions (all p's ≤ 0.012) and decreased during the second hypergravity compared to the first hypergravity condition (p = 0.012). Discussion: Micro-, lunar-, and Martian gravity conditions resulted in similar increases in spinal stiffness, a decrease in transversus abdominis muscle activity, with no change in psoas muscle activity and thus modulation of spinal motor stabilization strategy compared to those observed under Earth's gravity. These findings suggest that the spine is highly sensitive to gravity transitions but that Lunar and Martian gravity are below that required for normal modulation of spinal motor stabilization strategy and thus may be associated with LBP and/or IVD risk without the definition of countermeasures
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Magneto-optical coupling in whispering-gallery-mode resonators
We demonstrate that yttrium iron garnet microspheres support optical
whispering gallery modes similar to those in non-magnetic dielectric materials.
The direction of the ferromagnetic moment tunes both the resonant frequency via
the Voigt effect as well as the degree of polarization rotation via the Faraday
effect. An understanding of the magneto-optical coupling in whispering gallery
modes, where the propagation direction rotates with respect to the
magnetization, is fundamental to the emerging field of cavity optomagnonics.Engineering and Physical Sciences Research Council (Grant IDs: EP/M50693X/1, EP/L027151/1), European Research Council (Grant ID: 648613), Hitachi (research fellowship), Royal Society (University Research Fellowship), Winton programme for the Physics of SustainabilityThis is the author accepted manuscript. The final version is available from the American Physical Society via http://dx.doi.org/10.1103/PhysRevA.92.06384
Thickness dependence study of current-driven ferromagnetic resonance in Y3Fe5O12/heavy metal bilayers
We use ferromagnetic resonance to study the current-induced torques in YIG/heavy metal bilayers. YIG samples with thickness varying from 14.8 nm to 80 nm, with the Pt or Ta thin film on top, are measured by applying a microwave current into the heavy metals and measuring the longitudinal DC voltage generated by both spin rectification and spin pumping. From a symmetry analysis of the FMR lineshape and its dependence on YIG thickness, we deduce that the Oersted field dominates over spin-transfer torque in driving magnetization dynamics
Disorder-quenched Kondo effect in mesosocopic electronic systems
Nonmagnetic disorder is shown to quench the screening of magnetic moments in
metals, the Kondo effect. The probability that a magnetic moment remains free
down to zero temperature is found to increase with disorder strength.
Experimental consequences for disordered metals are studied. In particular, it
is shown that the presence of magnetic impurities with a small Kondo
temperature enhances the electron's dephasing rate at low temperatures in
comparison to the clean metal case. It is furthermore proven that the width of
the distribution of Kondo temperatures remains finite in the thermodynamic
(infinite volume) limit due to wave function correlations within an energy
interval of order , where is the elastic scattering time. When
time-reversal symmetry is broken either by applying a magnetic field or by
increasing the concentration of magnetic impurities, the distribution of Kondo
temperatures becomes narrower.Comment: 17 pages, 7 figures, new results on Kondo effect in quasi-1D wires
added, 6 Refs. adde
A mechanism for the non-Fermi-liquid behavior in CeCu_{6-x}Au_x
We propose an explanation for the recently observed non-Fermi-liquid behavior
of metallic alloys CeCu_{6-x}Au_x: near x=0.1, the specific heat c is
proportional to T \ln (T_0/T) and the resistivity increases linearly with
temperature T over a wide range of T. These features follow from a model in
which three-dimensional conduction electrons are coupled to two-dimensional
critical ferromagnetic fluctuations near the quantum critical point, x_{c}=0.1.
This picture is motivated by the neutron scattering data in the ordered phase
(x=0.2) and is consistent with the observed phase diagram.Comment: 4 pages, LaTeX, 3 figure
Top-Quark Pair Production Beyond Next-to-Leading Order
We report on recent calculations of the differential cross section for
top-quark pair production at hadron colliders. The results are differential
with respect to the top-pair invariant mass and to the partonic scattering
angle. In these calculations, which were carried out by employing
soft-collinear effective theory techniques, we resummed threshold logarithms up
to next-to-next-to-leading logarithmic order. Starting from the differential
cross section, it is possible to obtain theoretical predictions for the
invariant-mass distribution and the total cross section. We summarize here our
results for these observables, and we compare them with the results obtained
from different calculational methods.Comment: Talk presented at Loops and Legs in Quantum Field Theory 2010,
Woerlitz, Germany, April 25-30, 2010. 6 page
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