56 research outputs found
Solitary waves in fluid-filled elastic tubes: existence, persistence, and the role of axial displacement
Four-qubit device with mixed couplings
We present the first experimental results on a device with more than two
superconducting qubits. The circuit consists of four three-junction flux
qubits, with simultaneous ferro- and antiferromagnetic coupling implemented
using shared Josephson junctions. Its response, which is dominated by the
ground state, is characterized using low-frequency impedance measurement with a
superconducting tank circuit coupled to the qubits. The results are found to be
in excellent agreement with the quantum-mechanical predictions.Comment: REVTeX 4, 5pp., 7 EPS figure files. N.B.: "Alec" is my first, and
"Maassen van den Brink" my family name. v2: final published version, with
changed title, different sample micrograph, and several clarification
Degenerate ground state in a mesoscopic YBaCuO grain boundary Josephson junction
We have measured the current-phase relationship (CPR) of symmetric 45 degree
YBaCuO grain boundary Josephson junctions. Substantial deviations of the CPR
from conventional tunnel-junction behavior have been observed: (i) The critical
current exhibits, as a function of temperature T, a local minimum at a
temperature T*. (ii) At T approximately equal to T*, the first harmonic of the
CPR changes sign. (iii) For T<T*, the second harmonic of the CPR is comparable
to the first harmonic, and (iv) the ground state of the junction becomes
degenerate. The results are in good agreement with a microscopic model of
Josephson junctions between d-wave superconductors.Comment: 4 pages, 5 figures, a reference adde
Controllable pi junction in a Josephson quantum-dot device with molecular spin
We consider a model for a single molecule with a large frozen spin sandwiched
in between two BCS superconductors at equilibrium, and show that this system
has a junction behavior at low temperature. The shift can be
reversed by varying the other parameters of the system, e.g., temperature or
the position of the quantum dot level, implying a controllable junction
with novel application as a Josephson current switch. We show that the
mechanism leading to the shift can be explained simply in terms of the
contributions of the Andreev bound states and of the continuum of states above
the superconducting gap. The free energy for certain configuration of
parameters shows a bistable nature, which is a necessary pre-condition for
achievement of a qubit
Josephson effect in d-wave superconductor junctions in a lattice model
Josephson current between two d-wave superconductors is calculated by using a
lattice model. Here we consider two types of junctions, , the parallel
junction and the mirror-type junction. The maximum Josephson current
shows a wide variety of temperature () dependence depending on the
misorientation angles and the types of junctions. When the misorientation
angles are not zero, the Josephson current shows the low-temperature anomaly
because of a zero energy state (ZES) at the interfaces. In the case of
mirror-type junctions, has a non monotonic temperature dependence. These
results are consistent with the previous results based on the quasiclassical
theory. [Y. Tanaka and S. Kashiwaya: Phys. Rev. B \textbf{56} (1997) 892.] On
the other hand, we find that the ZES disappears in several junctions because of
the Freidel oscillations of the wave function, which is peculiar to the lattice
model. In such junctions, the temperature dependence of is close to the
Ambegaokar-Baratoff relation.Comment: 17 pages, 10 figures, using jpsj2.cls and oversite.st
Wideband-tuneable, nanotube mode-locked, fibre laser
Ultrashort-pulse lasers with spectral tuning capability have widespread applications in fields such as spectroscopy, biomedical research and telecommunications1–3. Mode-locked fibre lasers are convenient and powerful sources of ultrashort pulses4, and the inclusion of a broadband saturable absorber as a passive optical switch inside the laser cavity may offer tuneability over a range of wavelengths5. Semiconductor saturable absorber mirrors are widely used in fibre lasers4–6, but their operating range is typically limited to a few tens of nanometres7,8, and their fabrication can be challenging in the 1.3–1.5 mm wavelength region used for optical communications9,10. Single-walled carbon nanotubes are excellent saturable absorbers because of their subpicosecond recovery time, low saturation intensity, polarization insensitivity, and mechanical and environmental robustness11–16. Here, we engineer a nanotube–polycarbonate film with a wide bandwidth (>300 nm) around 1.55 mm, and then use it to demonstrate a 2.4 ps Er31-doped fibre laser that is tuneable from 1,518 to 1,558 nm. In principle, different diameters and chiralities of nanotubes could be combined to enable compact, mode-locked fibre lasers that are tuneable over a much broader range of wavelengths than other systems
Molecular structure of cupric 4-(phosphonomethyl)-2-hydroxy-2-oxo-1, 4,2-oxazaphosphorinane complexonate
Effect of parameters of acoustic stimulation on responses of the auditory nerve in the owlsAsio otus andAthene noctua
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