2,695 research outputs found
Conductance fluctuations in a quantum dot under almost periodic ac pumping
It is shown that the variance of the linear dc conductance fluctuations in an
open quantum dot under a high-frequency ac pumping depends significantly on the
spectral content of the ac field. For a sufficiently strong ac field
, where is the dephasing rate induced by
ac noise and is the electron escape rate, the dc conductance
fluctuations are much stronger for the harmonic pumping than in the case of the
noise ac field of the same intensity. The reduction factor in a static
magnetic field takes the universal value of 2 only for the white--noise
pumping. For the strictly harmonic pumping of
sufficiently large intensity the variance is almost insensitive to the static
magnetic field . For the quasi-periodic ac
field of the form with
and we predict the novel
effect of enchancement of conductance fluctuations at commensurate frequencies
.Comment: 4 pages RevTex, 4 eps figures; the final version to appear in
Phys.Rev.
Tissue-Engineered Vascular Graft of Small Diameter Based on Electrospun Polylactide Microfibers
Tubular vascular grafts 1.1 mm in diameter based on poly(L-lactide) microfibers were obtained by electrospinning. X-ray diffraction and scanning electron microscopy data demonstrated that the samples treated at T=70°C for 1 h in the fixed state on a cylindrical mandrel possessed dense fibrous structure; their degree of crystallinity was approximately 44%. Strength and deformation stability of these samples were higher than those of the native blood vessels; thus, it was possible to use them in tissue engineering as bioresorbable vascular grafts. The experiments on including implantation into rat abdominal aorta demonstrated that the obtained vascular grafts did not cause pathological reactions in the rats; in four weeks, inner side of the grafts became completely covered with endothelial cells, and fibroblasts grew throughout the wall. After exposure for 12 weeks, resorption of PLLA fibers started, and this process was completed in 64 weeks. Resorbed synthetic fibers were replaced by collagen and fibroblasts. At that time, the blood vessel was formed; its neointima and neoadventitia were close to those of the native vessel in structure and composition
Arbitrary controlled-phase gate on fluxonium qubits using differential ac-Stark shifts
Large scale quantum computing motivates the invention of two-qubit gate
schemes that not only maximize the gate fidelity but also draw minimal
resources. In the case of superconducting qubits, the weak anharmonicity of
transmons imposes profound constraints on the gate design, leading to increased
complexity of devices and control protocols. Here we demonstrate a
resource-efficient control over the interaction of strongly-anharmonic
fluxonium qubits. Namely, applying an off-resonant drive to non-computational
transitions in a pair of capacitively-coupled fluxoniums induces a
-interaction due to unequal ac-Stark shifts of the computational
levels. With a continuous choice of frequency and amplitude, the drive can
either cancel the static -term or increase it by an order of
magnitude to enable a controlled-phase (CP) gate with an arbitrary programmed
phase shift. The cross-entropy benchmarking of these non-Clifford operations
yields a sub error, limited solely by incoherent processes. Our result
demonstrates the advantages of strongly-anharmonic circuits over transmons in
designing the next generation of quantum processors
Stochastic pump effect and geometric phases in dissipative and stochastic systems
The success of Berry phases in quantum mechanics stimulated the study of
similar phenomena in other areas of physics, including the theory of living
cell locomotion and motion of patterns in nonlinear media. More recently,
geometric phases have been applied to systems operating in a strongly
stochastic environment, such as molecular motors. We discuss such geometric
effects in purely classical dissipative stochastic systems and their role in
the theory of the stochastic pump effect (SPE).Comment: Review. 35 pages. J. Phys. A: Math, Theor. (in press
Andreev levels in a single-channel conductor
We calculate the subgap density of states of a disordered single-channel
normal metal connected to a superconductor at one end (NS junction) or at both
ends (SNS junction). The probability distribution of the energy of a bound
state (Andreev level) is broadened by disorder. In the SNS case the two-fold
degeneracy of the Andreev levels is removed by disorder leading to a splitting
in addition to the broadening. The distribution of the splitting is given
precisely by Wigner's surmise from random-matrix theory. For strong disorder
the mean density of states is largely unaffected by the proximity to the
superconductor, because of localization, except in a narrow energy region near
the Fermi level, where the density of states is suppressed with a log-normal
tail.Comment: 12 pages, 5 figure
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