17,905 research outputs found
Mesoscopic multiterminal Josephson structures: I. Effects of nonlocal weak coupling
We investigate nonlocal coherent transport in ballistic four-terminal
Josephson structures (where bulk superconductors (terminals) are connected
through a clean normal layer, e.g., a two-dimensional electron gas).
Coherent anisotropic superposition of macroscopic wave functions of the
superconductors in the normal region produces phase slip lines (2D analogs to
phase slip centres) and time-reversal symmetry breaking 2D vortex states in it,
as well as such effects as phase dragging and magnetic flux transfer. The
tunneling density of local Andreev states in the normal layer was shown to
contain peaks at the positions controlled by the phase differences between the
terminals.
We have obtained general dependence of these effects on the controlling
supercurrent/phase differences between the terminals of the ballistic
mesoscopic four-terminal SQUID.Comment: 18 pages, 11 figure
Decoherence in adiabatic quantum computation
We have studied the decoherence properties of adiabatic quantum computation
(AQC) in the presence of in general non-Markovian, e.g., low-frequency, noise.
The developed description of the incoherent Landau-Zener transitions shows that
the global AQC maintains its properties even for decoherence larger than the
minimum gap at the anticrossing of the two lowest energy levels. The more
efficient local AQC, however, does not improve scaling of the computation time
with the number of qubits as in the decoherence-free case. The scaling
improvement requires phase coherence throughout the computation, limiting the
computation time and the problem size n.Comment: 4 pages, 2 figures, published versio
Quasiclassical calculation of spontaneous current in restricted geometries
Calculation of current and order parameter distribution in inhomogeneous
superconductors is often based on a self-consistent solution of Eilenberger
equations for quasiclassical Green's functions. Compared to the original Gorkov
equations, the problem is much simplified due to the fact that the values of
Green's functions at a given point are connected to the bulk ones at infinity
(boundary values) by ``dragging'' along the classical trajectories of
quasiparticles. In finite size systems, where classical trajectories undergo
multiple reflections from surfaces and interfaces, the usefulness of the
approach is no longer obvious, since there is no simple criterion to determine
what boundary value a trajectory corresponds to, and whether it reaches
infinity at all. Here, we demonstrate the modification of the approach based on
the Schophol-Maki transformation, which provides the basis for stable numerical
calculations in 2D. We apply it to two examples: generation of spontaneous
currents and magnetic moments in isolated islands of d-wave superconductor with
subdominant order-parameters s and d_{xy}, and in a grain boundary junction
between two arbitrarily oriented d-wave superconductors. Both examples are
relevant to the discussion of time-reversal symmetry breaking in unconventional
superconductors, as well as for application in quantum computing.Comment: 6 pages, Submitted for publication in the proceedings of MS+S2002
conference, Japa
Nonlocal mixing of supercurrents in Josephson ballistic point contact
We study coherent current states in the mesoscopic superconducting weak link
simultaneously subjected to the order parameter phase difference on the contact
and to the tangential to the junction interface superfluid velocity in the
banks. The Josephson current-phase relation controlled by the external
transport current is obtained. At phase difference close to pi the nonlocal
nature of the Josephson phase-dependent current results in the appearance of
two vortexlike states in the vicinity of the contact.Comment: 4 pages, 6 figures; to be published in Phys. Rev. B; e-mail:
[email protected]
Ride quality systems for commuter aircraft
The state-of-the-art in Active Ride Augmentation, specifically in terms of its feasibility for commuter aircraft applications. A literature survey was done, and the principal results are presented here through discussion of different Ride Quality Augmentation System (RQAS) designs and advances in related technologies. Recommended follow-on research areas are discussed, and a preliminary RQAS configuration for detailed design and development is proposed
Theory of pinning in a Superconducting Thin Film Pierced by a Ferromagnetic Columnar Defect
This is an analytical study of pinning and spontaneous vortex phase is a
system consisting of a superconducting thin film pierced by a long
ferromagnetic columnar defect of finite radius . The magnetic fields,
screening currents, energy and pinning forces for this system are calculated.
The interaction between the magnetic field of vortices and the magnetization
outside the plane of the film and its close proximity enhances vortex pinning
significantly. Spontaneous vortex phase appears when the magnetization of the
columnar defect is increased above a critical value. Transitions between phases
characterized by different number of flux quanta are also studied. These
results are generalized to the case when the superconductor is pierced by an
array of columnar defects.Comment: 6 pages, 4 figures, Accepted for publication in Phys. Rev.
Quantum Nondemolition Charge Measurement of a Josephson Qubit
In a qubit system, the measurement operator does not necessarily commute with
the qubit Hamiltonian, so that the readout process demolishes (mixes) the qubit
energy eigenstates. The readout time is therefore limited by such a mixing time
and its fidelity will be reduced. A quantum nondemolition readout scheme is
proposed in which the charge of a flux qubit is measured. The measurement
operator is shown to commute with the qubit Hamiltonian in the reduced
two-level Hilbert space, even though the Hamiltonian contains non-commuting
charge and flux terms.Comment: 4 pages, 3 figures, a paragraph added to describe how the scheme
works in charge regim
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