1,147 research outputs found
High Q Cavity Induced Fluxon Bunching in Inductively Coupled Josephson Junctions
We consider fluxon dynamics in a stack of inductively coupled long Josephson
junctions connected capacitively to a common resonant cavity at one of the
boundaries. We study, through theoretical and numerical analysis, the
possibility for the cavity to induce a transition from the energetically
favored state of spatially separated shuttling fluxons in the different
junctions to a high velocity, high energy state of identical fluxon modes.Comment: 8 pages, 5 figure
Angular dependence of the radiation power of a Josephson STAR-emitter
We calculate the angular dependence of the power of stimulated terahertz
amplified radiation (STAR) emitted from a voltage applied across a stack
of intrinsic Josephson junctions. During coherent emission, we assume a
spatially uniform Josephson current density in the stack acts as a surface
electric current density antenna source, and the cavity features of the stack
are contained in a magnetic surface current density source. A superconducting
substrate acts as a perfect magnetic conductor with on its
surface. The combined results agree very well with recent experimental
observations. Existing BiSrCaCuO crystals atop perfect
electric conductors could have Josephson STAR-emitter power in excess of 5 mW,
acceptable for many device applications.Comment: 3 pages 3 figure
Convergence of Quantum Annealing with Real-Time Schrodinger Dynamics
Convergence conditions for quantum annealing are derived for optimization
problems represented by the Ising model of a general form. Quantum fluctuations
are introduced as a transverse field and/or transverse ferromagnetic
interactions, and the time evolution follows the real-time Schrodinger
equation. It is shown that the system stays arbitrarily close to the
instantaneous ground state, finally reaching the target optimal state, if the
strength of quantum fluctuations decreases sufficiently slowly, in particular
inversely proportionally to the power of time in the asymptotic region. This is
the same condition as the other implementations of quantum annealing, quantum
Monte Carlo and Green's function Monte Carlo simulations, in spite of the
essential difference in the type of dynamics. The method of analysis is an
application of the adiabatic theorem in conjunction with an estimate of a lower
bound of the energy gap based on the recently proposed idea of Somma et. al.
for the analysis of classical simulated annealing using a classical-quantum
correspondence.Comment: 6 pages, minor correction
Magnetic Field Effects near the launching region of Astrophysical Jets
One of the fundamental properties of astrophysical magnetic fields is their
ability to change topology through reconnection and in doing so, to release
magnetic energy, sometimes violently. In this work, we review recent results on
the role of magnetic reconnection and associated heating and particle
acceleration in jet/accretion disk systems, namely young stellar objects
(YSOs), microquasars, and active galactic nuclei (AGNs).Comment: 9 pages, 3 figures, invited paper for the Procs. of the Conference on
High Energy Phenomena in Relativistic Outflows II, Buenos Aires, October
2009. Submitted to International Journal of Modern Physics
Convergence theorems for quantum annealing
We prove several theorems to give sufficient conditions for convergence of
quantum annealing, which is a protocol to solve generic optimization problems
by quantum dynamics. In particular the property of strong ergodicity is proved
for the path-integral Monte Carlo implementation of quantum annealing for the
transverse Ising model under a power decay of the transverse field. This result
is to be compared with the much slower inverse-log decay of temperature in the
conventional simulated annealing. Similar results are proved for the Green's
function Monte Carlo approach. Optimization problems in continuous space of
particle configurations are also discussed.Comment: 19 page
The critical behavior of frustrated spin models with noncollinear order
We study the critical behavior of frustrated spin models with noncollinear
order, including stacked triangular antiferromagnets and helimagnets. For this
purpose we compute the field-theoretic expansions at fixed dimension to six
loops and determine their large-order behavior. For the physically relevant
cases of two and three components, we show the existence of a new stable fixed
point that corresponds to the conjectured chiral universality class. This
contradicts previous three-loop field-theoretical results but is in agreement
with experiments.Comment: 4 pages, RevTe
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