883 research outputs found
Coherent dynamics in long fluxonium qubits
We analyze the coherent dynamics of a fluxonium device (Manucharyan et al
2009 Science 326 113) formed by a superconducting ring of Josephson junctions
in which strong quantum phase fluctuations are localized exclusively on a
single weak element. In such a system, quantum phase tunnelling by
occurring at the weak element couples the states of the ring with supercurrents
circulating in opposite directions, while the rest of the ring provides an
intrinsic electromagnetic environment of the qubit. Taking into account the
capacitive coupling between nearest neighbors and the capacitance to the
ground, we show that the homogeneous part of the ring can sustain
electrodynamic modes which couple to the two levels of the flux qubit. In
particular, when the number of Josephson junctions is increased, several
low-energy modes can have frequencies lower than the qubit frequency. This
gives rise to a quasiperiodic dynamics, which manifests itself as a decay of
oscillations between the two counterpropagating current states at short times,
followed by oscillation-like revivals at later times. We analyze how the system
approaches such a dynamics as the ring's length is increased and discuss
possible experimental implications of this non-adiabatic regime.Comment: 20 pages, 8 figures (new, substantially revised version
Ghost Kinetic Operator of Vacuum String Field Theory
Using the data of eigenvalues and eigenvectors of Neumann matrices in the
3-string vertex, we prove analytically that the ghost kinetic operator of
vacuum string field theory obtained by Hata and Kawano is equal to the ghost
operator inserted at the open string midpoint. We also comment on the values of
determinants appearing in the norm of sliver state.Comment: 19 pages, 1 figure, lanlmac; v2: typos correcte
Siegel Gauge in Vacuum String Field Theory
We study the star algebra of ghost sector in vacuum string field theory
(VSFT). We show that the star product of two states in the Siegel gauge is BRST
exact if we take the BRST charge to be the one found in hep-th/0108150, and the
BRST exact states are nil factors in the star algebra. By introducing a new
star product defined on the states in the Siegel gauge, the equation of motion
of VSFT is characterized as the projection condition with respect to this new
product. We also comment on the comma form of string vertex in the ghost
sector.Comment: 13 pages, lanlmac; v3: comment adde
Finite size Berezinski-Kosterlitz-Thouless transition at grain boundaries in solid He and role of He impurities
We analyze the complex phenomenology of the Non-Classical Rotational Inertia
(NCRI) observed at low temperature in solid He within the context of a two
dimensional Berezinski-Kosterlitz-Thouless transition in a premelted He
film at the grain boundaries. We show that both the temperature and He
doping dependence of the NCRI fraction (NCRIF) can be ascribed to finite size
effects induced by the finite grain size. We give an estimate of the average
size of the grains which we argue to be limited by the isotopic He
impurities and we provide a simple power-law relation between the NCRIF and the
He concentration.Comment: Final version, as appearing on prin
(1+1)-dimensional separation of variables
In this paper we explore general conditions which guarantee that the geodesic
flow on a 2-dimensional manifold with indefinite signature is locally
separable. This is equivalent to showing that a 2-dimensional natural
Hamiltonian system on the hyperbolic plane possesses a second integral of
motion which is a quadratic polynomial in the momenta associated with a
2nd-rank Killing tensor. We examine the possibility that the integral is
preserved by the Hamiltonian flow on a given energy hypersurface only (weak
integrability) and derive the additional requirement necessary to have
conservation at arbitrary values of the Hamiltonian (strong integrability).
Using null coordinates, we show that the leading-order coefficients of the
invariant are arbitrary functions of one variable in the case of weak
integrability. These functions are quadratic polynomials in the coordinates in
the case of strong integrability. We show that for -dimensional systems
there are three possible types of conformal Killing tensors, and therefore,
three distinct separability structures in contrast to the single standard
Hamilton-Jacobi type separation in the positive definite case. One of the new
separability structures is the complex/harmonic type which is characterized by
complex separation variables. The other new type is the linear/null separation
which occurs when the conformal Killing tensor has a null eigenvector.Comment: To appear on Journal of Mathematical Physic
Star Algebra Projectors
Surface states are open string field configurations which arise from Riemann
surfaces with a boundary and form a subalgebra of the star algebra. We find
that a general class of star algebra projectors arise from surface states where
the open string midpoint reaches the boundary of the surface. The projector
property of the state and the split nature of its wave-functional arise because
of a nontrivial feature of conformal maps of nearly degenerate surfaces.
Moreover, all such projectors are invariant under constant and opposite
translations of their half-strings. We show that the half-string states
associated to these projectors are themselves surface states. In addition to
the sliver, we identify other interesting projectors. These include a butterfly
state, which is the tensor product of half-string vacua, and a nothing state,
where the Riemann surface collapses.Comment: 65 pages, 23 figures, LaTe
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