2,746 research outputs found
Nonunitary quantum circuit
A quantum circuit is generalized to a nonunitary one whose constituents are
nonunitary gates operated by quantum measurement. It is shown that a specific
type of one-qubit nonunitary gates, the controlled-NOT gate, as well as all
one-qubit unitary gates constitute a universal set of gates for the nonunitary
quantum circuit, without the necessity of introducing ancilla qubits. A
reversing measurement scheme is used to improve the probability of successful
nonunitary gate operation. A quantum NAND gate and Abrams-Lloyd's nonlinear
gate are analyzed as examples. Our nonunitary circuit can be used to reduce the
qubit overhead needed to ensure fault-tolerant quantum computation.Comment: 19 pages, 6 figures; added a referenc
Bell's inequality with Dirac particles
We study Bell's inequality using the Bell states constructed from four
component Dirac spinors. Spin operator is related to the Pauli-Lubanski pseudo
vector which is relativistic invariant operator. By using Lorentz
transformation, in both Bell states and spin operator, we obtain an observer
independent Bell's inequality, so that it is maximally violated as long as it
is violated maximally in the rest frame.Comment: 7 pages. arXiv admin note: text overlap with arXiv:quant-ph/0308156
by other author
Chandra Snapshot Observations of Low-Luminosity AGNs with a Compact Radio Source
The results of Chandra snapshot observations of 11 LINERs (Low-Ionization
Nuclear Emission-line Regions), three low-luminosity Seyfert galaxies, and one
HII-LINER transition object are presented. Our sample consists of all the
objects with a flat or inverted spectrum compact radio core in the VLA survey
of 48 low-luminosity AGNs (LLAGNs) by Nagar et al. (2000). An X-ray nucleus is
detected in all galaxies except one and their X-ray luminosities are in the
range 5x10^38 to 8x10^41 erg/s. The X-ray spectra are generally steeper than
expected from thermal bremsstrahlung emission from an advection-dominated
accretion flow (ADAF). The X-ray to Halpha luminosity ratios for 11 out of 14
objects are in good agreement with the value characteristic of LLAGNs and more
luminous AGNs, and indicate that their optical emission lines are predominantly
powered by a LLAGN. For three objects, this ratio is less than expected.
Comparing with properties in other wavelengths, we find that these three
galaxies are most likely to be heavily obscured AGN. We use the ratio RX = \nu
L\nu (5 GHz)/LX, where LX is the luminosity in the 2-10 keV band, as a measure
of radio loudness. In contrast to the usual definition of radio loudness (RO =
L\nu(5 GHz)/L\nu(B)), RX can be used for heavily obscured (NH >~ 10^23 cm^-2,
AV>50 mag) nuclei. Further, with the high spatial resolution of Chandra, the
nuclear X-ray emission of LLAGNs is often easier to measure than the nuclear
optical emission. We investigate the values of RX for LLAGNs, luminous Seyfert
galaxies, quasars and radio galaxies and confirm the suggestion that a large
fraction of LLAGNs are radio loud.Comment: 15 pages, accepted for publication in Ap
Five-dimensional SYM from undeformed ABJM
We expand undeformed ABJM theory around the vacuum solution that was found in
arxiv:0909.3101. This solution can be interpreted as a circle-bundle over a
two-dimensional plane with a singularity at the origin. By imposing periodic
boundary conditions locally far away from the singularity, we obtain a local
fuzzy two-torus over which we have a circle fibration. By performing
fluctuation analysis we obtain five-dimensional SYM with the precise value on
the coupling constant that we would obtain by compactifying multiple M5 branes
on the vacuum three-manifold. In the resulting SYM theory we also find a
coupling to a background two-form.Comment: 23 page
The Ionizing Source of the Nucleus of NGC1097
We present new observations in X-ray and optical/ultraviolet of the nucleus
of NGC1097, known for the abrupt appearance of broad, double-peaked Balmer
lines in its spectrum in 1991. These new observations are used to construct the
spectral energy distribution (SED) of the central engine. From the SED we infer
that this AGN is radio-loud and has a bolometric luminosity L_Bol ~ 10^42
erg/s, implying a low Eddington ratio of L_Bol/L_Edd ~ 10^{-4}. These results
suggest that the central ionizing source is an advection-dominated accretion
flow (ADAF) in the form of an ellevated structure which photoionizes an outer
thin disk. We fit a simplified ADAF model to the SED and obtain limits on the
values of the mass accretion rate Mdot and accretion efficiency \eta, namely
Mdot/Mdot_Edd >= 10^{-3} and \eta <= 10^{-2}. We identify an energy budget
problem: if the central photoionizing source is isotropic, the covering factor
of the line-emitting portion of the thin accretion disk is ~ 6, i. e. the
central source accounts for only 20% of the energy emitted in the double-peaked
Balmer lines.Comment: 4 pages, 3 figures, to appear in the proceedings of "The Interplay
among Black Holes, Stars and ISM in Galactic Nuclei", IAU 222, eds. Th.
Storchi Bergmann, L.C. Ho, and H.R. Schmit
Ghost D-brane, Supersymmetry and Matrix Model
In this note we study the world volume theory of pairs of D-brane and ghost
D-brane, which is shown to have 16 linear supersymmetries and 16 nonlinear
supersymmetries. In particular we study a matrix model based on the pairs of
D(-1)-brane and ghost D(-1)-brane. Since such pairs are supposed to be
equivalent to the closed string vacuum, we expect all 32 supersymmetries should
be unbroken. We show that the world volume theory of the pairs of D-brane and
ghost D-brane has unbroken 32 supersymmetries even though a half of them are
nonlinearly realized.Comment: 12 pages, references adde
Stringy Derivation of Nahm Construction of Monopoles
We derive the Nahm construction of monopoles from exact tachyon condensation
on unstable D-branes. The Dirac operator used in the Nahm construction is
identified with the tachyon profile in our D-brane approach, and we provide
physical interpretation of the procedures Nahm gave. Crucial is the
introduction of infinite number of brane-antibranes from which arbitrary
D-brane can be constrcuted, exhibitting a unified view of various D-branes. We
explicitly show the equivalence of the D3-brane boundary state with the
monopole profile and the D1-brane boundary state with the Nahm data as
transverse scalars.Comment: 18 pages, 4 eps figures, JHEP style, comments about low energy limits
added, references adde
Topological DBI actions and nonlinear instantons
We consider Euclidean D4 and D6-branes filling the whole and
space, respectively. In both cases, with a constant background
B-field turned on for D4-branes, we propose actions which are the same as the
DBI actions up to some constant or total derivative terms. These extra terms
allow us to write the action as a square of nonlinear instanton equations. As
such, the actions can easily be supersymmetrized using the methods of
topological field theory.Comment: 9 pages, latex, added a reference, and minor modification
Noncommutativity and Tachyon Condensation
We study the fuzzy or noncommutative Dp-branes in terms of infinitely many
unstable D0-branes, from which we can construct any Dp-branes. We show that the
tachyon condensation of the unstable D0-branes induces the noncommutativity. In
the infinite tachyon condensation limit, most of the unstable D0-branes
disappear and remaining D0-branes are actually the BPS D0-branes with the
correct noncommutative coordinates. For the fuzzy S^2 case, we explicitly show
only the D0-branes corresponding to the lowest Landau level survive in the
limit. We also show that a boundary state for a Dp-brane satisfying the
Dirichlet boundary condition on a curved submanifold embedded in the flat space
is not localized on the submanifold. This implies that the Dp-brane on it is
ambiguous at the string scale and solves the problem for a spherical D2-brane
with a unit flux on the world volume which should be equivalent to one
D0-brane. We also discuss the diffeomorphism in the D0-brane picture.Comment: 30 pages, references added, minor corrections and clarifications,
version to appear in JHE
Supertubes in Matrix model and DBI action
We show the equivalence between the supertube solutions with an arbitrary
cross section in two different actions, the DBI action for the D2-brane and the
matrix model action for the D0-branes. More precisely, the equivalence between
the supertubes in the D2-brane picture and the D0-brane picture is shown in the
boundary state formalism which is valid for all order in \alpha'. This is an
application of the method using the infinitely many D0-branes and
anti-D0-branes which was used to show other equivalence relations between two
seemingly different D-brane systems, including the D-brane realization of the
ADHM construction of instanton. We also apply this method to the superfunnel
type solutions successfully.Comment: 24 pages, references added, version to appear in JHE
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