2,495 research outputs found
On the energy-shell contributions of the three-particle~-~ three-hole excitations
The response functions for the extended second and third random phase
approximation are compared. A second order perturbation calculation shows that
the first-order amplitude for the direct excitation from the ground
state cancels with those that are engendered by the - coupling. As
a consequence nonvanishing effects to the response involve off
energy shell renormalization only. On shell processes are absent.Comment: 12 pages text (LaTex) and 1 figure included, to be published in Phys.
Rev.
Comment on ``Local dimer-adatom stacking fault structures from 3x3 to 13x13 along Si(111)-7x7 domain boundaries''
Zhao et al. [Phys.Rev.B 58, 13824 (1998)] depicted several atomic structures
of domain boundaries on a Si(111) surface and criticized the article by the
present author and the co-workers. I will point out that their criticism is
incorrect and their structure models have no consistency.Comment: 2 pages. Physical Review B, to appea
Boundary States for Supertubes in Flat Spacetime and Godel Universe
We construct boundary states for supertubes in the flat spacetime. The T-dual
objects of supertubes are moving spiral D1-branes (D-helices). Since we can
obtain these D-helices from the usual D1-branes via null deformation, we can
construct the boundary states for these moving D-helices in the covariant
formalism. Using these boundary states, we calculate the vacuum amplitude
between two supertubes in the closed string channel and read the open string
spectrum via the open closed duality. We find there are critical values of the
energy for on-shell open strings on the supertubes due to the non-trivial
stringy correction. We also consider supertubes in the type IIA Godel universe
in order to use them as probes of closed timelike curves. This universe is the
T-dual of the maximally supersymmetric type IIB PP-wave background. Since the
null deformations of D-branes are also allowed in this PP-wave, we can
construct the boundary states for supertubes in the type IIA Godel universe in
the same way. We obtain the open string spectrum on the supertube from the
vacuum amplitude between supertubes. As a consequence, we find that the
tachyonic instability of open strings on the supertube, which is the signal of
closed time like curves, disappears due to the stringy correction.Comment: 26 pages, 3 figures, v2: explanations added, references added, v3:
explanations adde
Holographic Derivation of Entanglement Entropy from AdS/CFT
A holographic derivation of the entanglement entropy in quantum (conformal)
field theories is proposed from AdS/CFT correspondence. We argue that the
entanglement entropy in d+1 dimensional conformal field theories can be
obtained from the area of d dimensional minimal surfaces in AdS_{d+2},
analogous to the Bekenstein-Hawking formula for black hole entropy. We show
that our proposal perfectly reproduces the correct entanglement entropy in 2D
CFT when applied to AdS_3. We also compare the entropy computed in AdS_5 \times
S^5 with that of the free N=4 super Yang-Mills.Comment: 5 pages, 3 figures, Revtex, references adde
A holographic proof of the strong subadditivity of entanglement entropy
When a quantum system is divided into subsystems, their entanglement
entropies are subject to an inequality known as "strong subadditivity". For a
field theory this inequality can be stated as follows: given any two regions of
space and , . Recently, a
method has been found for computing entanglement entropies in any field theory
for which there is a holographically dual gravity theory. In this note we give
a simple geometrical proof of strong subadditivity employing this holographic
prescription.Comment: 9 pages, 3 figure
Analysis of exchange terms in a projected ERPA Theory applied to the quasi-elastic (e,e') reaction
A systematic study of the influence of exchange terms in the longitudinal and
transverse nuclear response to quasi-elastic (e,e') reactions is presented. The
study is performed within the framework of the extended random phase
approximation (ERPA), which in conjuction with a projection method permits a
separation of various contributions tied to different physical processes. The
calculations are performed in nuclear matter up to second order in the residual
interaction for which we take a (pi+rho)-model with the addition of the
Landau-Migdal g'-parameter. Exchange terms are found to be important only for
the RPA-type contributions around the quasielastic peak.Comment: 29 pages, 6 figs (3 in postscript, 3 faxed on request), epsf.st
Collapse of thermal activation in moderately damped Josephson junctions
We study switching current statistics in different moderately damped
Josephson junctions: a paradoxical collapse of the thermal activation with
increasing temperature is reported and explained by interplay of two
conflicting consequences of thermal fluctuations, which can both assist in
premature escape and help in retrapping back into the stationary state. We
analyze the influence of dissipation on the thermal escape by tuning the
damping parameter with a gate voltage, magnetic field, temperature and an
in-situ capacitor.Comment: 4 pages, 4 figure
Coherent control of a flux qubit by phase-shifted resonant microwave pulses
The quantum state of a flux qubit was successfully pulse-controlled by using
a resonant microwave. We observed Ramsey fringes by applying a pair of
phase-shifted pi/2 microwave pulses without introducing detuning. With this
method, the qubit state can be rotated on an arbitrary axis in the x-y plane of
the Bloch sphere in a rotating frame. We obtained a qubit signal from a
coherent oscillation with an angular velocity of up to 2pi*11.4 Grad/s. In
combination with Rabi pulses, this method enables us to achieve full control of
single qubit operation. It also offers the possibility of orders of magnitude
increases in the speed of the arbitrary unitary gate operation.Comment: 3 pages, 3 figure
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