7,725 research outputs found
A Quantum-Proof Non-Malleable Extractor, With Application to Privacy Amplification against Active Quantum Adversaries
In privacy amplification, two mutually trusted parties aim to amplify the
secrecy of an initial shared secret in order to establish a shared private
key by exchanging messages over an insecure communication channel. If the
channel is authenticated the task can be solved in a single round of
communication using a strong randomness extractor; choosing a quantum-proof
extractor allows one to establish security against quantum adversaries.
In the case that the channel is not authenticated, Dodis and Wichs (STOC'09)
showed that the problem can be solved in two rounds of communication using a
non-malleable extractor, a stronger pseudo-random construction than a strong
extractor.
We give the first construction of a non-malleable extractor that is secure
against quantum adversaries. The extractor is based on a construction by Li
(FOCS'12), and is able to extract from source of min-entropy rates larger than
. Combining this construction with a quantum-proof variant of the
reduction of Dodis and Wichs, shown by Cohen and Vidick (unpublished), we
obtain the first privacy amplification protocol secure against active quantum
adversaries
Uncomputably noisy ergodic limits
V'yugin has shown that there are a computable shift-invariant measure on
Cantor space and a simple function f such that there is no computable bound on
the rate of convergence of the ergodic averages A_n f. Here it is shown that in
fact one can construct an example with the property that there is no computable
bound on the complexity of the limit; that is, there is no computable bound on
how complex a simple function needs to be to approximate the limit to within a
given epsilon
Isotopic dependence of the giant monopole resonance in the even-A ^{112-124}Sn isotopes and the asymmetry term in nuclear incompressibility
The strength distributions of the giant monopole resonance (GMR) have been
measured in the even-A Sn isotopes (A=112--124) with inelastic scattering of
400-MeV particles in the angular range
--. We find that the experimentally-observed GMR energies
of the Sn isotopes are lower than the values predicted by theoretical
calculations that reproduce the GMR energies in Pb and Zr very
well. From the GMR data, a value of MeV is obtained
for the asymmetry-term in the nuclear incompressibility.Comment: Submitted to Physical Review Letters. 10 pages; 4 figure
Proton decay from the isoscalar giant dipole resonance in Ni
Proton decay from the 3 isoscalar giant dipole resonance (ISGDR)
in Ni has been measured using the () reaction at a
bombarding energy of 386 MeV to investigate its decay properties. We have
extracted the ISGDR strength under the coincidence condition between
inelastically scattered particles at forward angles and decay protons
emitted at backward angles. Branching ratios for proton decay to low-lying
states of Co have been determined, and the results compared to
predictions of recent continuum-RPA calculations. The final-state spectra of
protons decaying to the low-lying states in Co were analyzed for a more
detailed understanding of the structure of the ISGDR. It is found that there
are differences in the structure of the ISGDR as a function of excitation
energy.Comment: Minor changes after review. Accepted for publication in Phys. Rev. C.
19 pages; 7 figure
Evidence for particle-hole excitations in the triaxial strongly-deformed well of ^{163}Tm
Two interacting, strongly-deformed triaxial (TSD) bands have been identified
in the Z = 69 nucleus ^{163}Tm. This is the first time that interacting TSD
bands have been observed in an element other than the Z = 71 Lu nuclei, where
wobbling bands have been previously identified. The observed TSD bands in
^{163}Tm appear to be associated with particle-hole excitations, rather than
wobbling. Tilted-Axis Cranking (TAC) calculations reproduce all experimental
observables of these bands reasonably well and also provide an explanation for
the presence of wobbling bands in the Lu nuclei, and their absence in the Tm
isotopes.Comment: 13 pages, 7 figure
Nontrivial behavior of the Fermi arc in the staggered-flux ordered phase
The doping and temperature dependences of the Fermi arc in the
staggered-flux, or the d-density wave, ordered phase of the t-J model are
analyzed by the U(1) slave boson theory. Nontrivial behavior is revealed by the
self-consistent calculation. At low doped and finite-temperature region, both
the length of the Fermi arc and the width of the Fermi pocket are proportional
to and the area of the Fermi pocket is proportional to .
This behavior is completely different from that at the zero temperature, where
the area of the Fermi pocket becomes . This behavior should be
observed by detailed experiments of angle-resolved photoemission spectroscopy
in the pseudogap phase of high-T_c cuprates if the pseudogap phase is the
staggered-flux ordered phase.Comment: 4 pages, 4 figure
D-branes in PP-Waves and Massive Theories on Worldsheet with Boundary
We investigate the supersymmetric D-brane configurations in the pp-wave
backgrounds proposed by Maldacena and Maoz. We study the surviving
supersymmetry in a D-brane configuration from the worldvolume point of view.
When we restrict ourselves to the background with N=(2,2) supersymmetry and no
holomorphic Killing vector term, there are two types of supersymmetric
D-branes: A-type and B-type. An A-type brane is wrapped on a special Lagrangian
submanifold, and the imaginary part of the superpotential should be constant on
its worldvolume. On the other hand, a B-type brane is wrapped on a complex
submanifold, and the superpotential should be constant on its worldvolume. The
results are almost consistent with the worldsheet theory in the lightcone
gauge. The inclusion of gauge fields is also discussed and found BPS D-branes
with the gauge field excitations. Furthermore, we consider the backgrounds with
holomorphic Killing vector terms and N=(1,1) supersymmetric backgrounds.Comment: 27 pages, LaTeX, no figure. v2: typos corrected, comments added,
references added. v3: typos corrected, comments added, references added.
v4:typos correcte
Diamagnetic Persistent Currents and Spontaneous Time-Reversal Symmetry Breaking in Mesoscopic Structures
Recently, new strongly interacting phases have been uncovered in mesoscopic
systems with chaotic scattering at the boundaries by two of the present authors
and R. Shankar. This analysis is reliable when the dimensionless conductance of
the system is large, and is nonperturbative in both disorder and interactions.
The new phases are the mesoscopic analogue of spontaneous distortions of the
Fermi surface induced by interactions in bulk systems and can occur in any
Fermi liquid channel with angular momentum . Here we show that the phase
with even has a diamagnetic persistent current (seen experimentally but
mysterious theoretically), while that with odd can be driven through a
transition which spontaneously breaks time-reversal symmetry by increasing the
coupling to dissipative leads.Comment: 4 pages, three eps figure
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