815 research outputs found
Emergent Universe in the Braneworld Scenario
According to Padmanabhan's proposal, the difference between the surface
degrees of freedom and the bulk degrees of freedom in a region of space may
result in the acceleration of Universe expansion through the relation where and
are referred to the degrees of freedom related to the matter and energy content
inside the bulk and surface area, respectively \cite{Pad1}. In this paper, we
study the dynamical effect of the extrinsic geometrical embedding of an
arbitrary four dimensional brane in a higher dimensional bulk space and
investigate the corresponding degrees of freedom. Considering the modification
of Friedmann equations arising from a general braneworld scenario, we obtain a
correction term in Padmanabhan's relation, denoting the number of degrees of
freedom related to the extrinsic geometry of the brane embedded in higher
dimensional spacetime as where is referred to the degree of freedom related to the
extrinsic geometry of the brane while and are as
well as before. Finally, we study the validity of the first and second laws of
thermodynamics for this general braneworld scenario in the state of thermal
equilibrium and in the presence of confined matter fields to the brane with the
induced geometric matter fields.Comment: 16 pages, Major revisio
Janus: An Uncertain Cache Architecture to Cope with Side Channel Attacks
Side channel attacks are a major class of attacks to crypto-systems.
Attackers collect and analyze timing behavior, I/O data, or power consumption
in these systems to undermine their effectiveness in protecting sensitive
information. In this work, we propose a new cache architecture, called Janus,
to enable crypto-systems to introduce randomization and uncertainty in their
runtime timing behavior and power utilization profile. In the proposed cache
architecture, each data block is equipped with an on-off flag to enable/disable
the data block. The Janus architecture has two special instructions in its
instruction set to support the on-off flag. Beside the analytical evaluation of
the proposed cache architecture, we deploy it in an ARM-7 processor core to
study its feasibility and practicality. Results show a significant variation in
the timing behavior across all the benchmarks. The new secure processor
architecture has minimal hardware overhead and significant improvement in
protecting against power analysis and timing behavior attacks.Comment: 4 pages, 4 figure
Identification of Decoherence-Free Subspaces Without Quantum Process Tomography
Characterizing a quantum process is the critical first step towards applying
such a process in a quantum information protocol. Full process characterization
is known to be extremely resource-intensive, motivating the search for more
efficient ways to extract salient information about the process. An example is
the identification of "decoherence-free subspaces", in which computation or
communications may be carried out, immune to the principal sources of
decoherence in the system. Here we propose and demonstrate a protocol which
enables one to directly identify a DFS without carrying out a full
reconstruction. Our protocol offers an up-to-quadratic speedup over standard
process tomography. In this paper, we experimentally identify the DFS of a
two-qubit process with 32 measurements rather than the usual 256, characterize
the robustness and efficiency of the protocol, and discuss its extension to
higher-dimensional systems.Comment: 6 pages, 5 figure
Dilaton Cosmology, Noncommutativity and Generalized Uncertainty Principle
The effects of noncommutativity and of the existence of a minimal length on
the phase space of a dilatonic cosmological model are investigated. The
existence of a minimum length, results in the Generalized Uncertainty Principle
(GUP), which is a deformed Heisenberg algebra between the minisuperspace
variables and their momenta operators. We extend these deformed commutating
relations to the corresponding deformed Poisson algebra. For an exponential
dilaton potential, the exact classical and quantum solutions in the commutative
and noncommutative cases, and some approximate analytical solutions in the case
of GUP, are presented and compared.Comment: 16 pages, 3 figures, typos correcte
Tunneling in a Cosmological Model with Violation of Strong Energy Condition
The tunneling rate, with exact prefactor, is calculated to first order in
\hbar for a closed FRW universe filled with perfect fluid violating the strong
energy condition. The calculations are performed by applying the
dilute-instanton approximation on the corresponding Duru-Kleinert path
integral. It is shown that a closed FRW universe filled with a perfect fluid
with small violation of strong energy condition is more probable to tunnel than
the same universe with large violation of strong energy condition.Comment: 11 pages, LaTe
Adaptive quantum state tomography improves accuracy quadratically
We introduce a simple protocol for adaptive quantum state tomography, which
reduces the worst-case infidelity between the estimate and the true state from
to . It uses a single adaptation step and just one
extra measurement setting. In a linear optical qubit experiment, we demonstrate
a full order of magnitude reduction in infidelity (from to ) for
a modest number of samples ().Comment: 8 pages, 7 figure
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