12,297 research outputs found
Transition from antibunching to bunching in cavity QED
The photon statistics of the light emitted from an atomic ensemble into a
single field mode of an optical cavity is investigated as a function of the
number of atoms. The light is produced in a Raman transition driven by a pump
laser and the cavity vacuum [M.Hennrich et al., Phys. Rev. Lett. 85, 4672
(2000)], and a recycling laser is employed to repeat this process continuously.
For weak driving, a smooth transition from antibunching to bunching is found
for about one intra-cavity atom. Remarkably, the bunching peak develops within
the antibunching dip. For saturated driving and a growing number of atoms, the
bunching amplitude decreases and the bunching duration increases, indicating
the onset of Raman lasing.Comment: 4 pages, 4 figure
Template attacks on different devices
Template attacks remain a most powerful side-channel technique
to eavesdrop on tamper-resistant hardware. They use a profiling
step to compute the parameters of a multivariate normal distribution
from a training device and an attack step in which the parameters obtained
during profiling are used to infer some secret value (e.g. cryptographic
key) on a target device. Evaluations using the same device for
both profiling and attack can miss practical problems that appear when
using different devices. Recent studies showed that variability caused by
the use of either different devices or different acquisition campaigns on
the same device can have a strong impact on the performance of template
attacks. In this paper, we explore further the effects that lead to
this decrease of performance, using four different Atmel XMEGA 256
A3U 8-bit devices. We show that a main difference between devices is a
DC offset and we show that this appears even if we use the same device
in different acquisition campaigns. We then explore several variants of
the template attack to compensate for these differences. Our results show
that a careful choice of compression method and parameters is the key
to improving the performance of these attacks across different devices.
In particular we show how to maximise the performance of template
attacks when using Fisher's Linear Discriminant Analysis or Principal
Component Analysis. Overall, we can reduce the entropy of an unknown
8-bit value below 1.5 bits even when using different devices.Omar Choudary is a recipient of the Google Europe Fellowship in
Mobile Security, and this research is supported in part by this Google Fellowship. The
opinions expressed in this paper do not represent the views of Google unless otherwise
explicitly stated.This is the author accepted manuscript. The final version is available from Springer at http://link.springer.com/chapter/10.1007%2F978-3-319-10175-0_13
Two-dimensional vibrational spectroscopy of a double minimum system in a dissipative environment
Spiral Growth and Step Edge Barriers
The growth of spiral mounds containing a screw dislocation is compared to the
growth of wedding cakes by two-dimensional nucleation. Using phase field
simulations and homoepitaxial growth experiments on the Pt(111) surface we show
that both structures attain the same characteristic large scale shape when a
significant step edge barrier suppresses interlayer transport. The higher
vertical growth rate observed for the spiral mounds on Pt(111) reflects the
different incorporation mechanisms for atoms in the top region and can be
formally represented by an enhanced apparent step edge barrier.Comment: 11 pages, 4 figures, partly in colo
Controlled photon transfer between two individual nanoemitters via shared high-Q modes of a microsphere resonator
We realize controlled cavity-mediated photon transfer between two single
nanoparticles over a distance of several tens of micrometers. First, we show
how a single nanoscopic emitter attached to a near-field probe can be coupled
to high-Q whispering-gallery modes of a silica microsphere at will. Then we
demonstrate transfer of energy between this and a second nanoparticle deposited
on the sphere surface. We estimate the photon transfer efficiency to be about
six orders of magnitude higher than that via free space propagation at
comparable separations.Comment: accepted for publication in Nano Letter
Witnessing Entanglement of EPR States With Second-Order Interference
The separability of the continuous-variable EPR state can be tested with
Hanbury-Brown and Twiss type interference. The second-order visibility of such
interference can provide an experimental test of entanglement. It is shown that
time-resolved interference leads to the Hong, Ou and Mandel deep, that provides
a signature of quantum non-separability for pure and mixed EPR states. A
Hanbury-Brown and Twiss type witness operator can be constructed to test the
quantum nature of the EPR entanglement.Comment: 9 pages, 5 figure
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