884 research outputs found
Crossover of skyrmion and helical modulations in noncentrosymmetric ferromagnets
The coupling between angular (twisting) and longitudinal modulations arising
near the ordering temperature of noncentrosymmetric ferromagnets strongly
influences the structure of skyrmion states and their evolution in an applied
magnetic field. In the precursor states of cubic helimagnets, a continuous
transformation of skyrmion lattices into the saturated state is replaced by the
first-order processes accompanied by the formation of multidomain states.
Recently the effects imposed by dominant longitudinal modulations have been
reported in bulk MnSi and FeGe. Similar phenomena can be observed in the
precursor regions of cubic helimagnet epilayers and in easy-plane chiral
ferromagnets (e.g. in the hexagonal helimagnet CrNb3S6)
A 3-Subset Meet-in-the-Middle Attack: Cryptanalysis of the Lightweight Block Cipher KTANTAN
status: publishe
Nonradiating Photonics with Resonant Dielectric Nanostructures
Nonradiating sources of energy have traditionally been studied in quantum
mechanics and astrophysics, while receiving a very little attention in the
photonics community. This situation has changed recently due to a number of
pioneering theoretical studies and remarkable experimental demonstrations of
the exotic states of light in dielectric resonant photonic structures and
metasurfaces, with the possibility to localize efficiently the electromagnetic
fields of high intensities within small volumes of matter. These recent
advances underpin novel concepts in nanophotonics, and provide a promising
pathway to overcome the problem of losses usually associated with metals and
plasmonic materials for the efficient control of the light-matter interaction
at the nanoscale. This review paper provides the general background and several
snapshots of the recent results in this young yet prominent research field,
focusing on two types of nonradiating states of light that both have been
recently at the center of many studies in all-dielectric resonant meta-optics
and metasurfaces: optical {\em anapoles} and photonic {\em bound states in the
continuum}. We discuss a brief history of these states in optics, their
underlying physics and manifestations, and also emphasize their differences and
similarities. We also review some applications of such novel photonic states in
both linear and nonlinear optics for the nanoscale field enhancement, a design
of novel dielectric structures with high- resonances, nonlinear wave mixing
and enhanced harmonic generation, as well as advanced concepts for lasing and
optical neural networks.Comment: 22 pages, 9 figures, review articl
Multipolar origin of bound states in the continuum
Metasurfaces based on resonant subwavelength photonic structures enable novel
ways of wavefront control and light focusing, underpinning a new generation of
flat-optics devices. Recently emerged all-dielectric metasurfaces exhibit
high-quality resonances underpinned by the physics of bound states in the
continuum that drives many interesting concepts in photonics. Here we suggest a
novel approach to explain the physics of bound photonic states embedded into
the radiation continuum. We study dielectric metasurfaces composed of planar
periodic arrays of Mie-resonant nanoparticles ("meta-atoms") which support both
symmetry protected and accidental bound states in the continuum and employ the
multipole decomposition approach to reveal the physical mechanism of the
formation of such nonradiating states in terms of multipolar modes generated by
isolated meta-atoms. Based on the symmetry of the vector spherical harmonics,
we identify the conditions for the existence of bound states in the continuum
originating from the symmetries of both the lattice and the unit cell. Using
this formalism we predict that metasurfaces with strongly suppressed spatial
dispersion can support the bound states in the continuum with the wavevectors
forming a line in the reciprocal space. Our results provide a new way of
designing high-quality resonant photonic systems based on the physics of bound
states in the continuum.Comment: 13 pages, 7 figures, 2 table
Exploring Energy Efficiency of Lightweight Block Ciphers
Abstract. In the last few years, the field of lightweight cryptography has seen an influx in the number of block ciphers and hash functions being proposed. One of the metrics that define a good lightweight design is the energy consumed per unit operation of the algorithm. For block ciphers, this operation is the encryption of one plaintext. By studying the energy consumption model of a CMOS gate, we arrive at the conclusion that the total energy consumed during the encryption operation of an r-round unrolled architecture of any block cipher is a quadratic function in r. We then apply our model to 9 well known lightweight block ciphers, and thereby try to predict the optimal value of r at which an r-round unrolled architecture for a cipher is likely to be most energy efficient. We also try to relate our results to some physical design parameters like the signal delay across a round and algorithmic parameters like the number of rounds taken to achieve full diffusion of a difference in the plaintext/key
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