84 research outputs found
Infeasibility of constructing a special orthogonal matrix for the deterministic remote preparation of arbitrary n-qubit state
In this paper, we present a polynomial-complexity algorithm to construct a
special orthogonal matrix for the deterministic remote state preparation (DRSP)
of an arbitrary n-qubit state, and prove that if n>3, such matrices do not
exist. Firstly, the construction problem is split into two sub-problems, i.e.,
finding a solution of a semi-orthogonal matrix and generating all
semi-orthogonal matrices. Through giving the definitions and properties of the
matching operators, it is proved that the orthogonality of a special matrix is
equivalent to the cooperation of multiple matching operators, and then the
construction problem is reduced to the problem of solving an XOR linear
equation system, which reduces the construction complexity from exponential to
polynomial level. Having proved that each semi-orthogonal matrix can be
simplified into a unique form, we use the proposed algorithm to confirm that
the unique form does not have any solution when n>3, which means it is
infeasible to construct such a special orthogonal matrix for the DRSP of an
arbitrary n-qubit state.Comment: 31 figure
Quantum All-Subkeys-Recovery Attacks on 6-round Feistel-2* Structure Based on Multi-Equations Quantum Claw Finding
Exploiting quantum mechanisms, quantum attacks have the potential ability to
break the cipher structure. Recently, Ito et al. proposed a quantum attack on
Feistel-2* structure (Ito et al.'s attack) based onthe Q2 model. However, it is
not realistic since the quantum oracle needs to be accessed by the adversary,
and the data complexityis high. To solve this problem, a quantum
all-subkeys-recovery (ASR) attack based on multi-equations quantum claw-finding
is proposed, which takes a more realistic model, the Q1 model, as the scenario,
and only requires 3 plain-ciphertext pairs to quickly crack the 6-round
Feistel-2* structure. First, we proposed a multi-equations quantum claw-finding
algorithm to solve the claw problem of finding multiple equations. In addition,
Grover's algorithm is used to speedup the rest subkeys recovery. Compared with
Ito et al.'s attack, the data complexity of our attack is reduced from O(2^n)
to O(1), while the time complexity and memory complexity are also significantly
reduced.Comment: 18 pages, 4 figure
All-angle zero reflection at metamaterial surfaces
The authors study theoretically reflection on the surface of a metamaterial
with a hyperbolic dispersion. It is found that reflection is strongly dependent
on how the surface is terminated with respect to the asymptote of the
hyperbolic dispersion. For a surface terminated normally to the asymptote, zero
reflection occurs for all incident angles. It is exemplified by a metamaterial
made of a periodic metal-dielectric layered structure with its surface properly
cut through numerical simulations.Comment: 3 pages, 2 figures. Appl. Phys. Lett. (in press
Source illusion devices for flexural Lamb waves using elastic metasurfaces
Metamaterials with the transformation method has greatly promoted the
development in achieving invisibility and illusion for various classical waves.
However, the requirement of tailor-made bulk materials and extreme constitutive
parameters associated to illusion designs hampers its further progress.
Inspired by recent demonstrations of metasurfaces in achieving reduced versions
of electromagnetic cloaks, we propose and experimentally demonstrate source
illusion devices to manipulate flexural waves using metasurfaces. The approach
is particularly useful for elastic waves due to the lack of form-invariance in
usual transformation methods. We demonstrate metasurfaces for shifting,
transforming and splitting a point source with "space-coiling" structures. The
effects are found to be broadband and robust against a change of source
position, with agreement from numerical simulations and Huygens-Fresnel theory.
The proposed approach provides an avenue to generically manipulate guided
elastic waves in solids, and is potentially useful for applications such as
non-destructive testing, enhanced sensing and imaging
Willis metamaterial on a structured beam
Bianisotropy is common in electromagnetics whenever a cross-coupling between
electric and magnetic responses exists. However, the analogous concept for
elastic waves in solids, termed as Willis coupling, is more challenging to
observe. It requires coupling between stress and velocity or momentum and
strain fields, which is difficult to induce in non-negligible levels, even when
using metamaterial structures. Here, we report the experimental realization of
a Willis metamaterial for flexural waves. Based on a cantilever bending
resonance, we demonstrate asymmetric reflection amplitudes and phases due to
Willis coupling. We also show that, by introducing loss in the metamaterial,
the asymmetric amplitudes can be controlled and can be used to approach an
exceptional point of the non-Hermitian system, at which unidirectional zero
reflection occurs. The present work extends conventional propagation theory in
plates and beams to include Willis coupling, and provides new avenues to tailor
flexural waves using artificial structures.Comment: 21 pages, 3 figure
Through the Lens of Core Competency: Survey on Evaluation of Large Language Models
From pre-trained language model (PLM) to large language model (LLM), the
field of natural language processing (NLP) has witnessed steep performance
gains and wide practical uses. The evaluation of a research field guides its
direction of improvement. However, LLMs are extremely hard to thoroughly
evaluate for two reasons. First of all, traditional NLP tasks become inadequate
due to the excellent performance of LLM. Secondly, existing evaluation tasks
are difficult to keep up with the wide range of applications in real-world
scenarios. To tackle these problems, existing works proposed various benchmarks
to better evaluate LLMs. To clarify the numerous evaluation tasks in both
academia and industry, we investigate multiple papers concerning LLM
evaluations. We summarize 4 core competencies of LLM, including reasoning,
knowledge, reliability, and safety. For every competency, we introduce its
definition, corresponding benchmarks, and metrics. Under this competency
architecture, similar tasks are combined to reflect corresponding ability,
while new tasks can also be easily added into the system. Finally, we give our
suggestions on the future direction of LLM's evaluation
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