2,546 research outputs found
Fourier mode dynamics for the nonlinear Schroedinger equation in one-dimensional bounded domains
We analyze the 1D focusing nonlinear Schr\"{o}dinger equation in a finite
interval with homogeneous Dirichlet or Neumann boundary conditions. There are
two main dynamics, the collapse which is very fast and a slow cascade of
Fourier modes. For the cubic nonlinearity the calculations show no long term
energy exchange between Fourier modes as opposed to higher nonlinearities. This
slow dynamics is explained by fairly simple amplitude equations for the
resonant Fourier modes. Their solutions are well behaved so filtering high
frequencies prevents collapse. Finally these equations elucidate the unique
role of the zero mode for the Neumann boundary conditions
An experimental study on (2) modular symmetry in the quantum Hall system with a small spin-splitting
Magnetic-field-induced phase transitions were studied with a two-dimensional
electron AlGaAs/GaAs system. The temperature-driven flow diagram shows the
features of the (2) modular symmetry, which includes distorted
flowlines and shiftted critical point. The deviation of the critical
conductivities is attributed to a small but resolved spin splitting, which
reduces the symmetry in Landau quantization. [B. P. Dolan, Phys. Rev. B 62,
10278.] Universal scaling is found under the reduction of the modular symmetry.
It is also shown that the Hall conductivity could still be governed by the
scaling law when the semicircle law and the scaling on the longitudinal
conductivity are invalid. *corresponding author:[email protected]: The revised manuscript has been published in J. Phys.: Condens.
Matte
Quantum anti-Zeno effect without rotating wave approximation
In this paper, we systematically study the spontaneous decay phenomenon of a
two-level system under the influences of both its environment and continuous
measurements. In order to clarify some well-established conclusions about the
quantum Zeno effect (QZE) and the quantum anti-Zeno effect (QAZE), we do not
use the rotating wave approximation (RWA) in obtaining an effective
Hamiltonian. We examine various spectral distributions by making use of our
present approach in comparison with other approaches. It is found that with
respect to a bare excited state even without the RWA, the QAZE can still happen
for some cases, e.g., the interacting spectra of hydrogen. But for a physical
excited state, which is a renormalized dressed state of the atomic state, the
QAZE disappears and only the QZE remains. These discoveries inevitably show a
transition from the QZE to the QAZE as the measurement interval changes.Comment: 14 pages, 8 figure
Effects of Zeeman spin splitting on the modular symmetry in the quantum Hall effect
Magnetic-field-induced phase transitions in the integer quantum Hall effect
are studied under the formation of paired Landau bands arising from Zeeman spin
splitting. By investigating features of modular symmetry, we showed that
modifications to the particle-hole transformation should be considered under
the coupling between the paired Landau bands. Our study indicates that such a
transformation should be modified either when the Zeeman gap is much smaller
than the cyclotron gap, or when these two gaps are comparable.Comment: 8 pages, 4 figure
Radio2Text: Streaming Speech Recognition Using mmWave Radio Signals
Millimeter wave (mmWave) based speech recognition provides more possibility
for audio-related applications, such as conference speech transcription and
eavesdropping. However, considering the practicality in real scenarios, latency
and recognizable vocabulary size are two critical factors that cannot be
overlooked. In this paper, we propose Radio2Text, the first mmWave-based system
for streaming automatic speech recognition (ASR) with a vocabulary size
exceeding 13,000 words. Radio2Text is based on a tailored streaming Transformer
that is capable of effectively learning representations of speech-related
features, paving the way for streaming ASR with a large vocabulary. To
alleviate the deficiency of streaming networks unable to access entire future
inputs, we propose the Guidance Initialization that facilitates the transfer of
feature knowledge related to the global context from the non-streaming
Transformer to the tailored streaming Transformer through weight inheritance.
Further, we propose a cross-modal structure based on knowledge distillation
(KD), named cross-modal KD, to mitigate the negative effect of low quality
mmWave signals on recognition performance. In the cross-modal KD, the audio
streaming Transformer provides feature and response guidance that inherit
fruitful and accurate speech information to supervise the training of the
tailored radio streaming Transformer. The experimental results show that our
Radio2Text can achieve a character error rate of 5.7% and a word error rate of
9.4% for the recognition of a vocabulary consisting of over 13,000 words.Comment: Accepted by Proceedings of the ACM on Interactive, Mobile, Wearable
and Ubiquitous Technologies (ACM IMWUT/UbiComp 2023
Getting Information on Independently Prepared Quantum States -- When Are Individual Measurements as Powerful as Joint Measurements?
Given a composite quantum system in which the states of the subsystems are
independently (but not necessarily identically) prepared, we construct separate
measurements on the subsystems from any given joint measurement such that the
former always give at least as large information as the latter. This
construction offers new insights into the understanding of measurements on this
type of composite systems. Moreover, this construction essentially proves the
intuition that separate measurements on the subsystems are sufficient to
extract the maximal information about the separately prepared subsystems, thus
making a joint measurement unnecessary. Furthermore, our result implies that
individual attacks are as powerful as collective attacks in obtaining
information on the raw key in quantum key distribution.Comment: 5 pages, 1 figur
Quantum Hacking: Experimental demonstration of time-shift attack against practical quantum key distribution systems
Quantum key distribution (QKD) systems can send signals over more than 100 km
standard optical fiber and are widely believed to be secure. Here, we show
experimentally for the first time a technologically feasible attack, namely the
time-shift attack, against a commercial QKD system. Our result shows that,
contrary to popular belief, an eavesdropper, Eve, has a non-negligible
probability (~4%) to break the security of the system. Eve's success is due to
the well-known detection efficiency loophole in the experimental testing of
Bell inequalities. Therefore, the detection efficiency loophole plays a key
role not only in fundamental physics, but also in technological applications
such as QKD.Comment: 5 pages, 3 figures. Substantially revised versio
Decoy state quantum key distribution with two-way classical post-processing
Decoy states have recently been proposed as a useful method for substantially
improving the performance of quantum key distribution protocols when a coherent
state source is used. Previously, data post-processing schemes based on one-way
classical communications were considered for use with decoy states. In this
paper, we develop two data post-processing schemes for the decoy-state method
using two-way classical communications. Our numerical simulation (using
parameters from a specific QKD experiment as an example) results show that our
scheme is able to extend the maximal secure distance from 142km (using only
one-way classical communications with decoy states) to 181km. The second scheme
is able to achieve a 10% greater key generation rate in the whole regime of
distances
- …