38 research outputs found
Self-suppressed quantum diffusion and fundamental noise limit of soliton microcombs
Quantum diffusion of soliton microcombs has long been recognized as their
fundamental noise limit. Here we surpass such limit by utilizing dispersive
wave dynamics in multimode microresonators. Through the recoil force provided
by these dispersive waves, the quantum diffusion can be suppressed to a much
lower level that forms the ultimate fundamental noise limit of soliton
microcombs. Our findings enable coherence engineering of soliton microcombs in
the quantum-limited regime, providing critical guidelines for using soliton
microcombs to synthesize ultralow-noise microwave and optical signals.Comment: 8 pages, 5 figure
Microresonator-referenced soliton microcombs with zeptosecond-level timing noise
Optical frequency division relies on optical frequency combs to coherently
translate ultra-stable optical frequency references to the microwave domain.
This technology has enabled microwave synthesis with ultralow timing noise, but
the required instruments are too bulky for real-world applications. Here, we
develop a compact optical frequency division system using microresonator-based
frequency references and comb generators. The soliton microcomb formed in an
integrated SiN microresonator is stabilized to two lasers referenced to
an ultrahigh- MgF microresonator. Photodetection of the soliton pulse
train produces 25 GHz microwaves with absolute phase noise of -141 dBc/Hz (547
zs Hz) at 10 kHz offset frequency. The synthesized microwaves are
tested as local oscillators in jammed communication channels, resulting in
improved fidelity compared with those derived from electronic oscillators. Our
work demonstrates unprecedented coherence in miniature microwave oscillators,
providing key building blocks for next-generation timekeeping, navigation, and
satellite communication systems.Comment: 8 pages, 7 figures and table
Non-orthogonal cavity modes near exceptional points in the far field
Non-orthogonal eigenstates are a fundamental feature of non-Hermitian systems
and are accompanied by the emergence of nontrivial features. However, the
platforms to explore non-Hermitian mode couplings mainly measure near-field
effects, and the far-field behaviour remain mostly unexplored. Here, we study
how a microcavity with non-Hermitian mode coupling exhibits eigenstate
non-orthogonality by investigating the spatial field and the far-field
polarization of cavity modes. The non-Hermiticity arises from asymmetric
backscattering, which is controlled by integrating two scatterers of different
size and location into a microdisk. We observe that the spatial field overlaps
of two modes increases abruptly to its maximum value, whilst different
far-field elliptical polarizations of two modes coalesce when approaching an
exceptional point. We demonstrate such features experimentally by measuring the
far-field polarization from the fabricated microdisks. Our work reveals the
non-orthogonality in the far-field degree of freedom, and the integrability of
the microdisks paves a way to integrate more non-Hermitian optical properties
into nanophotonic systems.Comment: 11pages, 4 figure
Single charge control of localized excitons in heterostructures with ferroelectric thin films and two-dimensional transition metal dichalcogenides
Single charge control of localized excitons (LXs) in two-dimensional
transition metal dichalcogenides (TMDCs) is crucial for potential applications
in quantum information processing and storage. However, traditional
electrostatic doping method with applying metallic gates onto TMDCs may cause
the inhomogeneous charge distribution, optical quench, and energy loss. Here,
by locally controlling the ferroelectric polarization of the ferroelectric thin
film BiFeO3 (BFO) with a scanning probe, we can deterministically manipulate
the doping type of monolayer WSe2 to achieve the p-type and n-type doping. This
nonvolatile approach can maintain the doping type and hold the localized
excitonic charges for a long time without applied voltage. Our work
demonstrated that ferroelectric polarization of BFO can control the charges of
LXs effectively. Neutral and charged LXs have been observed in different
ferroelectric polarization regions, confirmed by magnetic optical measurement.
Highly circular polarization degree about 90 % of the photon emission from
these quantum emitters have been achieved in high magnetic fields. Controlling
single charge of LXs in a non-volatile way shows a great potential for
deterministic photon emission with desired charge states for photonic long-term
memory.Comment: 13 pages, 5 figure
Controllable Spin-Resolved Photon Emission Enhanced by Slow-Light Mode in Photonic Crystal Waveguides on Chip
We report the slow-light enhanced spin-resolved in-plane emission from a
single quantum dot (QD) in a photonic crystal waveguide (PCW). The slow light
dispersions in PCWs are designed to match the emission wavelengths of single
QDs. The resonance between two spin states emitted from a single QD and a slow
light mode of a waveguide is investigated under a magnetic field with Faraday
configuration. Two spin states of a single QD experience different degrees of
enhancement as their emission wavelengths are shifted by combining diamagnetic
and Zeeman effects with an optical excitation power control. A circular
polarization degree up to 0.81 is achieved by changing the off-resonant
excitation power. Strongly polarized photon emission enhanced by a slow light
mode shows great potential to attain controllable spin-resolved photon sources
for integrated optical quantum networks on chip.Comment: 7 pages,5 figure
Fourier Hull Fatigue Assessment Method’s Proposing and Software Development
In this paper, based on the spectral analysis and the strain energy theory, the systematic errors of Rain-flow Counting Method have been quantitatively analyzed, from which a Fourier Counting Method is put forward. And according to this new method, software has been developed combined with sampling data of the real container ship via rigorous theoretical derivation and compact modular design, which has certain theoretical innovation significance and practical value
Knowledge Graph Augmented Network Towards Multiview Representation Learning for Aspect-based Sentiment Analysis
Aspect-based sentiment analysis (ABSA) is a fine-grained task of sentiment
analysis. To better comprehend long complicated sentences and obtain accurate
aspect-specific information, linguistic and commonsense knowledge are generally
required in this task. However, most methods employ complicated and inefficient
approaches to incorporate external knowledge, e.g., directly searching the
graph nodes. Additionally, the complementarity between external knowledge and
linguistic information has not been thoroughly studied. To this end, we propose
a knowledge graph augmented network (KGAN), which aims to effectively
incorporate external knowledge with explicitly syntactic and contextual
information. In particular, KGAN captures the sentiment feature representations
from multiple different perspectives, i.e., context-, syntax- and
knowledge-based. First, KGAN learns the contextual and syntactic
representations in parallel to fully extract the semantic features. Then, KGAN
integrates the knowledge graphs into the embedding space, based on which the
aspect-specific knowledge representations are further obtained via an attention
mechanism. Last, we propose a hierarchical fusion module to complement these
multiview representations in a local-to-global manner. Extensive experiments on
three popular ABSA benchmarks demonstrate the effectiveness and robustness of
our KGAN. Notably, with the help of the pretrained model of RoBERTa, KGAN
achieves a new record of state-of-the-art performance.Comment: Under revie