6,072 research outputs found
Entanglement-Assisted Absorption Spectroscopy
Spectroscopy is an important tool for probing the properties of materials, chemicals and biological samples. We design a practical transmitter-receiver system that exploits entanglement to achieve a provable quantum advantage over all spectroscopic schemes based on classical sources. To probe the absorption spectra, modelled as pattern of transmissivities among different frequency modes, we employ broad-band signal-idler pairs in two-mode squeezed vacuum states. At the receiver side, we apply photodetection after optical parametric amplification. Finally, we perform a maximal-likehihood decision test on the measurement results, achieving orders-of-magnitude-lower error probability than the optimum classical systems in various examples, including `wine-tasting' and `drug-testing' where real molecules are considered. In detecting the presence of an absorption line, our quantum scheme achieves the optimum performance allowed by quantum mechanics. The quantum advantage in our system is robust against noise and loss, which makes near-term experimental demonstration possible
Development of online education and its applicationin Shanghai Maritime University
Online teaching is becoming an important alternative approach to maritime education, which traditionally relies on face-to-face instruction, particularly during the period when the COVID-19 has had a devastating impact on the educational system worldwide. On the base of the conceptualization of online education through a literature review, this study demonstrates the case of an innovative online teaching system developed and implemented by Shanghai Maritime University (SMU) that successfully allowed some 20,000 students to resume learning despite the COVID-19 disruption. To realize large-scale online teaching, four phases of development the SMU underwent are introduced. The whole process of planning, preparation, implementation as well as evaluation is elaborated. In addition to class teaching, other major activities delivered remotely are also introduced, including short-term training programs, graduation ceremony, online career fairs, online interviews for postgraduate admission. Difficulties and challenges in shifting to the new teaching method and how SMU developed effective strategies to solve these issues are addressed. This study provides a valuable example of an online teaching system realized in a maritime institution. Furthermore, it may serve as an inspirational reference to peer maritime institutions to adopt or improve their competence of online learning systems
Optimal entanglement-assisted electromagnetic sensing and communication in the presence of noise
High time-bandwidth product signal and idler pulses comprised of independent
identically distributed two-mode squeezed vacuum (TMSV) states are readily
produced by spontaneous parametric downconversion. These pulses are virtually
unique among entangled states in that they offer quantum performance advantages
-- over their best classical-state competitors -- in scenarios whose loss and
noise break their initial entanglement. Broadband TMSV states' quantum
advantage derives from its signal and idler having a strongly nonclassical
phase-sensitive cross correlation, which leads to information bearing
signatures in lossy, noisy scenarios stronger than what can be obtained from
classical-state systems of the same transmitted energy. Previous broadband TMSV
receiver architectures focused on converting phase-sensitive cross correlation
into phase-insensitive cross correlation, which can be measured in second-order
interference. In general, however, these receivers fail to deliver broadband
TMSV states' full quantum advantage, even if they are implemented with ideal
equipment. This paper introduces the correlation-to-displacement receiver -- a
new architecture comprised of a correlation-to-displacement converter, a
programmable mode selector, and a coherent-state information extractor -- that
can be configured to achieve quantum optimal performance in known sensing and
communication protocols for which broadband TMSV provides quantum advantage
that is robust against entanglement-breaking loss and noise.Comment: 14+17 pages, 12+9 figures. A preliminary version of the manuscript
can be found in arXiv:2207.0660
Entanglement-assisted capacity regions and protocol designs for quantum multiple-access channels
We solve the entanglement-assisted (EA) classical capacity region of quantum
multiple-access channels with an arbitrary number of senders. As an example, we
consider the bosonic thermal-loss multiple-access channel and solve the
one-shot capacity region enabled by an entanglement source composed of
sender-receiver pairwise two-mode squeezed vacuum states. The EA capacity
region is strictly larger than the capacity region without
entanglement-assistance. With two-mode squeezed vacuum states as the source and
phase modulation as the encoding, we also design practical receiver protocols
to realize the entanglement advantages. Four practical receiver designs, based
on optical parametric amplifiers, are given and analyzed. In the parameter
region of a large noise background, the receivers can enable a simultaneous
rate advantage of 82.0% for each sender. Due to teleportation and superdense
coding, our results for EA classical communication can be directly extended to
EA quantum communication at half of the rates. Our work provides a unique and
practical network communication scenario where entanglement can be beneficial.Comment: 8+10 pages, 11 figures, accepted by npj Quantum In
Parallel finite volume simulation of the spherical shell dynamo with pseudo-vacuum magnetic boundary conditions
In this paper, we study the parallel simulation of the magnetohydrodynamic
(MHD) dynamo in a rapidly rotating spherical shell with pseudo-vacuum magnetic
boundary conditions. A second-order finite volume scheme based on a collocated
quasi-uniform cubed-sphere grid is applied to the spatial discretization of the
MHD dynamo equations. To ensure the solenoidal condition of the magnetic field,
we adopt a widely-used approach whereby a pseudo-pressure is introduced into
the induction equation. The temporal integration is split by a second-order
approximate factorization approach, resulting in two linear algebraic systems
both solved by a preconditioned Krylov subspace iterative method. A multi-level
restricted additive Schwarz preconditioner based on domain decomposition and
multigrid method is then designed to improve the efficiency and scalability.
Accurate numerical solutions of two benchmark cases are obtained with our code,
comparable to the existing local method results. Several large-scale tests
performed on the Sunway TaihuLight supercomputer show good strong and weak
scalabilities and a noticeable improvement from the multi-level preconditioner
with up to 10368 processor cores
Practical route to entanglement-assisted communication over noisy bosonic channels
Entanglement offers substantial advantages in quantum information processing,
but loss and noise hinder its applications in practical scenarios. Although it
has been well known for decades that the classical communication capacity over
lossy and noisy bosonic channels can be significantly enhanced by entanglement,
no practical encoding and decoding schemes are available to realize any
entanglement-enabled advantage. Here, we report structured encoding and
decoding schemes for such an entanglement-assisted communication scenario.
Specifically, we show that phase encoding on the entangled two-mode squeezed
vacuum state saturates the entanglement-assisted classical communication
capacity over a very noisy channel and overcomes the fundamental limit of
covert communication without entanglement assistance. We then construct
receivers for optimum hypothesis testing protocols under discrete phase
modulation and for optimum noisy phase estimation protocols under continuous
phase modulation. Our results pave the way for entanglement-assisted
communication and sensing in the radio-frequency and microwave spectral ranges.Comment: 10+6 pages, 13 figures; Close to the published versio
Consensus Graph Representation Learning for Better Grounded Image Captioning
The contemporary visual captioning models frequently hallucinate objects that
are not actually in a scene, due to the visual misclassification or
over-reliance on priors that resulting in the semantic inconsistency between
the visual information and the target lexical words. The most common way is to
encourage the captioning model to dynamically link generated object words or
phrases to appropriate regions of the image, i.e., the grounded image
captioning (GIC). However, GIC utilizes an auxiliary task (grounding objects)
that has not solved the key issue of object hallucination, i.e., the semantic
inconsistency. In this paper, we take a novel perspective on the issue above -
exploiting the semantic coherency between the visual and language modalities.
Specifically, we propose the Consensus Rraph Representation Learning framework
(CGRL) for GIC that incorporates a consensus representation into the grounded
captioning pipeline. The consensus is learned by aligning the visual graph
(e.g., scene graph) to the language graph that consider both the nodes and
edges in a graph. With the aligned consensus, the captioning model can capture
both the correct linguistic characteristics and visual relevance, and then
grounding appropriate image regions further. We validate the effectiveness of
our model, with a significant decline in object hallucination (-9% CHAIRi) on
the Flickr30k Entities dataset. Besides, our CGRL also evaluated by several
automatic metrics and human evaluation, the results indicate that the proposed
approach can simultaneously improve the performance of image captioning (+2.9
Cider) and grounding (+2.3 F1LOC).Comment: 9 pages, 5 figures, AAAI 202
Entanglement-Assisted Communication Surpassing the Ultimate Classical Capacity
Entanglement underpins a variety of quantum-enhanced communication, sensing,
and computing capabilities. Entanglement-assisted communication (EACOMM)
leverages entanglement pre-shared by communication parties to boost the rate of
classical information transmission. Pioneering theory works showed that EACOMM
can enable a communication rate well beyond the ultimate classical capacity of
optical communications, but an experimental demonstration of any EACOMM
advantage remains elusive. Here, we report the implementation of EACOMM
surpassing the classical capacity over lossy and noisy bosonic channels. We
construct a high-efficiency entanglement source and a phase-conjugate quantum
receiver to reap the benefit of pre-shared entanglement, despite entanglement
being broken by channel loss and noise. We show that EACOMM beats the
Holevo-Schumacher-Westmoreland capacity of classical communication by up to
14.6%, when both protocols are subject to the same power constraint at the
transmitter. As a practical performance benchmark, a classical communication
protocol without entanglement assistance is implemented, showing that EACOMM
can reduce the bit-error rate by up to 69% over the same bosonic channel. Our
work opens a route to provable quantum advantages in a wide range of quantum
information processing tasks.Comment: 12 pages, 5 figures. Comments are welcom
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