29,933 research outputs found
Increasing and decreasing entanglement characteristics for continuous variables by a local photon subtraction
We investigate how the entanglement characteristics of a non-Gaussian
entangled state are increased or decreased by a local photon subtraction
operation. The non-Gaussian entangled state is generated by injecting a
single-mode non-Gaussian state and a vacuum state into a 50:50 beam splitter.
We consider a photon-added coherent state and an odd coherent state as a
single-mode non-Gaussian state. In the regime of small amplitude, we show that
the performance of quantum teleportation and the second-order
Einstein-Podolsky- Rosen-type correlation can both be enhanced, whereas the
degree of entanglement decreases, for the output state when a local photon
subtraction operation is applied to the non-Gaussian entangled state. The
counterintuitive effect is more prominent in the limit of nearly zero
amplitude.Comment: Published version, 7 pages, 3 figure
Estimation of COVID-19 spread curves integrating global data and borrowing information
Currently, novel coronavirus disease 2019 (COVID-19) is a big threat to
global health. The rapid spread of the virus has created pandemic, and
countries all over the world are struggling with a surge in COVID-19 infected
cases. There are no drugs or other therapeutics approved by the US Food and
Drug Administration to prevent or treat COVID-19: information on the disease is
very limited and scattered even if it exists. This motivates the use of data
integration, combining data from diverse sources and eliciting useful
information with a unified view of them. In this paper, we propose a Bayesian
hierarchical model that integrates global data for real-time prediction of
infection trajectory for multiple countries. Because the proposed model takes
advantage of borrowing information across multiple countries, it outperforms an
existing individual country-based model. As fully Bayesian way has been
adopted, the model provides a powerful predictive tool endowed with uncertainty
quantification. Additionally, a joint variable selection technique has been
integrated into the proposed modeling scheme, which aimed to identify possible
country-level risk factors for severe disease due to COVID-19
Gaussian benchmark for optical communication aiming towards ultimate capacity
We establish the fundamental limit of communication capacity within Gaussian
schemes under phase-insensitive Gaussian channels, which employ multimode
Gaussian states for encoding and collective Gaussian operations and
measurements for decoding. We prove that this Gaussian capacity is additive,
i.e., its upper bound occurs with separable encoding and separable receivers so
that a single-mode communication suffices to achieve the largest capacity under
Gaussian schemes. This rigorously characterizes the gap between the ultimate
Holevo capacity and the capacity within Gaussian communication, showing that
Gaussian regime is not sufficient to achieve the Holevo bound particularly in
the low-photon regime. Furthermore the Gaussian benchmark established here can
be used to critically assess the performance of non-Gaussian protocols for
optical communication. We move on to identify non-Gaussian schemes to beat the
Gaussian capacity and show that a non-Gaussian receiver recently implemented by
Becerra et al. [Nat. Photon. 7, 147 (2013)] can achieve this aim with an
appropriately chosen encoding strategy.Comment: 9 pages, 6 figures, with supplemental materia
Continuous-variable dense coding via a general Gaussian state: Monogamy relation
We study a continuous variable (CV) dense-coding protocol, originally
proposed to employ a two-mode squeezed state, using a general two-mode Gaussian
state as a quantum channel. We particularly obtain conditions to manifest
quantum advantage by beating two well-known single-mode schemes, namely, the
squeezed-state scheme (best Gaussian scheme) and the number-state scheme
(optimal scheme achieving the Holevo bound). We then extend our study to a
multipartite Gaussian state and investigate the monogamy of operational
entanglement measured by the communication capacity under the dense-coding
protocol. We show that this operational entanglement represents a strict
monogamy relation, by means of Heisenberg's uncertainty principle among
different parties, i.e., the quantum advantage for communication can be
possible for only one pair of two-mode systems among many parties
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