367 research outputs found
High performance guided-wave asynchronous heralded single photon source
We report on a guided wave heralded photon source based on the creation of
non-degenerate photon pairs by spontaneous parametric down conversion in a
Periodically Poled Lithium Niobate waveguide. Using the signal photon at 1310
nm as a trigger, a gated detection process permits announcing the arrival of
single photons at 1550 nm at the output of a single mode optical fiber with a
high probability of 0.38. At the same time the multi-photon emission
probability is reduced by a factor of 10 compared to poissonian light sources.
Relying on guided wave technologies such as integrated optics and fiber optics
components, our source offers stability, compactness and efficiency and can
serve as a paradigm for guided wave devices applied to quantum communication
and computation using existing telecom networks
Using markers for digital engagement and social change: Tracking meaningful narrative exchange in transmedia edutainment with text analytics techniques
While social media offer an unprecedented opportunity for orchestrating large-scale communication campaigns, it is often difficult to track audience responses on various digital platforms over time and to ascertain if their engagement is aligned with the original intention. In this article, we share a promising solution—the purposive embedding and tracking of unique content elements as “markers” using text analytics techniques. Four markers were introduced in an Indian melodramatic television serial, Main Kuch Bhi Kar Sakti Hoon (I, A Woman, Can Achieve Anything), which was part of a larger transmedia edutainment initiative in India to promote sanitation, family planning, and gender equality. These markers served as anchors for audience engagement with the originally intended messaging embedded in the narratives as well as for program monitoring and evaluation. We applied various web-based tools to systematically track marker-related engagement on Facebook, Twitter, and YouTube across eight months. We also conducted semantic network analysis to better understand how marker-related social media comments evolved over time. Our investigation of using markers for digital engagement and narrative exchange in MKBKSH makes an important and timely methodological contribution to the scholarship and praxis of social and behavior change communication.Using markers for digital engagement and social change: Tracking meaningful narrative exchange in transmedia edutainment with text analytics techniquespublishedVersio
MinD-dependent conformational changes in MinE required for the Min oscillator to spatially regulate cytokinesis
MinD recruits MinE to the membrane leading to a coupled oscillation required for spatial regulation of the cytokinetic Z ring in E. coli. How these proteins interact, however, is not clear since the MinD binding regions of MinE are sequestered within a 6-stranded β-sheet and masked by N-terminal helices. Here, minE mutations are isolated that restore interaction to some MinD and MinE mutants. These mutations alter the MinE structure releasing the MinD binding regions and N-terminal helices that bind MinD and the membrane, respectively. Crystallization of MinD-MinE complexes reveals a 4-stranded β-sheet MinE dimer with the released β strands (MinD binding regions) converted to α-helices bound to MinD dimers. These results suggest a 6 stranded, β-sheet dimer of MinE ‘senses’ MinD and switches to a 4-stranded β-sheet dimer that binds MinD and contributes to membrane binding. Also, the results indicate how MinE persists at the MinD-membrane surface
MinD-dependent conformational changes in MinE required for the Min oscillator to spatially regulate cytokinesis
MinD recruits MinE to the membrane leading to a coupled oscillation required for spatial regulation of the cytokinetic Z ring in E. coli. How these proteins interact, however, is not clear since the MinD binding regions of MinE are sequestered within a 6-stranded β-sheet and masked by N-terminal helices. Here, minE mutations are isolated that restore interaction to some MinD and MinE mutants. These mutations alter the MinE structure releasing the MinD binding regions and N-terminal helices that bind MinD and the membrane, respectively. Crystallization of MinD-MinE complexes reveals a 4-stranded β-sheet MinE dimer with the released β strands (MinD binding regions) converted to α-helices bound to MinD dimers. These results suggest a 6 stranded, β-sheet dimer of MinE ‘senses’ MinD and switches to a 4-stranded β-sheet dimer that binds MinD and contributes to membrane binding. Also, the results indicate how MinE persists at the MinD-membrane surface
Entangled state quantum cryptography: Eavesdropping on the Ekert protocol
Using polarization-entangled photons from spontaneous parametric
downconversion, we have implemented Ekert's quantum cryptography protocol. The
near-perfect correlations of the photons allow the sharing of a secret key
between two parties. The presence of an eavesdropper is continually checked by
measuring Bell's inequalities. We investigated several possible eavesdropper
strategies, including pseudo-quantum non-demolition measurements. In all cases,
the eavesdropper's presence was readily apparent. We discuss a procedure to
increase her detectability.Comment: 4 pages, 2 encapsulated postscript files, PRL (tentatively) accepte
Low Cost and Compact Quantum Cryptography
We present the design of a novel free-space quantum cryptography system,
complete with purpose-built software, that can operate in daylight conditions.
The transmitter and receiver modules are built using inexpensive off-the-shelf
components. Both modules are compact allowing the generation of renewed shared
secrets on demand over a short range of a few metres. An analysis of the
software is shown as well as results of error rates and therefore shared secret
yields at varying background light levels. As the system is designed to
eventually work in short-range consumer applications, we also present a use
scenario where the consumer can regularly 'top up' a store of secrets for use
in a variety of one-time-pad and authentication protocols.Comment: 18 pages, 9 figures, to be published in New Journal of Physic
Quantum relays and noise suppression using linear optics
Probabilistic quantum non-demolition (QND) measurements can be performed
using linear optics and post-selection. Here we show how QND devices of this
kind can be used in a straightforward way to implement a quantum relay, which
is capable of extending the range of a quantum cryptography system by
suppressing the effects of detector noise. Unlike a quantum repeater, a quantum
relay system does not require entanglement purification or the ability to store
photons.Comment: minor changes; references adde
Proposal to produce long-lived mesoscopic superpositions through an atom-driven field interaction
We present a proposal for the production of longer-lived mesoscopic
superpositions which relies on two requirements: parametric amplification and
squeezed vacuum reservoir for cavity-field states. Our proposal involves the
interaction of a two-level atom with a cavity field which is simultaneously
subjected to amplification processes.Comment: 12 pages, title changed, text improved and refences adde
Probabilistic Quantum Logic Operations Using Polarizing Beam Splitters
It has previously been shown that probabilistic quantum logic operations can
be performed using linear optical elements, additional photons (ancilla), and
post-selection based on the output of single-photon detectors. Here we describe
the operation of several quantum logic operations of an elementary nature,
including a quantum parity check and a quantum encoder, and we show how they
can be combined to implement a controlled-NOT (CNOT) gate. All of these gates
can be constructed using polarizing beam splitters that completely transmit one
state of polarization and totally reflect the orthogonal state of polarization,
which allows a simple explanation of each operation. We also describe a
polarizing beam splitter implementation of a CNOT gate that is closely
analogous to the quantum teleportation technique previously suggested by
Gottesman and Chuang [Nature 402, p.390 (1999)]. Finally, our approach has the
interesting feature that it makes practical use of a quantum-eraser technique.Comment: 9 pages, RevTex; Submitted to Phys. Rev. A; additional references
inlcude
On asymptotic continuity of functions of quantum states
A useful kind of continuity of quantum states functions in asymptotic regime
is so-called asymptotic continuity. In this paper we provide general tools for
checking if a function possesses this property. First we prove equivalence of
asymptotic continuity with so-called it robustness under admixture. This allows
us to show that relative entropy distance from a convex set including maximally
mixed state is asymptotically continuous. Subsequently, we consider it arrowing
- a way of building a new function out of a given one. The procedure originates
from constructions of intrinsic information and entanglement of formation. We
show that arrowing preserves asymptotic continuity for a class of functions
(so-called subextensive ones). The result is illustrated by means of several
examples.Comment: Minor corrections, version submitted for publicatio
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