7,608 research outputs found
Entangled coherent states versus entangled photon pairs for practical quantum information processing
We compare effects of decoherence and detection inefficiency on entangled
coherent states (ECSs) and entangled photon pairs (EPPs), both of which are
known to be particularly useful for quantum information processing (QIP). When
decoherence effects caused by photon losses are heavy, the ECSs outperform the
EPPs as quantum channels for teleportation both in fidelities and in success
probabilities. On the other hand, when inefficient detectors are used, the
teleportation scheme using the ECSs suffers undetected errors that result in
the degradation of fidelity, while this is not the case for the teleportation
scheme using the EPPs. Our study reveals the merits and demerits of the two
types of entangled states in realizing practical QIP under realistic
conditions.Comment: 9 pages, 6 figures, substantially revised version, to be published in
Phys. Rev.
GHZ-type and W-type entangled coherent states: generation and Bell-type inequality tests without photon counting
We study GHZ-type and W-type three-mode entangled coherent states. Both the
types of entangled coherent states violate Mermin's version of the Bell
inequality with threshold photon detection (i.e., without photon counting).
Such an experiment can be performed using linear optics elements and threshold
detectors with significant Bell violations for GHZ-type entangled coherent
states. However, to demonstrate Bell-type inequality violations for W-type
entangled coherent states, additional nonlinear interactions are needed. We
also propose an optical scheme to generate W-type entangled coherent states in
free-traveling optical fields. The required resources for the generation are a
single-photon source, a coherent state source, beam splitters, phase shifters,
photodetectors, and Kerr nonlinearities. Our scheme does not necessarily
require strong Kerr nonlinear interactions, i.e., weak nonlinearities can be
used for the generation of the W-type entangled coherent states. Furthermore,
it is also robust against inefficiencies of the single-photon source and the
photon detectors.Comment: 8 pages, 5 figures, to be published in Phys. Rev.
Target market selection model for e-commerce start-up exemplified by NewCo
For e-commerce startups (ECSs) international growth has never been more important than today. In order to venture abroad successfully, ECSs need a model which enables them to select the most attractive markets. The current status of theory and literature is rarely applicable to early stage ECSs. Therefore, this research paper provides a model for the systematic selection of new target markets. Based on existing literature as well as primary and secondary research, this thesis develops a generic target market selection model for ECSs. To verify this model, it is applied to a specific online market place called NewCo
Attaining subclassical metrology in lossy systems with entangled coherent states
Quantum mechanics allows entanglement enhanced measurements to be performed, but loss remains an obstacle in constructing realistic quantum metrology schemes. However, recent work has revealed that entangled coherent states (ECSs) have the potential to perform robust subclassical measurements [J. Joo et al., Phys. Rev. Lett. 107, 083601 (2011)]. Up to now no read-out scheme has been devised that exploits this robust nature of ECSs, but we present here an experimentally accessible method of achieving precision close to the theoretical bound, even with loss.We show substantial improvements over unentangled classical states and highly entangled NOON states for a wide range of loss values, elevating quantum metrology to a realizable technology in the near future
Thermal stability and aggregation of sulfolobus solfataricus b-glycosidase are dependent upon the N-e-methylation of specific lysyl residues: critical role of in vivo post-translational modifications.
Methylation in vivo is a post-translational modification observed in several organisms belonging to eucarya, bacteria, and archaea. Although important implications of this modification have been demonstrated in several eucaryotes, its biological role in hyperthermophilic archaea is far from being understood. The aim of this work is to clarify some effects of methylation on the properties of β-glycosidase from Sulfolobus solfataricus, by a structural comparison between the native, methylated protein and its unmethylated counterpart, recombinantly expressed in Escherichia coli. Analysis by Fourier transform infrared spectroscopy indicated similar secondary structure contents for the two forms of the protein. However, the study of temperature perturbation by Fourier transform infrared spectroscopy and turbidimetry evidenced denaturation and aggregation events more pronounced in recombinant than in native β-glycosidase. Red Nile fluorescence analysis revealed significant differences of surface hydrophobicity between the two forms of the protein. Unlike the native enzyme, which dissociated into SDS-resistant dimers upon exposure to the detergent, the recombinant enzyme partially dissociated into monomers. By electrospray mapping, the methylation sites of the native protein were identified. A computational analysis of β-glycosidase three-dimensional structure and comparisons with other proteins from S. solfataricus revealed analogies in the localization of methylation sites in terms of secondary structural elements and overall topology. These observations suggest a role for the methylation of lysyl residues, located in selected domains, in the thermal stabilization of β-glycosidase from S. solfataricu
- …