89 research outputs found
Device independent quantum key distribution secure against coherent attacks with memoryless measurement devices
Device independent quantum key distribution aims to provide a higher degree
of security than traditional QKD schemes by reducing the number of assumptions
that need to be made about the physical devices used. The previous proof of
security by Pironio et al. applies only to collective attacks where the state
is identical and independent and the measurement devices operate identically
for each trial in the protocol. We extend this result to a more general class
of attacks where the state is arbitrary and the measurement devices have no
memory. We accomplish this by a reduction of arbitrary adversary strategies to
qubit strategies and a proof of security for qubit strategies based on the
previous proof by Pironio et al. and techniques adapted from Renner.Comment: 13 pages. Expanded main proofs with more detail, miscellaneous edits
for clarit
Determinism and Computational Power of Real Measurement-based Quantum Computation
International audienceMeasurement-based quantum computing (MBQC) is a universal model for quantum computation. The combinatorial characterisation of determinism in this model, powered by measurements, and hence, fundamentally probabilistic, is the cornerstone of most of the breakthrough results in this field. The most general known sufficient condition for a deterministic MBQC to be driven is that the underlying graph of the computation has a particular kind of flow called Pauli flow. The necessity of the Pauli flow was an open question. We show that the Pauli flow is necessary for real-MBQC, and not in general providing counterexamples for (complex) MBQC. We explore the consequences of this result for real MBQC and its applications. Real MBQC and more generally real quantum computing is known to be universal for quantum computing. Real MBQC has been used for interactive proofs by McKague. The two-prover case corresponds to real-MBQC on bipartite graphs. While (complex) MBQC on bipartite graphs are universal, the universality of real MBQC on bipartite graphs was an open question. We show that real bipartite MBQC is not universal proving that all measurements of real bipartite MBQC can be parallelised leading to constant depth computations. As a consequence, McKague techniques cannot lead to two-prover interactive proofs
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Orthographic facilitation in oral vocabulary acquisition
An experiment investigated whether exposure to orthography facilitates oral vocabulary learning. A total of 58 typically developing children aged 8-9 years were taught 12 nonwords. Children were trained to associate novel phonological forms with pictures of novel objects. Pictures were used as referents to represent novel word meanings. For half of the nonwords children were additionally exposed to orthography, although they were not alerted to its presence, nor were they instructed to use it. After this training phase a nonword-picture matching posttest was used to assess learning of nonword meaning, and a spelling posttest was used to assess learning of nonword orthography. Children showed robust learning for novel spelling patterns after incidental exposure to orthography. Further, we observed stronger learning for nonword-referent pairings trained with orthography. The degree of orthographic facilitation observed in posttests was related to children's reading levels, with more advanced readers showing more benefit from the presence of orthography
Rigidity of quantum steering and one-sided device-independent verifiable quantum computation
The relationship between correlations and entanglement has played a major
role in understanding quantum theory since the work of Einstein, Podolsky and
Rosen (1935). Tsirelson (1980) proved that Bell states, shared among two
parties, when measured suitably, achieve the maximum non-local correlations
allowed by quantum mechanics. Conversely, Reichardt, Unger and Vazirani (2013)
showed that observing the maximal correlation value over a sequence of repeated
measurements, implies that the underlying quantum state is close to a tensor
product of maximally entangled states and, moreover, that it is measured
according to an ideal strategy. However, this strong rigidity result comes at a
high price, requiring a large number of entangled pairs to be tested. In this
paper, we present a significant improvement in terms of the overhead by instead
considering quantum steering where the device of the one side is trusted. We
first demonstrate a robust one-sided device-independent version of
self-testing, which characterises the shared state and measurement operators of
two parties up to a certain bound. We show that this bound is optimal up to
constant factors and we generalise the results for the most general attacks.
This leads us to a rigidity theorem for maximal steering correlations. As a key
application we give a one-sided device-independent protocol for verifiable
delegated quantum computation, and compare it to other existing protocols, to
highlight the cost of trust assumptions. Finally, we show that under reasonable
assumptions, the states shared in order to run a certain type of verification
protocol must be unitarily equivalent to perfect Bell states.Comment: Journal version. We acknowledge discussions with Matty J Hoban on his
and Ivan \v{S}upi\'c's independent work on self-testing using quantum
steering, arXiv:1601.0155
Exploring concepts of health with male prisoners in three category-C English prisons
Lay understandings of health and illness have a well established track record and a plethora of research now exists which has examined these issues. However, there is a dearth of research which has examined the perspectives of those who are imprisoned. This paper attempts to address this research gap. The paper is timely given that calls have been made to examine lay perspectives in different geographical locations and a need to re-examine health promotion approaches in prison settings. Qualitative data from thirty-six male sentenced prisoners from three prisons in England were collected. The data was analysed in accordance with Attride-Stirling's (2001) thematic network approach. Although the men's perceptions of health were broadly similar to the general population, some interesting findings emerged which were directly related to prison life and its associated structures. These included access to the outdoors and time out of their prison cell, as well as maintaining relationships with family members through visits. The paper proposes that prisoners' lay views should be given higher priority given that prison health has traditionally been associated with medical treatment and the bio-medical paradigm more generally. It also suggests that in order to fulfil the World Health Organization's (WHO) vision of viewing prisons as health promoting settings, lay views should be recognised to shape future health promotion policy and practice
Verification of Quantum Computation: An Overview of Existing Approaches
International audienc
Quantum Tasks in Minkowski Space
The fundamental properties of quantum information and its applications to
computing and cryptography have been greatly illuminated by considering
information-theoretic tasks that are provably possible or impossible within
non-relativistic quantum mechanics. I describe here a general framework for
defining tasks within (special) relativistic quantum theory and illustrate it
with examples from relativistic quantum cryptography and relativistic
distributed quantum computation. The framework gives a unified description of
all tasks previously considered and also defines a large class of new questions
about the properties of quantum information in relation to Minkowski causality.
It offers a way of exploring interesting new fundamental tasks and
applications, and also highlights the scope for a more systematic understanding
of the fundamental information-theoretic properties of relativistic quantum
theory
What does security culture look like for small organizations?
The human component is a significant factor in information security, with a large numbers of breaches occurring due to unintentional user error. Technical solutions can only protect information so far and thus the human aspect of security has become a major focus for discussion. Therefore, it is important for organisations to create a security conscious culture. However, currently there is no established representation of security culture from which to assess how it can be manoeuvred to improve the overall information security of an organization. This is of particular importance for small organizations who lack the resources in information security and for whom the culture of the organization exerts a strong influence. A review of multiple definitions and descriptions of security culture was made to assess and analyse the drivers and influences that exist for security culture in small organizations. An initial representation of the factors that should drive security culture, together with those that should only influence it, was constructed. At a fundamental level these drivers are related to a formulated response to security issues rather than a reaction to it, and should reflect the responsibility allocated in a secure environment. In contrast, the influences on security culture can be grouped by communities of practice, individual awareness and organizational management. The encapsulation of potential driving and influencing factors couched in information security terms rather than behavioural science terms, will allow security researchers to investigate how a security culture can be fostered to improve information security in small organizations
Can multinational companies foster institutional change and sustainable development in emerging countries? A case study.
Emerging countries present institutional necessities that hinder their sustainable
development. In the face of this challenge, companies, and in particular multinational
companies (MNCs), can foster sustainable development through their corporate social
responsibility (CSR) initiatives. This study focuses on the role of institutional change in
transforming CSR into sustainable development in emerging countries. To this end, we
propose a view of CSR focused on its institutional determinants and outcomes from a
social and developmental perspective. By using quantitative and qualitative data, we
analyse the case of three MNCs from different industries based in Europe and operating in Mexico. The case study shows how firms can stimulate institutional change in
developing economies and contribute to their sustainable development as measured
by the sustainable development goals. Various mechanisms about how this process is
made are devised: institutional entrepreneurship, multistakeholder initiatives, interconnection of different institutional dimensions, and subsidiary entrepreneurship. The case
study highlights the interaction among MNCs, developing countries, and institutions
and how firms' sustainable actions scale up to the macro level.post-print399 K
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