Quantum-locked key distribution at nearly the classical capacity rate

Quantum data locking is a protocol that allows for a small secret key to (un)lock an exponentially larger amount of information, hence yielding the strongest violation of the classical one-time pad encryption in the quantum setting. This violation mirrors a large gap existing between two security criteria for quantum cryptography quantified by two entropic quantities: the Holevo information and the accessible information. We show that the latter becomes a sensible security criterion if an upper bound on the coherence time of the eavesdropper's quantum memory is known. Under this condition we introduce a protocol for secret key generation through a memoryless qudit channel. For channels with enough symmetry, such as the d-dimensional erasure and depolarizing channels, this protocol allows secret key generation at an asymptotic rate as high as the classical capacity minus one bit.Comment: v2 is close to the published version and contains only the key distribution protocols (4+5 pages), an extended version of the direct communication protocol is posted in arXiv:1410.4748 Comments always welcom

Space station power system

The major requirements and guidelines that affect the space station configuration and power system are explained. The evolution of the space station power system from the NASA program development-feasibility phase through the current preliminary design phase is described. Several early station concepts are described and linked to the present concept. Trade study selections of photovoltaic system technologies are described in detail. A summary of present solar dynamic and power management and distribution systems is also given

Compassed about with so great a cloud: the witnesses of Scottish episcopal acta before ca 1250

This article is the result of examining the witnesses to some 600 episcopal acta. Despite the unequal incidence of survival from one diocese to another and the difficulty of identifying those men who had no surname, it is possible to draw some conclusions from this type of evidence. Some-thing can be said about the bishops' clerks and chaplains, other members of their households and their relatives. There is evidence of considerable continuity of personnel from one episcopate to the next. Promotion, including movement to another diocese, can be traced, as can the arrival, growth in numbers and careers of magistri. Surnames allow a consider-ation of the origins of witnesses. Some light is thrown on the growth of cathedral chapters, the introduction of bishops' officials, the role of the Céli Dé, and on clerical dynasties, illegitimacy and pluralism. The Scottish Church is seen to be integrated into the wider Western Church

Semiclassical stationary states for nonlinear Schr\"odinger equations under a strong external magnetic field

We construct solutions to the nonlinear magnetic Schr\"odinger equation $$\left\{ \begin{aligned} - \varepsilon^2 \Delta_{A/\varepsilon^2} u + V u &= \lvert u\rvert^{p-2} u & &\text{in}\ \Omega,\\ u &= 0 & &\text{on}\ \partial\Omega, \end{aligned} \right.$$ in the semiclassical r\'egime with strong magnetic fields. In contrast with the well-studied mild magnetic field r\'egime, the limiting energy depends on the magnetic field allowing to recover the Lorentz force in the semi-classical limit. Our solutions concentrate around global or local minima of a limiting energy that depends on the electric potential and the magnetic field. The results cover unbounded domains, fast-decaying electric potential and unbounded electromagnetic fields. The construction is variational and is based on an asymptotic analysis of solutions to a penalized problem in the spirit of M. del Pino and P. Felmer.Comment: 23 pages, minor correction

Determinants of Total Factor Productivity in the Italian Regions

This paper investigates the determinants of TFP for Italian regions. We find strong evidence in favour of the factors commonly suggested by the theoretical literature. In particular, R&D expenditures and the number of researchers are positively related to regional TFP. Moreover, human capital is an important determinant of TFP. Finally, we find a strong difference between Northern and Southern regions, particularly regarding the effect of research activity and social capital. Our results are robust across different estimation methods.Total factor productivity, Italian regions, panel data, human capital, social capital

Quantum data hiding in the presence of noise

When classical or quantum information is broadcast to separate receivers, there exist codes that encrypt the encoded data such that the receivers cannot recover it when performing local operations and classical communication, but they can decode reliably if they bring their systems together and perform a collective measurement. This phenomenon is known as quantum data hiding and hitherto has been studied under the assumption that noise does not affect the encoded systems. With the aim of applying the quantum data hiding effect in practical scenarios, here we define the data-hiding capacity for hiding classical information using a quantum channel. Using this notion, we establish a regularized upper bound on the data hiding capacity of any quantum broadcast channel, and we prove that coherent-state encodings have a strong limitation on their data hiding rates. We then prove a lower bound on the data hiding capacity of channels that map the maximally mixed state to the maximally mixed state (we call these channels "mictodiactic"---they can be seen as a generalization of unital channels when the input and output spaces are not necessarily isomorphic) and argue how to extend this bound to generic channels and to more than two receivers.Comment: 12 pages, accepted for publication in IEEE Transactions on Information Theor