Quantum key distribution based on arbitrarily weak distillable entangled states

States with private correlations but little or no distillable entanglement were recently reported. Here, we consider the secure distribution of such states, i.e., the situation when an adversary gives two parties such states and they have to verify privacy. We present a protocol which enables the parties to extract from such untrusted states an arbitrarily long and secure key, even though the amount of distillable entanglement of the untrusted states can be arbitrarily small.     

Information Theories with Adversaries,Intrinsic Information,and Entanglement

There are aspects of privacy theory that are analogous to quantum theory. In particular one can define distillable key and key cost in parallel to distillable entanglement and entanglement cost. We present here classical privacy theory as a particular case of information theory with adversaries, where similar general laws hold as in entanglement theory. We place the result of Renner and Wolf—that intrinsic information is lower bound for key cost—into this general formalism. Then we show that the question of whether intrinsic information is equal to key cost is equivalent to the question of whether Alice and Bob can create a distribution product with Eve using I_M bits of secret key. We also propose a natural analogue of relative entropy of entanglement in privacy theory and show that it is equal to the intrinsic information. We also provide a formula analogous to the entanglement of formation for classical distributions. It is our pleasure to dedicate this paper to Asher Peres on the occasion of his seventieth birthday.     

BRDF reference standards for the infrared

A comparison between various recommended reference standards of diffuse reflectance in the IR is presented. It is shown that at a wavelength of 10.6 μm sulfur is the most Lambertian of the tested samples, although its powdery consistence makes it less suitable for use as a standard. Flame sprayed aluminum, with or without gold coating, also approaches a Lambertian surface and is suitable for use as a standard for BRDF measurements at 10.6 μm. Results for the BRDF of sulfur, gold-coated sandpaper, a commercial diffuse gold surface (by Labsphere) and flame sprayed aluminum are presented.     

RNA encapsidation by SV40-derived nanoparticles follows a rapid two-state mechanism

Remarkably, uniform virus-like particles self-assemble in a process that appears to follow a rapid kinetic mechanism. The mechanisms by which spherical viruses assemble from hundreds of capsid proteins around nucleic acid, however, are yet unresolved. Using time-resolved small-angle X-ray scattering (TR-SAXS), we have been able to directly visualize SV40 VP1 pentamers encapsidating short RNA molecules (500mers). This assembly process yields T = 1 icosahedral particles comprised of 12 pentamers and one RNA molecule. The reaction is nearly one-third complete within 35 ms, following a two-state kinetic process with no detectable intermediates. Theoretical analysis of kinetics, using a master equation, shows that the assembly process nucleates at the RNA and continues by a cascade of elongation reactions in which one VP1 pentamer is added at a time, with a rate of approximately 10(9) M(-1) s(-1). The reaction is highly robust and faster than the predicted diffusion limit. The emerging molecular mechanism, which appears to be general to viruses that assemble around nucleic acids, implicates long-ranged electrostatic interactions. The model proposes that the growing nucleo-protein complex acts as an electrostatic antenna that attracts other capsid subunits for the encapsidation process.     

Solid-state density functional theory investigation of the terahertz spectra of the structural isomers 1,2-dicyanobenzene and 1,3-dicyanobenzene

The high-resolution waveguide terahertz (THz) time-domain spectra (20-100 cm(-1)) of the two structural isomers 1,2-dicyanobenzene (1,2-DCB) and 1,3-dicyanobenzene (1,3-DCB) have been modeled and assigned using solid-state density functional theory. The THz spectra of these similar molecules are distinctly different in the low-frequency region with the differences being driven by modifications of the crystal packing arrangement between the isomers. Simulations utilizing the hybrid density functionals B3LYP and PBE0 were performed to determine the origins of the observed vibrational features. External lattice vibrations (hindered translations and rotations) are found to dominate these spectra, reinforcing the need for proper solid-state models in the analysis of the THz spectra of organic molecular solids. These calculations were able to account for all of the observed spectral features exhibited by both isomers, even in the case of 1,2-DCB, where the spectrum was found to be the result of two coexisting crystalline polymorphs.     

Long Memory with Seasonal Effects

This review is devoted to stationary discrete time second order processes whose covariance asymptotically behaves like an hyperbolically damped oscillating sequence. We present the two main ways of generating parametric models of this type. Then we gather some results concerning the influence of seasonality on the classical limit theorems. Finally, we present a simulation method which we use to try a semi parametric estimation procedure adapted from the non seasonal situation.     

Locking entanglement with a single qubit

We study the loss of entanglement of a bipartite state subjected to discarding or measurement of one qubit. Examining behavior of different entanglement measures, we find that entanglement of formation, entanglement cost, logarithmic negativity, and one-way distillable entanglement are lockable measures in that they can decrease arbitrarily after measuring one qubit. We prove that any convex and asymptotically noncontinuous measure is lockable. As a consequence, all the convex-roof measures can be locked. The relative entropy of entanglement is shown to be a nonlockable measure.