Quantum communication with photons

Mario Krenn, Mehul Malik, Thomas Scheidl, Rupert Ursin, Anton Zeilinger
The secure communication of information plays an ever increasing role in our society today. Classical methods of encryption inherently rely on the difficulty of solving a problem such as finding prime factors of large numbers and can, in principle, be cracked by a fast enough machine. The burgeoning field of quantum communication relies on the fundamental laws of physics to offer unconditional information security. Here we introduce the key concepts of quantum superposition and entanglement as well as the no-cloning theorem that form the basis of this field. Then, we review basic quantum communication schemes with single and entangled photons and discuss recent experimental progress in ground and space-based quantum communication. Finally, we discuss the emerging field of high-dimensional quantum communication, which promises increased data rates and higher levels of security than ever before. We discuss recent experiments that use the orbital angular momentum of photons for sharing large amounts of information in a secure fashion.
Read more at https://arxiv.org/pdf/1701.00989v1.pdf

Life under a black sun


(a) Projection system for interaction of a Lambertian radiator with the black hole. The arrows represent radiation from the cold surface at temperature Tc directed to the black hole. The remaining surface at temperature TH interacts by radiation (not shown) with the hot sky. (b) Scheme of the thermodynamic system: the planet covered with the light concentration systems shown in (a) accepts high-energy photons (long arrows) from space and sends low-energy photons (short arrows) to the black hole.

Life is dependent on the income of energy with low entropy and the disposal of energy with high entropy. On Earth, the low-entropy energy is provided by solar radiation and the high-entropy energy is disposed of as infrared radiation emitted into cold space. Here, we turn the situation around and imagine the cosmic background radiation as the low-entropy source of energy for a planet orbiting a black hole into which the high-entropy energy is expelled. We estimate the power that can be produced by thermodynamic processes on such a planet, with a particular interest in planets orbiting a fast rotating Kerr black hole as in the science fiction movie Interstellar. We also briefly discuss a reverse Dyson sphere absorbing cosmic background radiation from the outside and dumping waste energy to a black hole inside.
read more at http://aapt.scitation.org/doi/full/10.1119/1.4966905