Quantum superadditivity in linear optics networks: sending bits via multiple access Gaussian channels

We study classical capacity regions of quantum Gaussian multiple access channels (MAC). In classical variants of such channels, whilst some capacity superadditivity-type effects such as the so called {\it water filling effect} may be achieved, a fundamental classical additivity law can still be identified, {\it viz.} adding resources to one sender is never advantageous to other senders in sending their respective information to the receiver. Here, we show that quantum resources allows violation of this law, by providing two illustrative schemes of experimentally feasible Gaussian MACs.Comment: 4 pages, 2 figure

Nonadditivity effects in classical capacities of quantum multiple-access channels

We study classical capacities of quantum multi-access channels in geometric terms revealing breaking of additivity of Holevo-like capacity. This effect is purely quantum since, as one points out, any classical multi-access channels have their regions additive. The observed non-additivity in quantum version presented here seems to be the first effect of this type with no additional resources like side classical or quantum information (or entanglement) involved. The simplicity of quantum channels involved resembles butterfly effect in case of classical channel with two senders and two receivers.Comment: 5 pages, 5 figure

Sol-gel derived (Ba,Sr)TiO3 thin films for tunable devices

The present study is devoted to synthesis and investigation of basic properties of ferroelectric thin films. The sol-gel-type chemical solution deposition method was used for preparation of (Ba0.6Sr0.4)TiO3 (BST) thin films. The thin films were characterized in terms of their microstructure, crystalline structure, chemical composition and dielectric properties. It was found that the BST thin films adopted cubic crystallographic symmetry of the space group Pm3m, whereas the chemical composition of the thin films corresponded well with the chemical composition of the solution. Complex impedance spectroscopy was used to measure frequency-dependent dielectric properties of the thin films. Due to the high tunability and low dielectric loss, great application potential of these ferroelectric thin films was considered especially as tunable dielectric devices

Sol-gel derived (Ba,Sr)TiO3 thin films for tunable devices

The present study is devoted to synthesis and investigation of basic properties of ferroelectric thin films. The sol-gel-type chemical solution deposition method was used for preparation of (Ba0.6Sr0.4)TiO3 (BST) thin films. The thin films were characterized in terms of their microstructure, crystalline structure, chemical composition and dielectric properties. It was found that the BST thin films adopted cubic crystallographic symmetry of the space group Pm3m, whereas the chemical composition of the thin films corresponded well with the chemical composition of the solution. Complex impedance spectroscopy was used to measure frequency-dependent dielectric properties of the thin films. Due to the high tunability and low dielectric loss, great application potential of these ferroelectric thin films was considered especially as tunable dielectric devices

Quantum internet using code division multiple access

A crucial open problem in large-scale quantum networks is how to efficiently transmit quantum data among many pairs of users via a common data-transmission medium. We propose a solution by developing a quantum code division multiple access (q-CDMA) approach in which quantum information is chaotically encoded to spread its spectral content, and then decoded via chaos synchronization to separate different sender-receiver pairs. In comparison to other existing approaches, such as frequency division multiple access (FDMA), the proposed q-CDMA can greatly increase the information rates per channel used, especially for very noisy quantum channels.Comment: 29 pages, 6 figure

Influence of Sn and Pb ions substitutions on dielectric properties of barium titanate

The results of the microstructural and dielectric measurements of (Ba1-xPbx)(Ti1-xSnx)O3 (BPTSx) (x = 0, 0.05, 0.10, 0.30) polycrystalline samples are presented. The samples were obtained by means of a high temperature synthesis and their expected stoichiometry was confirmed by energy dispersive spectroscopy (EDS) measurements. The dielectric properties of BPTSx were studied with the use of broadband dielectric spectroscopy. The measurements over a wide range of temperature (from 140 K to 600 K) and frequency (from 0.1 Hz to 10 MHz) were performed. The experimental results indicate an influence of Pb ions in a sublattice A and Sn ions in a sublattice B substitution on paraelectric - ferroelectric phase transition parameters. Diffused phase transitions from a paraelectric to ferroelectric state (for x = 0.10 and x = 0.30) were observed. From the electric modulus measurements in the frequency domain the relaxation times and the activation energy were determined

Structure and magnetic properties of Bi5Ti3FeO15 ceramics prepared by sintering, mechanical activation and EDAMM process. A comparative study

Three different methods were used to obtain Bi5Ti3FeO15 ceramics, i.e. solid-state sintering, mechanical activation (MA) with subsequent thermal treatment, and electrical discharge assisted mechanical milling (EDAMM). The structure and magnetic properties of produced Bi5Ti3FeO15 samples were characterized using X-ray diffraction and Mössbauer spectroscopy. The purest Bi5Ti3FeO15 ceramics was obtained by standard solid-state sintering method. Mechanical milling methods are attractive because the Bi5Ti3FeO15 compound may be formed at lower temperature or without subsequent thermal treatment. In the case of EDAMM process also the time of processing is significantly shorter in comparison with solid-state sintering method. As revealed by Mössbauer spectroscopy, at room temperature the Bi5Ti3FeO15 ceramics produced by various methods is in paramagnetic state

X-Ray diffraction, mossbauer spectroscopy, and magnetoelectric effect studies of multiferroic Bi5Ti3FeO15 ceramics

Bi5Ti3FeO15 ceramics belongs to multiferroic class of materials. In this work it was prepared by solidstate sintering method and investigated by X-ray di raction, Mössbauer spectroscopy, and magnetoelectric effect measurements. As it was proved by X-ray di raction studies the single-phase Bi5Ti3FeO15 compound was obtained. The Mössbauer investigations revealed paramagnetic character of the compound at room temperature as well as at 80 K. Magnetoelectric measurements were carried out at room temperature using lock-in dynamic method and they proved presence of magnetoelectric coupling in this material. Additional magnetoelectric studies were carried out after subsequent electric poling of the sample. It was found that the maximum value of the coupling coe cient was almost twice bigger than in the case without the initial poling and reached a value of ME 20.7 mV cm1 Oe1

Subadditivity of the minimum output entropy and superactivation of the classical capacity of quantum multiple access channels

We study subadditivity of the minimum output entropy ($H_{min}$) of quantum multiple access channels (MACs). We provide an example of violation of the additivity theorem for $H_{min}$ known in classical information theory. Our result is based on a fundamental property of $MACs$ i.e. independence of each sender. The channels used in the example can be constructed explicitly. On the basis of subadditivity of $H_{min}$ we also provide an example of extremal superadditivity (super activation) of the classical capacity region of MACs.Comment: 5 pages, 3 figure