Indistinguishable Encoding for Bidirectional Quantum Key Distribution: Theory to Experiment

We present for the first time, a bidirectional Quantum Key Distribution protocol with minimal encoding operations derived from the use of two `nonorthogonal' unitary transformations selected from two mutually unbiased unitary bases; which are indistinguishable in principle for a single use. Along with its decoding procedure, it is a stark contrast to its `orthogonal encoding' predecessors. Defining a more relevant notion of security threshold for such protocols, the current protocol outperforms its predecessor in terms of security as the maximal amount of information an eavesdropper can glean is essentially limited by the indistinguishability of the transformations. We further propose adaptations for a practical scenario and report on a proof of concept experimental scheme based on polarised photons from an attenuated pulsed laser for qubits, demonstrating the feasibility of such a protocol.Comment: 9 pages, 3 figure

Blind encoding into qudits

We consider the problem of encoding classical information into unknown qudit states belonging to any basis, of a maximal set of mutually unbiased bases, by one party and then decoding by another party who has perfect knowledge of the basis. Working with qudits of prime dimensions, we point out a no-go theorem that forbids shift operations on arbitrary unknown states. We then provide the necessary conditions for reliable encoding/decoding.Comment: To appear in Physics Letters

Entropic bounds as uncertainty measure of unitary operators

We reformulate the notion of uncertainty of pairs of unitary operators within the context of guessing games and derive an entropic uncertainty relation for a pair of such operators. We show how distinguishable operators are compatible while maximal incompatibility of unitary operators can be connected to bases for some subspace of operators which are mutually unbiased

Giant magnetoresistance in granular cobalt copper thin films prepared by pulsed laser ablation deposition

Giant magnetoresistance of up to 9.5% in 1.5 T at 14 K has been observed in Co19Cu81, thin films prepared by pulsed laser ablation deposition from rotated, split targets. The as-grown films show a small GMR effect but this may be enhanced by a factor of 4 by appropriate annealing. The volume ratio of material in the target is found to be reproduced in the film. Measurements of the remanence and initial susceptibility of the films indicate a distribution of energy barriers to the rotation of the magnetic moments of the cobalt particles and also the presence of inter-particle interactions. The choice of operating parameters to control these effects and thus optimise the GMR is discussed

Linear acenes linked thiophene, electronic and chemical properties: Prospects for molecular organic electronic material

We report a theoretical study of linear acene (n=1 to 7) linked thiophene properties functionality. The total ground state and band gap energies, Coulomb potential and nuclear repulsion energy are calculated by DFT, MP2 at B3LYP exchange level of the theory and 6-311G* basis set. The results are in good agreement with the experimental and theoretical values. It is found that the total ground state energy of the system and band gap energy decreases with an increasing number of electrons in the rings. The addition of thiophene molecules tends to improve the electronic and chemical properties of the linear acenes, the material exhibit potential application in the organic molecular electronic material

Magnetoresistive and magnetic properties of La0.67A0.33MnO3 (A= Ba, Ca, and Sr) prepared by co-precipitation method.

We have prepared perovskite structured La0.67A0.33MnO3 manganite (A = Ba, Ca and Sr) using co-precipitation method. The samples were characterized using x-ray diffraction (XRD) and scanning electron microscope (SEM) to identify the structure and microstructure. The magnetic and magnetoresistance properties were measured by vibrations sample magnetometer (VSM) and four point probe methods. From the XRD spectrum, samples are in single phase pervoskite structure where LBMO and LCMO showed orthorhombic whereas LSMO has rhombohedral phase. LSMO has average grain size range of 0.5μm -2.5μm. However, for LBMO and LCMO, the grain boundaries are not well define and connected. The difference in the microstructure image might be due to the different activation energy and variance A-site cation that differs in grain growth. The Curie temperature of LBMO and LSMO are 343K and 371K, respectively. LCMO system gives the highest CMR value (-10.1% at 1 tesla) at room temperature. A significantly low field magnetoresistance effect (LFMR) which is -13.9% (at 0.1T, 90K) has been observed in LBMO and this LFMR effect is believed to be due to the disorder layers at the grain boundaries in the samples