Transport of Entanglement Through a Heisenberg-XY Spin Chain

The entanglement dynamics of spin chains is investigated using Heisenberg-XY spin Hamiltonian dynamics. The various measures of two-qubit entanglement are calculated analytically in the time-evolved state starting from initial states with no entanglement and exactly one pair of maximally-entangled qubits. The localizable entanglement between a pair of qubits at the end of chain captures the essential features of entanglement transport across the chain, and it displays the difference between an initial state with no entanglement and an initial state with one pair of maximally-entangled qubits.Comment: 5 Pages. 3 Figure

Enhancing the photomixing efficiency of optoelectronic devices in the terahertz regime

A method to reduce the transit time of majority of carriers in photomixers and photo detectors to $< 1$ ps is proposed. Enhanced optical fields associated with surface plasmon polaritons, coupled with velocity overshoot phenomenon results in net decrease of transit time of carriers. As an example, model calculations demonstrating $> 280\times$ (or $\sim$2800 and 31.8 $\mu$W at 1 and 5 THz respectively) improvement in THz power generation efficiency of a photomixer based on Low Temperature grown GaAs are presented. Due to minimal dependence on the carrier recombination time, it is anticipated that the proposed method paves the way for enhancing the speed and efficiency of photomixers and detectors covering UV to far infrared communications wavelengths (300 to 1600 nm).Comment: 5 pages, 4 figure

Slow dynamics of interacting antiferromagnetic nanoparticles

We study magnetic relaxation dynamics, memory and aging effects in interacting polydisperse antiferromagnetic NiO nanoparticles by solving a master equation using a two-state model. We investigate the effects of interactions using dipolar, Nearest-Neighbour Short-Range (NNSR) and Long-Range Mean-Field (LRMF) interactions. The magnetic relaxation of the nanoparticles in a time-dependent magnetic field has been studied using LRMF interaction. The size-dependent effects are suppressed in the ac-susceptibility, as the frequency is increased. We find that the memory dip, that quantifies the memory effect is about the same as that of non-interacting nanoparticles for the NNSR case. There is a stronger memory-dip for LRMF, and a weaker memory-dip for the dipolar interactions. We have also shown a memory effect in the Zero-field-cooled magnetization for the dipolar case, a signature of glassy behaviour, from Monte-Carlo studies.Comment: 14 pages, 9 figure