Hahn echo and criticality in spin-chain systems

We establish a relation between Hahn spin-echo of a spin-$\frac 1 2$ particle and quantum phase transition in a spin-chain, which couples to the particle. The Hahn echo is calculated and discussed at zero as well as at finite temperatures. On the example of XY model, we show that the critical points of the chain are marked by the extremal values in the Hahn echo, and influence the Hahn echo in surprising high temperature. An explanation for the relation between the echo and criticality is also presented.Comment: 5 pages, 6 figure

Quantum Critical Dynamics of A Qubit Coupled to An Isotropic Lipkin-Meshkov-Glick Bath

We explore a dynamic signature of quantum phase transition (QPT) in an isotropic Lipkin-Meshkov-Glick (LMG) model by studying the time evolution of a central qubit coupled to it. We evaluate exactly the time-dependent purity, which can be used to measure quantum coherence, of the central qubit. It is found that distinctly different behaviors of the purity as a function of the parameter reveal clearly the QPT point in the system. It is also clarified that the present model is equivalent to an anti Jaynes-Cummings model under certain conditions.Comment: 8 pages, 4 figure

Comparison and analysis of flux-switching permanent-magnet double-rotor machine with 4QT used for HEV

This journal issue contains selected papers from the 2014 IEEE International Magnetics (INTERMAG) ConferenceCQ - Motors, generators and actuators VIpublished_or_final_versio

DEVELOPMENT OF POLYRROLE THIN FILM BASED SOLID-CONTACT ION-SELECTIVE ELECTRODES FOR NITRATE AND NITRITE

Joint Research on Environmental Science and Technology for the Eart

Entanglement in spin-1/2 dimerized Heisenberg systems

We study entanglement in dimerized Heisenberg systems. In particular, we give exact results of ground-state pairwise entanglement for the four-qubit model by identifying a Z_2 symmetry. Although the entanglements cannot identify the critical point of the system, the mean entanglement of nearest-neighbor qubits really does, namely, it reaches a maximum at the critical point.Comment: Four pages, three figures, accepted in Communications in Theoretical Physic

Effect Analysis of Time and Carrier Frequency Offset on the Performance of Distributed Transmit Beamforming for Emergency Radio

In emergency radio scenario, distributed transmit beamforming (DTBF) enables a set of distributed radio nodes to transmit cooperatively to get a better performance. DTBF performance has been analyzed for various node distributions in the literature. However, time offset (TO) and carrier frequency offset (CFO) may exist between transmitting nodes, due to each radio node is equipped with its own clock circuit and local oscillator. Effect analysis of TO and CFO on DTBF performance is an open issue. This paper evaluates the effect of TO and CFO on performance of DTBF for arbitrary node distributions. In this study, TO and CFO are converted into phase offset (PO), and non-parametric kernel method is used to calculate the PDFs of node and offsets. Theoretical analysis and simulation results show that TO and CFO result in degradation of the mainlobe power and affect the beampattern characteristics