Entanglement changing power of two-qubit unitary operations

We consider a two-qubit unitary operation along with arbitrary local unitary operations acts on a two-qubit pure state, whose entanglement is C_0. We give the conditions that the final state can be maximally entangled and be non-entangled. When the final state can not be maximally entangled, we give the maximal entanglement C_max it can reach. When the final state can not be non-entangled, we give the minimal entanglement C_min it can reach. We think C_max and C_min represent the entanglement changing power of two-qubit unitary operations. According to this power we define an order of gates.Comment: 11 page

Acoustic Attenuation by Two-dimensional Arrays of Rigid Cylinders

In this Letter, we present a theoretical analysis of the acoustic transmission through two-dimensional arrays of straight rigid cylinders placed parallelly in the air. Both periodic and completely random arrangements of the cylinders are considered. The results for the sound attenuation through the periodic arrays are shown to be in a remarkable agreement with the reported experimental data. As the arrangement of the cylinders is randomized, the transmission is significantly reduced for a wider range of frequencies. For the periodic arrays, the acoustic band structures are computed by the plane-wave expansion method and are also shown to agree with previous results.Comment: 4 pages, 3 figure

The signature of subsurface Kondo impurities in the local tunnel current

The conductance of a tunnel point-contact in an STM-like geometry having a single defect placed below the surface is investigated theoretically. The effect of multiple electron scattering by the defect after reflections by the metal surface is taken into account. In the approximation of s-wave scattering the dependence of the conductance on the applied voltage and the position of the defect is obtained. The results are illustrated for a model s-wave phase shift describing Kondo-resonance scattering. We demonstrate that multiple electron scattering by the magnetic impurity plays a decisive role in the point-contact conductance at voltages near the Kondo resonance. We find that the sign and shape of the Kondo anomaly depends on the position of the defect.Comment: 13 pages, 4 figures. To be published in J. Phys.: Cond. Ma

Broken symmetry, excitons, gapless modes and topological excitations in Trilayer Quantum Hall systems

We study the interlayer coherent incompressible phase in Trilayer Quantum Hall systems (TLQH) at total filling factor $\nu_{T}=1$ from three approaches: Mutual Composite Fermion (MCF), Composite Boson (CB) and wavefunction approach. Just like in Bilayer Quantum Hall system, CB approach is superior than MCF approach in studying TLQH with broken symmetry. The Hall and Hall drag resistivities are found to be quantized at $h/e^{2}$. Two neutral gapless modes with linear dispersion relations are identified and the ratio of the two velocities is close to $\sqrt{3}$. The novel excitation spectra are classified into two classes: Charge neutral bosonic 2-body bound states and Charge $\pm 1$ fermionic 3-body bound states. In general, there are two 2-body Kosterlize-Thouless (KT) transition temperatures and one 3-body KT transition. The Charge $\pm 1$ 3-body fermionic bound states may be the main dissipation source of transport measurements. The broken symmetry in terms of $SU(3)$ algebra is studied. The structure of excitons and their flowing patterns are given. The coupling between the two Goldstone modes may lead to the broadening in the zero-bias peak in the interlayer correlated tunnelings of the TLQH. Several interesting features unique to TLQH are outlined. Limitations of the CB approach are also pointed out.Comment: 10 pages, 3 figures, Final version to be published in Phys. Rev.

Mode-coupling and polar nanoregions in the relaxor ferroelectric Pb(Mg1/3Nb2/3)O3

We present a quantitative analysis of the phonon lineshapes obtained by neutron inelastic scattering methods in the relaxor ferroelectric Pb(Mg1/3Nb2/3)O3 (PMN). Differences in the shapes and apparent positions of the transverse acoustic (TA) and transverse optic (TO) phonon peaks measured in the (300) and (200) Brillouin zones at 690 K are well described by a simple model that couples the TA and soft TO modes in which the primary parameter is the wave vector and temperature-dependent TO linewidth Gamma(q,T). This mode-coupling picture provides a natural explanation for the uniform displacements of the polar nanoregions, discovered by Hirota et al., as the PNR result from the condensation of a soft TO mode that also contains a large acoustic component.Comment: 9 pages, 8 figure

Growth of aligned carbon nanotubes on carbon microfibers by dc plasma-enhanced chemical vapor deposition

It is shown that unidirectionally aligned carbon nanotubes can be grown on electrically conductive network of carbon microfibers via control of buffer layer material and applied electric field during dc plasma chemical vapor deposition growth. Ni catalyst deposition on carbon microfiber produces relatively poorly aligned nanotubes with significantly varying diameters and lengths obtained. The insertion of Ti 5 nm thick underlayer between Ni catalyst layer and C microfiber substrate significantly alters the morphology of nanotubes, resulting in much better aligned, finer diameter, and longer array of nanotubes. This beneficial effect is attributed to the reduced reaction between Ni and carbon paper, as well as prevention of plasma etching of carbon paper by inserting a Ti buffer layer. Such a unidirectionally aligned nanotube structure on an open-pore conductive substrate structure may conveniently be utilized as a high-surface-area base electrodes for fuel cells, batteries, and other electrochemical and catalytic reactions

Real-time cavity QED with single atoms

We report the first measurement of the real-time evolution of the complex field amplitude brought on by single atom transits. We show the variation in time of both quadrature amplitudes (simultaneously recorded) of the light transmitted through the cavity, as well the resultant optical phase for a single atom transit event. In this particular measurement, the cavity and laser were both detuned by 10 MHz from the Cs resonance

ϕ\phi-meson production at forward/backward rapidity in high-energy nuclear collisions from a multiphase transport model

Within the framework of a multiphase transport model (AMPT), the $\phi$-meson production is studied in d+Au collisions at \srt = {200} GeV in the forward (d-going, $1.2<y<2.2$) and backward (Au-going, $-2.2<y<-1.2$) direction. The AMPT model with string melting version (parton cascade turning-on) describes the experimental data well, while the pure hadronic transport scenario of the AMPT model underestimates the $\phi$-meson production rate in comparison with the data. Detailed investigations including the rapidity, transverse momentum and collision system size dependencies of $\phi$-meson nuclear modification factor indicate that a combination of the initial state effect and a follow-up parton cascade is required in the AMPT model to describe the data. Similar calculations are also present in p+Pb collisions at \srt = {5.02} TeV and p+p collisions at \srt = {2.76} TeV. The findings from a comparison of AMPT model study with the data are consistent with that at RHIC energy.Comment: 5 pages, 5 figure