Study of Loschmidt Echo for a qubit coupled to an XY-spin chain environment

We study the temporal evolution of a central spin-1/2 (qubit) coupled to the environment which is chosen to be a spin-1/2 transverse XY spin chain. We explore the entire phase diagram of the spin-Hamiltonian and investigate the behavior of Loschmidt echo(LE) close to critical and multicritical point(MCP). To achieve this, the qubit is coupled to the spin chain through the anisotropy term as well as one of the interaction terms. Our study reveals that the echo has a faster decay with the system size (in the short time limit) close to a MCP and also the scaling obeyed by the quasiperiod of the collapse and revival of the LE is different in comparison to that close to a QCP. We also show that even when approached along the gapless critical line, the scaling of the LE is determined by the MCP where the energy gap shows a faster decay with the system size. This claim is verified by studying the short-time and also the collapse and revival behavior of the LE at a quasicritical point on the ferromagnetic side of the MCP. We also connect our observation to the decoherence of the central spin.Comment: Accepted for publication in EPJ

The Ethics of IT Professionals in Japan and China

The ethical integrity and accountability of Information Technology (IT) professionals is important given our reliance on various forms of IT. We examined the applicability of Lawrence Kohlberg’s theory of Cognitive Moral Development (CMD) in non-Western contexts by investigating the ethical values of IT professionals in Asia’s two largest economies. Analysis of survey data from Japan (n=289) and China (n=290) indicates support for the basic six-stage model of CMD. The concept of abiding by universal laws and rules (termed stage 4 reasoning by Kohlberg) was widely accepted by IT professionals in both Japan and China, despite the Confucian cultural emphasis on personal relationships with particularistic obligations. However, differences between Japanese and Chinese IT professionals were found while, in direct contrast with the stage-wise theory of CMD, the respondents from Japan and especially China exhibited significant volatility, reasoning at different stages simultaneously. The implications of these findings for research and practice are discussed

Decoherence of molecular wave packets in an anharmonic potential

The time evolution of anharmonic molecular wave packets is investigated under the influence of the environment consisting of harmonic oscillators. These oscillators represent photon or phonon modes and assumed to be in thermal equilibrium. Our model explicitly incorporates the fact that in the case of a nonequidistant spectrum the rates of the environment induced transitions are different for each transition. The nonunitary time evolution is visualized by the aid of the Wigner function related to the vibrational state of the molecule. The time scale of decoherence is much shorter than that of dissipation, and gives rise to states which are mixtures of localized states along the phase space orbit of the corresponding classical particle. This behavior is to a large extent independent of the coupling strength, the temperature of the environment and also of the initial state.Comment: 7 pages, 4 figure

Exact Master Equation and Non-Markovian Decoherence for Quantum Dot Quantum Computing

In this article, we report the recent progress on decoherence dynamics of electrons in quantum dot quantum computing systems using the exact master equation we derived recently based on the Feynman-Vernon influence functional approach. The exact master equation is valid for general nanostructure systems coupled to multi-reservoirs with arbitrary spectral densities, temperatures and biases. We take the double quantum dot charge qubit system as a specific example, and discuss in details the decoherence dynamics of the charge qubit under coherence controls. The decoherence dynamics risen from the entanglement between the system and the environment is mainly non-Markovian. We further discuss the decoherence of the double-dot charge qubit induced by quantum point contact (QPC) measurement where the master equation is re-derived using the Keldysh non-equilibrium Green function technique due to the non-linear coupling between the charge qubit and the QPC. The non-Markovian decoherence dynamics in the measurement processes is extensively discussed as well.Comment: 15 pages, Invited article for the special issue "Quantum Decoherence and Entanglement" in Quantum Inf. Proces

Long-distance quantum communication with "polarization" maximally entangled states

We propose a scheme for long-distance quantum communication where the elementary entanglement is generated through two-photon interference and quantum swapping is performed through one-photon interference. Local "polarization" maximally entangled states of atomic ensembles are generated by absorbing a single photon from on-demand single-photon sources. This scheme is robust against phase fluctuations in the quantum channels, moreover speeds up long-distance high-fidelity entanglement generation rate.Comment: 5 pages 5 figure

Expression, crystallization and preliminary X-ray diffraction studies of N-carbamyl-D-amino-acid amidohydrolase from Agrobacterium radiobacter

The Agrobacterium radiobacter CCRC 14924 N-carbamyl-D-amino-acid amidohydrolase, the enzyme used for production of D-amino acids, was overexpressed in Escherichia coli JM109. The expressed protein was crystallized by vapour diffusion using lithium sulfate as precipitant. It crystallizes in space group P2(1) with unit-cell parameters cr = 69.8, b = 67.9 and c = 137.8 Angstrom and beta = 96.4 degrees. There are four molecules per asymmetric unit. Crystals diffract to 2.8 Angstrom resolution using a rotating-anode source at cryogenic (113 K) temperatures

Rates and style of Cenozoic deformation around the Gonghe basin, northeastern Tibetan Plateau

The northeastern Tibetan Plateau constitutes a transitional region between the lowrelief physiographic plateau to the south and the high-relief ranges of the Qilian Shan to the north. Cenozoic deformation across this margin of the plateau is associated with localized growth of fault-cored mountain ranges and associated basins. Herein, we combine detailed structural analysis of the geometry of range-bounding faults and deformation of foreland basin strata with geomorphic and exhumational records of erosion in hangingwall ranges in order to investigate the magnitude, timing, and style of deformation along the two primary fault systems, the Qinghai Nan Shan and the Gonghe Nan Shan. Structural mapping shows that both ranges have developed above imbricate fans of listric thrust faults, which sole into décollements in the middle crust. Restoration of shortening along balanced cross sections suggests a minimum of 0.8-2.2 km and 5.1-6.9 km of shortening, respectively. Growth strata in the associated foreland basin record the onset of deformation on the two fault systems at ca. 6-10 Ma and ca. 7-10 Ma, respectively, and thus our analysis suggests late Cenozoic shortening rates of 0.2 +0.2/-0.1 km/m.y. and 0.7 +0.3/-0.2 km/m.y. along the north and south sides of Gonghe Basin. Along the Qinghai Nan Shan, these rates are similar to late Pleistocene slip rates of ~0.10 ± 0.04 mm/yr, derived from restoration and dating of a deformed alluvial-fan surface. Collectively, our results imply that deformation along both flanks of the doubly vergent Qilian Shan-Nan Shan initiated by ca. 10 Ma and that subsequent shortening has been relatively steady since that time

Low-temperature thermochronometry along the Kunlun and Haiyuan Faults, NE Tibetan Plateau: Evidence for kinematic change during late-stage orogenesis

The Tibetan Plateau is a prime example of a collisional orogen with widespread strike-slip faults whose age and tectonic significance remain controversial. We present new low-temperature thermochronometry to date periods of exhumation associated with Kunlun and Haiyuan faulting, two major strike-slip faults within the northeastern margin of Tibet. Apatite and zircon (U-Th)/He and apatite fission-track ages, which record exhumation from ∼2 to 6 km crustal depths, provide minimum bounds on fault timing. Results from Kunlun samples show increased exhumation rates along the western fault segment at circa 12-8 Ma with a possible earlier phase of motion from ∼30-20 Ma, along the central fault segment at circa 20-15 Ma, and along the eastern fault segment at circa 8-5 Ma. Combined with previous studies, our results suggest that motion along the Haiyuan fault may have occurred as early as ∼15 Ma along the western/central fault segment before initiating at least by 10-8 Ma along the eastern fault tip. We relate an ∼250 km wide zone of transpressional shear to synchronous Kunlun and Haiyuan fault motion and suggest that the present-day configuration of active faults along the northeastern margin of Tibet was likely established since middle Miocene time. We interpret the onset of transpression to relate to the progressive confinement of Tibet against rigid crustal blocks to the north and expansion of crustal thickening to the east during the later stages of orogen development. Key Points Low-T thermochronometry dates periods of exhumation along NE Tibet faults Left-lateral faulting by mid-to-late Miocene along the Kunlun and Haiyuan Faults Shift to widespread lateral faulting in late stage of Tibet collisional histor

The effect of grain size on electrical transport and magnetic properties of La0.9Te0.1MnO3

The effect of grain size on structural, magnetic and transport properties in electron-doped manganites La0.9Te0.1MnO3 has been investigated. All samples show a rhombohedral structure with the space group at room temperature. It shows that the Mn-O-Mn bond angle decreases and the Mn-O bond length increases with the increase of grain size. All samples undergo paramagnetic (PM)-ferromagnetic (FM) phase transition and an interesting phenomenon that both magnetization and the Curie temperature decrease with increasing grain size is observed, which is suggested to mainly originate from the increase of the Mn-O bond length . Additionally, obviously increases with decreasing grain size due to the increase of both the height and width of tunneling barriers with decreasing the grain size. The results indicate that both the intrinsic colossal magnetoresistance (CMR) and the extrinsic the extrinsic interfacial magnetoresistance (IMR) can be effectively tuned in La0.9Te0.1MnO3 by changing grain size.Comment: 15 pages,4 figures. Solid state communications 132(2004)83-8

Relation of a New Interpretation of Stochastic Differential Equations to Ito Process

Stochastic differential equations (SDE) are widely used in modeling stochastic dynamics in literature. However, SDE alone is not enough to determine a unique process. A specified interpretation for stochastic integration is needed. Different interpretations specify different dynamics. Recently, a new interpretation of SDE is put forward by one of us. This interpretation has a built-in Boltzmann-Gibbs distribution and shows the existence of potential function for general processes, which reveals both local and global dynamics. Despite its powerful property, its relation with classical ones in arbitrary dimension remains obscure. In this paper, we will clarify such connection and derive the concise relation between the new interpretation and Ito process. We point out that the derived relation is experimentally testable.Comment: 16 pages, 2 figure