947 research outputs found
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 Kohlbergâs theory of Cognitive Moral Development (CMD) in non-Western contexts by investigating the ethical values of IT professionals in Asiaâs 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 âŒ2 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 âŒ30-20 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 âŒ15 Ma along the western/central fault segment before initiating at least by 10-8 Ma along the eastern fault tip. We relate an âŒ250 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
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