4,348 research outputs found
Magnetic Order in Kondo-Lattice Systems due to Electron-Electron Interactions
The hyperfine interaction between the electron spin and the nuclear spins is
one of the main sources of decoherence for spin qubits when the nuclear spins
are disordered. An ordering of the latter largely suppresses this source of
decoherence. Here we show that such an ordering can occur through a
thermodynamic phase transition in two-dimensional (2D) Kondo-lattice type
systems. We specifically focus on nuclear spins embedded in a 2D electron gas.
The nuclear spins interact with each other through the RKKY interaction, which
is carried by the electron gas. We show that a nuclear magnetic order at finite
temperature relies on the anomalous behavior of the 2D static electron spin
susceptibility due to electron-electron interactions. This provides a
connection between low-dimensional magnetism and non-analyticities in
interacting 2D electron systems. We discuss the conditions for nuclear
magnetism, and show that the associated Curie temperature increases with the
electron-electron interactions and may reach up into the millikelvin regime.
The further reduction of dimensionality to one dimension is shortly discussed.Comment: Proceedings for 2nd International Workshop on Solid-State Quantum
Computing (Taipei, Taiwan, June 2008); 6 pages, 2 figure
An Architecture for Provenance Systems
This document covers the logical and process architectures of provenance systems. The logical architecture identifies key roles and their interactions, whereas the process architecture discusses distribution and security. A fundamental aspect of our presentation is its technology-independent nature, which makes it reusable: the principles that are exposed in this document may be applied to different technologies
Integrating nuclide specific and dose rate based methods for airborne and ground based gamma spectrometry
Results of joint airborne survey work conducted by SUERC and JAEA are presented, for areas to the north and south of Fukushima Daiichi using four different airborne survey systems, cross calibrated at reference sites in Scotland and near Namie. Airborne measurements were made at a series of different survey heights using three high volume NaI based spectrometers, and for the first time using a high resolution system based on the Ortec IDM HPGe spectrometer. The JAEA data sets were analysed using the same methods applied to national scale mapping in Japan since the accident. The SUERC data sets were analysed using nuclide specific approaches validated in the European ECCOMAGS project. The data presented on a digital terrain model show marked correspondence with landscape features, which both suggest the initial deposition processes, and indicate trajectories for future re-deposition by natural processes. All data sets are traceable to each other, and to the ground based calibration sites. Nuclide specific inventories have been defined, which can serve as a future reference to evaluate environmental change
Single-photon-assisted entanglement concentration of a multi-photon system in a partially entangled W state with weak cross-Kerr nonlinearity
We propose a nonlocal entanglement concentration protocol (ECP) for
-photon systems in a partially entangled W state, resorting to some
ancillary single photons and the parity-check measurement based on cross-Kerr
nonlinearity. One party in quantum communication first performs a parity-check
measurement on her photon in an -photon system and an ancillary photon, and
then she picks up the even-parity instance for obtaining the standard W state.
When she obtains an odd-parity instance, the system is in a less-entanglement
state and it is the resource in the next round of entanglement concentration.
By iterating the entanglement concentration process several times, the present
ECP has the total success probability approaching to the limit in theory. The
present ECP has the advantage of a high success probability. Moreover, the
present ECP requires only the -photon system itself and some ancillary
single photons, not two copies of the systems, which decreases the difficulty
of its implementation largely in experiment. It maybe have good applications in
quantum communication in future.Comment: 7 pages, 3 figure
Efficient scheme for three-photon Greenberger-Horne-Zeilinger state generation
We propose an efficient scheme for the generation of three-photon
Greenberger-Horne-Zeilinger (GHZ) state with linear optics and postselection.
Several devices are designed and a two-mode quantum nondemolition (QND)
detection is introduced to obtain the desired state. It is worth noting that
the states which have entanglement in both polarization and spatial degrees of
freedom are created in one of the designed setups. The method described in the
present scheme can create a large number of three-photon GHZ states in
principle. We also discuss an approach to generate the desired GHZ state in the
presence of channel noise.Comment: 7pages, 3 figure
Cross-Kerr nonlinearity between continuous-mode coherent states and single photons
Weak cross-Kerr nonlinearities between single photons and coherent states are
the basis for many applications in quantum information processing. These
nonlinearities have so far mainly been discussed in terms of highly idealized
single-mode models. We develop a general theory of the interaction between
continuous-mode photonic pulses and apply it to the case of a single photon
interacting with a coherent state. We quantitatively study the validity of the
usual single-mode approximation using the concepts of fidelity and conditional
phase. We show that high fidelities, non-zero conditional phases and high
photon numbers are compatible, under conditions where the pulses fully pass
through each other and where unwanted transverse-mode effects are suppressed.Comment: 8 pages, 2 figures, more general results in section V
Investigation into pulse sequence analysis of PD features due to electrical tree growth in epoxy resin
Electrical trees developed using point-plane samples have been investigated under three different voltage conditions: AC, AC with positive DC bias, and AC with negative DC bias. Visual observations mainly indicate two types of electrical tree progression from initiation to breakdown: āforward and backwardā (FB) trees and "forward" (F) trees. FB trees can be observed in AC tests, while F trees occur in AC with DC bias tests. The difference between AC with negative DC bias and AC with positive DC bias is the growth of a rapid long branch prior to breakdown under negative DC bias conditions. Based on the pulse sequence analysis (PSA) technique applied to the PD data associated with electrical tree growth, the findings confirm that PSA curves under different voltage tests have different regions and PSA features can be indicators of tree growth
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