1,721,031 research outputs found
Time evolution of tripartite quantum discord and entanglement under local and nonlocal random telegraph noise
No full textFew studies explored the dynamics of nonclassical correlations besides entanglement in open multipartite
quantum systems. Here, we address the time evolution of quantum discord and entanglement in a model of
three noninteracting qubits subject to a classical random telegraph noise in common and separated environments.
Two initial entangled states of the system are examined, namely the GHZ- and W-type states. The dynamics
of quantum correlations results to be strongly affected by the input configuration of the qubits, the type of the
system-environment interaction, and the memory properties of the environmental noise. When the qubits are
nonlocally coupled to the random telegraph noise, the GHZ-type states partially preserve, at long times, both
discord and entanglement, regardless of the correlation time of the environmental noise. The survived entangled
states turn out to be also detectable by means of suitable entanglement witnesses. On the other hand, in the same
conditions, the decohering effects suppress all the quantum correlation of the W-type states which are thus less
robust than the GHZ-type ones. The long-time survival of tripartite discord and entanglement opens interesting
perspectives in the use of multipartite entangled states for practical applications in quantum information science
Non locality and causal evolution in QFT
No full textNon-locality appearing in QFT during the free evolution of localized field states and in the Feynman propagator function is analysed. It is shown to be connected to the initial non-local properties present at the level of quantum states and it does not imply a violation of Einstein's causality. Then a simple QFT system with interaction, consisting of a classical source coupled linearly to a quantum scalar field is investigated and is exactly solved. The expression for the time evolution of the state describing the system is given. The expectation value of any arbitrary 'good' local observable, expressed as a function of the field operator and its space and time derivatives, is obtained explicitly at all orders in the field-matter coupling constant. These expectation values have a source-dependent part that is shown to be always causally retarded, while the non-local contributions are source independent and related to the non-local properties of zero-point vacuum fluctuation
Localization in a QFT model
No full textLocalization properties of a QFT model, consisting of a quantum scalar field interacting linearly with a classical localized source, are investigated using various approaches present in the literature. We evaluate, to any order of the field–matter coupling constant, the time evolution of average values of one-point localization observables and scalar product between the quantum field state of the evolving system and localized states. We show that the appearance of nonlocality can be connected to nonlocal properties of localized states used or to the fact that localization operators do not satisfy the microcausality principle and therefore does not imply the violation of causalit
Entanglement Creation for Two-Electron Scattering in a 2D System
No full textRecently great attention has been addressed to the study of quantum correlations in systems of identical particles. Various definitions of entanglement for indistinguishable particles are present in the literature. Following Schliemann’s theory, here we perform a quantitative evaluation of the entanglement dynamics for electron-electron scattering in a 2D system in terms of the von Neumann entropy of the reduced one-particle density matrix. Our approach allows us to define the time of entanglement formation and to investigate the role of the space and spin degrees of freedom in the building up of quantum correlations
On demand entanglement in double quantum dots via coherent carrier scattering
No full textWe show how two qubits encoded in the orbital states of two quantum dots can be entangled or disentangled in a controlled way through their interaction with a weak electron current. The transmission/reflection spectrum of each scattered electron, acting as an entanglement mediator between the dots, shows a signature of the dot–dot entangled state. Strikingly, while a few scattered carriers produce decoherence of the whole two-dot system, a larger number of electrons injected from one lead with proper energy are able to recover its quantum coherence. Our numerical simulations are based on a real-space solution of the three-particle Schrödinger equation with open boundaries. The computed transmission amplitudes are inserted in the analytical expression for the system density matrix to evaluate the entanglement
Effects of scattering resonances on carrier-carrier entanglement in charged quantum dots
No full textWe address the problem of the entanglement generationin an electron-scattering by a 1D double-barrier resonanttunnelling device. In particular we analyze the roleplayed by transport resonances in the appearance of quantumcorrelations between the energy states of the electrons.The entanglement is not sensitive to the presence of Breit-Wigner resonances, while it may be controlled by manipulatingFano resonances. Such a behavior is ascribed tothe different mechanisms characterizing the two types of processes
Carrier-carrier entanglement and transport resonances in semiconductor quantum dots
Full text linkWe study theoretically the entanglement created in a scattering between an electron, incoming from a source lead, and another electron bound in the ground state of a quantum dot, connected to two leads. We analyze the role played by the different kinds of resonances in the transmission spectra and by the number of scattering channels, into the amount of quantum correlations between the two identical carriers. It is shown that the entanglement between their energy states is not sensitive to the presence of Breit-Wigner resonances, while it presents a peculiar behavior in correspondence to Fano peaks: two close maxima separated by a minimum for a two-channel scattering and a single maximum for a multichannel scattering. Such a behavior is ascribed to the different mechanisms characterizing the two types of resonances. Our results suggest that the production and detection of entanglement in quantum dot structures may be controlled by the manipulation of Fano resonances through external fields
Simulation of the entanglement creation for identical particles scattering in a 2D system
No full textIn recent years the dynamics of entanglement formation between two distinguishable charged particles has been investigated for scattering events in bulk semiconductors. The aim of this work is to overcome the hypothesis of distinguishable carriers. Here we present a quantitative evaluation of the entanglement dynamics for electron-electron collisions in a 2D system applying a method, suitable for indistinguishable particles, based on the Slater rank and the von Neumann entropy of the reduced density matrix. The quantum entanglement of both spatial and spin degrees of freedom is computed for various initial conditions of the system
Quantum teleportation of electrons in quantum wires with surface acoustic waves
Full text linkWe propose and numerically simulate a semiconductor device based on coupled quantum wires, suitable for deterministic quantum teleportation of electrons trapped in the minima of surface acoustic waves. We exploit a network of interacting semiconductor quantum wires able to provide the universal set of gates for quantum information processing with the qubit defined by the localization of a single electron in one of two coupled channels. The numerical approach is based on a time-dependent solution of the three-particle Schrödinger equation. First, a maximally entangled pair of electrons is obtained via Coulomb interaction between carriers in different channels. Then, a complete Bell-state measurement involving one electron from this pair and a third electron is performed. Finally, the teleported state is reconstructed by means of local one-qubit operations. The large estimated fidelity explicitly suggests that an efficient teleportation process could be reached in an experimental setup
Entanglement dynamics of electron-electron scattering in low-dimensional semiconductor systems
No full textWe perform the quantitative evaluation of the entanglement dynamics in scattering events between two indistinguishable electrons interacting via the Coulomb potential in one- and two-dimensional semiconductor nanostructures. We apply a criterion based on the von Neumann entropy and the Schmidt decomposition of the global state vector suitable for systems of identical particles. From the time-dependent numerical solution of the two-particle wave function of the scattering carriers we compute their entanglement evolution for different spin configurations: two electrons with the same spin, with different spin, and singlet and triplet spin states. The procedure allows us to evaluate the mechanisms that govern entanglement creation and their connection with the characteristic physical parameters and initial conditions of the system. The cases in which the evolution of entanglement is similar to the one obtained for distinguishable particles are discussed
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