2,560 research outputs found
Entanglement swapping between electromagnetic field modes and matter qubits
Scalable quantum networks require the capability to create, store and
distribute entanglement among distant nodes (atoms, trapped ions, charge and
spin qubits built on quantum dots, etc.) by means of photonic channels. We show
how the entanglement between qubits and electromagnetic field modes allows
generation of entangled states of remotely located qubits. We present
analytical calculations of linear entropy and the density matrix for the
entangled qubits for the system described by the Jaynes-Cummings model. We also
discuss the influence of decoherence. The presented scheme is able to drive an
initially separable state of two qubits into an highly entangled state suitable
for quantum information processing
Entanglement of flux qubits through a joint detection of photons
We study the entanglement creation between two flux qubits interacting with
electromagnetic field modes. No direct interaction between the qubits exists.
Entanglement is reached using entanglement swapping method by an interference
measurement performed on photons. We discuss the influence of off-resonance and
multi-photon initial states on the qubit-qubit entanglement. The presented
scheme is able to drive an initially separable state of two qubits into an
highly entangled state suitable for quantum information processing.Comment: 4 pages, 5 figure
The Two-fluid Description of a Mesoscopic Cylinder
Quantum coherence of electrons interacting via the magnetostatic coupling and
confined to a mesoscopic cylinder is discussed.
The electromagnetic response of a system is studied. It is shown that the
electromagnetic kernel has finite low frequency limit what implies infinite
conductivity. It means that part of the electrons is in a coherent state and
the system can be in general described by a two-fluid model.
The coherent behavior is determind by the interplay between finite size
effects and the correlations coming from the magnetostatic interactions (the
interaction is considered in the mean field approximation).
The related persistent currents depend on the geometry of the Fermi Surface.
If the Fermi Surface has some flat portions the self-sustaining currents can be
obtained.
The relation of the quantum coherent state in mesoscopic cylinders to other
coherent phenomena is discussed.Comment: 21 pages, Latex, 4 figures, in print in Eur. Phys. J. B (Z. Phys. B
Coherence of Currents in Mesoscopic Cylinders
The persistent currents driven by the pure Aharonov-Bohm type magnetic field
in mesoscopic normal metal or semiconducting cylinders are studied. A
two-dimensional (2D) Fermi surfaces are characterized by four parameters.
Several conditions for the coherence and enhancement of currents are discussed.
These results are then generalized to a three-dimensional (3D) thin-walled
cylinder to show that under certain geometric conditions on the Fermi surface,
a novel effect - the appearance of spontaneous currents is predicted.Comment: 17 pages, Latex, 8 figures available on request, to be published in
Z.Physik
Semiconductor quantum ring as a solid-state spin qubit
The implementation of a spin qubit in a quantum ring occupied by one or a few
electrons is proposed. Quantum bit involves the Zeeman sublevels of the highest
occupied orbital. Such a qubit can be initialized, addressed, manipulated, read
out and coherently coupled to other quantum rings. An extensive discussion of
relaxation and decoherence is presented. By analogy with quantum dots, the spin
relaxation times due to spin-orbit interaction for experimentally accessible
quantum ring architectures are calculated. The conditions are formulated under
which qubits build on quantum rings can have long relaxation times of the order
of seconds. Rapidly improving nanofabrication technology have made such ring
devices experimentally feasible and thus promising for quantum state
engineering.Comment: 16 pages, 3 figure 3 table
Wave function engineering in quantum dot-ring nanostructures
Modern nanotechnology allows producing, depending on application, various
quantum nanostructures with the desired properties. These properties are
strongly influenced by the confinement potential which can be modified, e.g.,
by electrical gating. In this paper we analyze a nanostructure composed of a
quantum dot surrounded by a quantum ring. We show that depending on the details
of the confining potential the electron wave functions can be located in
different parts of the structure. Since the properties of such a nanostructure
strongly depend on the distribution of the wave functions, varying the applied
gate voltage one can easily control them. In particular, we illustrate the high
controllability of the nanostructure by demonstrating how its coherent,
optical, and conducting properties can be drastically changed by a small
modification of the confining potential.Comment: 8 pages, 10 figures, 2 tables, revte
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