60 research outputs found
Entanglement between static and flying qubits in quantum wires
A weakly bound electron in a semiconductor quantum wire is shown to become
entangled with an itinerant electron via the coulomb interaction. The degree of
entanglement and its variation with energy of the injected electron, may be
tuned by choice of spin and initial momentum. Full entanglement is achieved
close to energies where there are spin-dependent resonances. Possible
realisations of related device structures are discussed
Conductance of a molecule with a center of mass motion
We calculate the zero temperature conductance and characteristic correlation
functions of a molecule with a center of mass (CM) motion which modulates
couplings to the leads. In the first model studied, the CM vibrational mode is
simultaneously coupled to the electron density on the molecule. The conductance
is suppressed in regimes corresponding to non-integer occupancy of the
molecule. In the second model, where the CM mode is not directly coupled to the
electron density, the suppression of conductance is related to the dynamic
breaking of the inversion symmetry.Comment: to appear in Phys. Rev.
Kondo effect in triple quantum dots
Numerical analysis of the simplest odd-numbered system of coupled quantum
dots reveals an interplay between magnetic ordering, charge fluctuations and
the tendency of itinerant electrons in the leads to screen magnetic moments.
The transition from local-moment to molecular-orbital behavior is visible in
the evolution of correlation functions as the inter-dot coupling is increased.
Resulting novel Kondo phases are presented in a phase diagram which can be
sampled by measuring the zero-bias conductance. We discuss the origin of the
even-odd effects by comparing with the double quantum dot.Comment: 4 pages, 4 figure
Conductance of deformable molecules with interaction
Zero temperature linear response conductance of molecules with Coulomb
interaction and with various types of phonon modes is analysed together with
local occupation, local moment, charge fluctuations and fluctuations of
molecular deformation. Deformation fluctuations are quantitatively related to
charge fluctuations which exhibit similarity also to static charge
susceptibility.Comment: 4 pages, color figure
Non-adiabatically driven electron in quantum wire with spin-orbit interaction
An exact solution is derived for the wave function of an electron in a
semiconductor quantum wire with spin-orbit interaction and driven by external
time dependent harmonic confining potential. The formalism allows analytical
expressions for various quantities to be derived, such as spin and pseudo-spin
rotations, energy and occupation probabilities for excited states. It is
demonstrated how perfect spin and pseudo-spin flips can be achieved at high
frequencies of order \omega, the confining potential level spacing. By an
appropriately chosen driving term, spin manipulation can be exactly performed
far into the non-adiabatic regime. Implications for spin-polarised emission and
spin-dependent transport are also discussed.Comment: 11 pages, 3 figure
Entanglement between static and flying qubits in a semiconducting carbon nanotube
Entanglement can be generated by two electrons in a spin-zero state on a
semiconducting single-walled carbon nanotube. The two electrons, one weakly
bound in a shallow well in the conduction band, and the other injected into the
conduction band, are coupled by the Coulomb interaction. Both transmission and
entanglement are dependent on the well characteristics, which can be controlled
by a local gate, and on the kinetic energy of the injected electron. Regimes
with different degrees of electron correlation exhibit full or partial
entanglement. In the latter case, the maximum entanglement can be estimated as
a function of width and separation of a pair of singlet-triplet resonances.Comment: 17 pages and 12 figures, accepted to J. Phys. Cond. Ma
Spin-dependent thermoelectric transport coefficients in near-perfect quantum wires
Thermoelectric transport coefficients are determined for semiconductor
quantum wires with weak thickness fluctuations. Such systems exhibit anomalies
in conductance near 1/4 and 3/4 of 2e^2/h on the rising edge to the first
conductance plateau, explained by singlet and triplet resonances of conducting
electrons with a single weakly bound electron in the wire [T. Rejec, A. Ramsak,
and J.H. Jefferson, Phys. Rev. B 62, 12985 (2000)]. We extend this work to
study the Seebeck thermopower coefficient and linear thermal conductance within
the framework of the Landauer-Buettiker formalism, which also exhibit anomalous
structures. These features are generic and robust, surviving to temperatures of
a few degrees. It is shown quantitatively how at elevated temperatures thermal
conductance progressively deviates from the Wiedemann-Franz law.Comment: To appear in Phys. Rev. B 2002; 3 figure
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