80 research outputs found
Electron-hole localization in coupled quantum dots
We theoretically investigate correlated electron-hole states in vertically
coupled quantum dots. Employing a prototypical double-dot confinement and a
configuration-interaction description for the electron-hole states, it is shown
that the few-particle ground state undergoes transitions between different
quantum states as a function of the interdot distance, resulting in unexpected
spatial correlations among carriers and in electron-hole localization. Such
transitions provide a direct manifestations of inter- and intradot
correlations, which can be directly monitored in experiments.Comment: 11 pages, 3 figures (eps), LaTeX 2e. To appear in PRB (Rapid
Communication
Universal quantum magnetometry with spin states at equilibrium
We address metrological protocols for the estimation of the intensity and the
orientation of a magnetic field, and show that quantum-enhanced precision may
be achieved by probing the field with an arbitrary spin at thermal equilibrium.
We derive a general expression for the ultimate achievable precision, as given
by the quantum Fisher information, and express this quantity in terms of common
thermodynamic quantities. We also seek for the optimal observable, and show
that it corresponds to the spin projection along a suitable direction, defined
by a universal function of the spin temperature. Finally, we prove the
robustness of our scheme against deviations of the measured spin projection
from optimality.Comment: Phys. Rev. Lett., in pres
Semiconductor quantum tubes: dielectric modulation and excitonic response
We study theoretically the optical properties of quantum tubes,
one-dimensional semiconductor nanostructures where electrons and holes are
confined to a cylindrical shell. In these structures, which bridge between 2D
and 1D systems, the electron-hole interaction may be modulated by a dielectric
substance outside the quantum tube and possibly inside its core. We use the
exact Green's function for the appropriate dielectric configuration and exact
diagonalization of the electron-hole interaction within an effective mass
description to predict the evolution of the exciton binding energy and
oscillator strength. Contrary to the homogeneous case, in dielectrically
modulated tubes the exciton binding is a function of the tube diameter and can
be tuned to a large extent by structure design and proper choice of the
dielectric media.Comment: 9 pages, 6 figures, in print for Phys. Rev.
Tunneling and Electric-Field Effects on Electron-Hole Localization in Artificial Molecules
We theoretically investigate the Stark shift of the exciton goundstate in two
vertically coupled quantum dots as a function of the interdot distance. The
coupling is shown to enhance the tuneability of the linear optical properties,
including energy and oscillator strength, as well as the exciton
polarizability. The coupling regime that maximizes these properties results
from the detailed balance between the effects of the single-particle tunneling,
of the electric field and of the carrier-carrier interaction. We discuss the
relevance of these results to the possible implementation of
quantum-information processing based on semiconductor quantum dots: in
particular, we suggest the identification of the qubits with the exciton levels
in coupled- rather than single-dots
Hyperfine-induced decoherence in triangular spin-cluster qubits
We investigate hyperfine-induced decoherence in a triangular spin-cluster for
different qubit encodings. Electrically controllable eigenstates of spin
chirality (C_z) show decoherence times that approach milliseconds, two orders
of magnitude longer than those estimated for the eigenstates of the total spin
projection (S_z) and of the partial spin sum (S_{12}). The robustness of
chirality is due to its decoupling from both the total- and individual-spin
components in the cluster. This results in a suppression of the effective
interaction between C_z and the nuclear spin bath
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