55,480 research outputs found
Spin Qubits in Multi-Electron Quantum Dots
We study the effect of mesoscopic fluctuations on the magnitude of errors
that can occur in exchange operations on quantum dot spin-qubits. Mid-size
double quantum dots, with an odd number of electrons in the range of a few tens
in each dot, are investigated through the constant interaction model using
realistic parameters. It is found that the constraint of having short pulses
and small errors implies keeping accurate control, at the few percent level, of
several electrode voltages. In practice, the number of independent parameters
per dot that one should tune depends on the configuration and ranges from one
to four.Comment: RevTex, 6 pages, 5 figures. v3: two figures added, more details
provided. Accepted for publication in PR
Phonon Squeezed States Generated by Second Order Raman Scattering
We study squeezed states of phonons, which allow a reduction in the quantum
fluctuations of the atomic displacements to below the zero-point quantum noise
level of coherent phonon states. We investigate the generation of squeezed
phonon states using a second order Raman scattering process. We calculate the
expectation values and fluctuations of both the atomic displacement and the
lattice amplitude operators, as well as the effects of the phonon squeezed
states on macroscopically measurable quantities, such as changes in the
dielectric constant. These results are compared with recent experiments.Comment: 4 pages, REVTE
Comment on "Single-mode excited entangled coherent states"
In Xu and Kuang (\textit{J. Phys. A: Math. Gen.} 39 (2006) L191), the authors
claim that, for single-mode excited entangled coherent states , \textquotedblleft the photon excitations lead to the
decrease of the concurrence in the strong field regime of and
the concurrence tends to zero when ". This is wrong.Comment: 4 apges, 2 figures, submitted to JPA 15 April 200
The Universal Edge Physics in Fractional Quantum Hall Liquids
The chiral Luttinger liquid theory for fractional quantum Hall edge transport
predicts universal power-law behavior in the current-voltage (-)
characteristics for electrons tunneling into the edge. However, it has not been
unambiguously observed in experiments in two-dimensional electron gases based
on GaAs/GaAlAs heterostructures or quantum wells. One plausible cause is the
fractional quantum Hall edge reconstruction, which introduces non-chiral edge
modes. The coupling between counterpropagating edge modes can modify the
exponent of the - characteristics. By comparing the fractional
quantum Hall states in modulation-doped semiconductor devices and in graphene
devices, we show that the graphene-based systems have an experimental
accessible parameter region to avoid the edge reconstruction, which is suitable
for the exploration of the universal edge tunneling exponent predicted by the
chiral Luttinger liquid theory.Comment: 7 pages, 6 figure
Analytical Solution of Electron Spin Decoherence Through Hyperfine Interaction in a Quantum Dot
We analytically solve the {\it Non-Markovian} single electron spin dynamics
due to hyperfine interaction with surrounding nuclei in a quantum dot. We use
the equation-of-motion method assisted with a large field expansion, and find
that virtual nuclear spin flip-flops mediated by the electron contribute
significantly to a complete decoherence of transverse electron spin correlation
function. Our results show that a 90% nuclear polarization can enhance the
electron spin time by almost two orders of magnitude. In the long time
limit, the electron spin correlation function has a non-exponential
decay in the presence of both polarized and unpolarized nuclei.Comment: 4 pages, 3 figure
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