97 research outputs found
Parity Effect in a Small Superconducting Particle
Matveev and Larkin calculated the parity effect on the ground state energy of
a small superconducting particle in the regimes where the mean level spacing is
either large or small compared to the bulk gap. We perform a numerical
calculation which extends their results into the intermediate regime, where the
level spacing is of the same order as the bulk gap.Comment: 6 LaTeX pages, including 2 EPS figures; corrected reference and
spellin
Effects of low-frequency noise cross-correlations in coupled superconducting qubits
We study the effects of correlated low frequency noise sources acting on a
two qubit gate in a fixed coupling scheme. A phenomenological model for the
spatial and cross-talk correlations is introduced. The decoherence inside the
SWAP subspace is analysed by combining analytic results based on the adiabatic
approximation and numerical simulations. Results critically depend on amplitude
of the low frequency noise with respect to the qubits coupling strength.
Correlations between noise sources induce qualitative different behaviors
depending on the values of the above parameters. The possibility to reduce
dephasing due to correlated low frequency noise by a recalibration protocol is
discussed.Comment: 18 pages, 7 figure
Broadband noise decoherence in solid-state complex architectures
Broadband noise represents a severe limitation towards the implementation of
a solid-state quantum information processor. Considering common spectral forms,
we propose a classification of noise sources based on the effects produced
instead of on their microscopic origin. We illustrate a multi-stage approach to
broadband noise which systematically includes only the relevant information on
the environment, out of the huge parametrization needed for a microscopic
description. We apply this technique to a solid-state two-qubit gate in a fixed
coupling implementation scheme.Comment: Proceedings of Nobel Symposium 141: Qubits for Future Quantum
Informatio
Dynamical suppression of telegraph and 1/f noise due to quantum bistable fluctuator
We study dynamical decoupling of a qubit from non gaussian quantum noise due
to discrete sources, as bistable fluctuators and 1/f noise. We obtain analytic
and numerical results for generic operating point. For very large pulse
frequency, where dynamic decoupling compensates decoherence, we found universal
behavior. At intermediate frequencies noise can be compensated or enhanced,
depending on the nature of the fluctuators and on the operating point. Our
technique can be applied to a larger class of non-gaussian environments.Comment: Revtex 4, 5 pages, 3 figures. Title revised and some other minor
changed. Final version as published in PR
Interplay between pairing and exchange in small metallic dots
We study the effects of the mesoscopic fluctuations on the competition
between exchange and pairing interactions in ultrasmall metallic dots when the
mean level spacing is comparable or larger than the BCS pairing energy. Due to
mesoscopic fluctuations, the probability to have a non-zero spin ground state
may be non-vanishing and shows universal features related to both level
statistics and interaction. Sample to sample fluctuations of the renormalized
pairing are enlightened.Comment: 10 pages, 5 figure
Fixed-N Superconductivity: The Crossover from the Bulk to the Few-Electron Limit
We present a truly canonical theory of superconductivity in ultrasmall
metallic grains by variationally optimizing fixed-N projected BCS
wave-functions, which yields the first full description of the entire crossover
from the bulk BCS regime (mean level spacing bulk gap )
to the ``fluctuation-dominated'' few-electron regime (). A
wave-function analysis shows in detail how the BCS limit is recovered for , and how for pairing correlations become
delocalized in energy space. An earlier grand-canonical prediction for an
observable parity effect in the spectral gaps is found to survive the fixed-N
projection.Comment: 4 pages, 3 figures, RevTeX, V2: minor charges to mach final printed
versio
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