179 research outputs found
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
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
Identificação de cutans em perfis de latossol roxo e terra roxa estruturada
O presente trabalho teve por finalidade o estudo de cutans em dois perfis de solos pertencentes ao grande grupo Latossol Roxo (série Iracema, Município de Piracicaba, SP), e em dois perfis do grande grupo Terra Roxa Estruturada (Município de Botucatu, SP). Tal estudo baseou-se no exame das amostras dos perfis, em secções delgadas examinadas sob microscópio petrográfico. A análise de uma boa quantidade de lâminas revelou a presença de cutans iluviais nos horizantes B21 dos Lotossóis Roxos, no horizonte B1 e parte do B21 do perfil P3 (Terra Roxa Estruturada) e nos horizontes B21 e B22 do perfil P4 (Terra Roxa Estruturada).The purpose of this work was the study of cutans in two soil profiles of the Iracema series, Latossol Roxo Great Group, and two profiles of Terra Roxa Estruturada.] The study was based on the exam, under the petrographic microscope, of thin sections prepared from undisturbed soil samples taken from the main horizons of the four profiles under study. The exam of the thin sections revealed the presence of illuvial cutans in the B21 horizons of the Latossol Roxo (profiles P1 and P2), in the B1 and part of the B21 horizons of profile P3 (Terra Roxa Estruturada) and int the B21 and B22 horizons of profile P4 (Terra Roxa Estruturada)
Toy models of crossed Andreev reflection
We propose toy models of crossed Andreev reflection in multiterminal hybrid
structures containing out-of-equilibrium conductors. We apply the description
to two possible experiments: (i) to a device containing a large quantum dot
inserted in a crossed Andreev reflection circuit. (ii) To a device containing
an Aharonov-Bohm loop inserted in a crossed Andreev reflection circuit.Comment: 5 pages, 9 figures, minor modification
Secções delgadas de solos: método de impregnação
A method is described for impregnation undisturbed soil and clay materials with a clear and transparent plastic which polimerizes and hardens at room temperature. The impregnation is carried out under vacuum in a desiccator adapted to receive the impregnating solution (poliester resin Polylite T 213 and monomeric styrene, with methyl-ethyl-ketone peroxide as catalist). Thin sections of soil and clay materials were obtained with satisfactory results. The effectiveness of the impregnation was ascertained by the absence of sample desintegration, dissolution in water and cracking.O presente trabalho apresenta um método desenvolvido para a impregnação de amostras de solo indeformadas, com a posterior finalidade da confecção de secções delgadas. A impregnação é efetuada sob vácuo e em um dessecador adaptado para receber a mistura impregnante. Esta, é constituída pela resina poliéster Polylite T 213 diluída em monômero de estireno e catalisada com peróxido de metil-etil-cetona. A confecção das secções delgadas não apresentou problemas que pudessem ser atribuídos a falhas na impregnação, tais como desintegração da amostra, dissolução da mesma em água, trincas, etc. Lâminas de solos e argilas foram obtidas com resultados amplamente satisfatórios
Mesoscopic Coulomb Blockade in One-channel Quantum Dots
Signatures of "mesoscopic Coulomb blockade" are reported for quantum dots
with one fully transmitting point-contact lead, T1 = 1, T2 << 1. Unlike Coulomb
blockade (CB) in weak-tunneling devices (T1, T2 << 1), one-channel CB is a
mesoscopic effect requiring quantum coherence. Several distinctive features of
mesoscopic CB are observed, including a reduction in CB upon breaking
time-reversal symmetry with a magnetic field, relatively large fluctuations of
peak position as a function of magnetic field, and strong temperature
dependence on the scale of the quantum level spacing.Comment: 12 pages, including 4 figure
Robustness of adiabatic passage trough a quantum phase transition
We analyze the crossing of a quantum critical point based on exact results
for the transverse XY model. In dependence of the change rate of the driving
field, the evolution of the ground state is studied while the transverse
magnetic field is tuned through the critical point with a linear ramping. The
excitation probability is obtained exactly and is compared to previous studies
and to the Landau-Zener formula, a long time solution for non-adiabatic
transitions in two-level systems. The exact time dependence of the excitations
density in the system allows to identify the adiabatic and diabatic regions
during the sweep and to study the mesoscopic fluctuations of the excitations.
The effect of white noise is investigated, where the critical point transmutes
into a non-hermitian ``degenerate region''. Besides an overall increase of the
excitations during and at the end of the sweep, the most destructive effect of
the noise is the decay of the state purity that is enhanced by the passage
through the degenerate region.Comment: 16 pages, 15 figure
Relation between Barrier Conductance and Coulomb Blockade Peak Splitting for Tunnel-Coupled Quantum Dots
We study the relation between the barrier conductance and the Coulomb
blockade peak splitting for two electrostatically equivalent dots connected by
tunneling channels with bandwidths much larger than the dot charging energies.
We note that this problem is equivalent to a well-known single-dot problem and
present solutions for the relation between peak splitting and barrier
conductance in both the weak and strong coupling limits. Results are in good
qualitative agreement with the experimental findings of F. R. Waugh et al.Comment: 19 pages (REVTeX 3.0), 3 Postscript figure
Strong Tunneling and Coulomb Blockade in a Single-Electron Transistor
We have developed a detailed experimental study of a single-electron
transistor in a strong tunneling regime. Although weakened by strong charge
fluctuations, Coulomb effects were found to persist in all samples including
one with the effective conductance 8 times higher than the quantum value (6.45
k). A good agreement between our experimental data and
theoretical results for the strong tunneling limit is found. A reliable
operation of transistors with conductances 3-4 times larger than the quantum
value is demonstrated.Comment: revtex, 4 page
Fluctuation Dominated Josephson Tunneling with a Scanning Tunneling Microscope
We demonstrate Josephson tunneling in vacuum tunnel junctions formed between
a superconducting scanning tunneling microscope tip and a Pb film, for junction
resistances in the range 50-300 k. We show that the superconducting
phase dynamics is dominated by thermal fluctuations, and that the Josephson
current appears as a peak centered at small finite voltages. In the presence of
microwave fields (f=15.0 GHz) the peak decreases in magnitude and shifts to
higher voltages with increasing rf power, in agreement with theory.Comment: 4 pages, REVTeX, submitted to PR
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