19,849 research outputs found
The Electronic States of Two Oppositely doped Mott Insulators Bilayers
We study the effect of Coulomb interaction between two oppositely doped
low-dimensional tJ model systems. We exactly show that, in the one-dimensional
case, an arbitrarily weak interaction leads to the formation of charge neutral
electron-hole pairs. We then use two different mean-field theories to address
the two-dimensional case, where inter-layer excitons also form and condense. We
propose that this results in new features which have no analog in single
layers, such as the emergence of an insulating spin liquid phase. Our simple
bilayer model might have relevance to the physics of doped Mott insulator
interfaces and of the new four layer Ba2CaCu4O8 compound.Comment: 4 pages, 1 figur
Tunneling spectra of layered strongly correlated d-wave superconductors
Tunneling conductance experiments on cuprate superconductors exhibit a large
diversity of spectra that appear in different nano-sized regions of
inhomogeneous samples. In this letter, we use a mean-field approach to the
tt't''J model in order to address the features in these spectra that deviate
from the BCS paradigm, namely, the bias sign asymmetry at high bias, the
generic lack of evidence for the Van Hove singularity, and the occasional
absence of coherence peaks. We conclude that these features can be reproduced
in homogeneous layered d-wave superconductors solely due to a proximate Mott
insulating transition. We also establish the connection between the above
tunneling spectral features and the strong renormalization of the electron
dispersion around (0,pi) and (pi,0) and the momentum space anisotropy of
electronic states observed in ARPES experiments.Comment: 4 pages, 3 figures. Added comment on the role of sample
inhomogeneity. Published version. Homepage http://dao.mit.edu/~wen
Control of conditional pattern with polarization entanglement
Conditional interference patterns can be obtained with twin photons from
spontaneous parametric down-conversion and the phase of the pattern can be
controlled by the relative transverse position of the signal and idler
detectors. Using a configuration that produces entangled photons in both
polarization and transverse momentum we report on the control of the
conditional patterns by acting on the polarization degree of freedom.Comment: Submitted for publication in Optics Communication
Nuclear State Preparation via Landau-Zener-Stueckelberg transitions in Double Quantum Dots
We theoretically model a nuclear-state preparation scheme that increases the
coherence time of a two-spin qubit in a double quantum dot. The two-electron
system is tuned repeatedly across a singlet-triplet level-anticrossing with
alternating slow and rapid sweeps of an external bias voltage. Using a
Landau-Zener-Stueckelberg model, we find that in addition to a small nuclear
polarization that weakly affects the electron spin coherence, the slow sweeps
are only partially adiabatic and lead to a weak nuclear spin measurement and a
nuclear-state narrowing which prolongs the electron spin coherence. This
resolves some open problems brought up by a recent experiment [D. J. Reilly et
al., Science 321, 817 (2008).]. Based on our description of the weak
measurement, we simulate a system with up to n=200 nuclear spins per dot.
Scaling in n indicates a stronger effect for larger n.Comment: 4.1 pages, 2 figure
Fast gates for ion traps by splitting laser pulses
We present a fast phase gate scheme that is experimentally achievable and has an operation time more than two orders of magnitude faster than current experimental schemes for low numbers of pulses. The gate time improves with the number of pulses following an inverse power law. Unlike
implemented schemes which excite precise motional sidebands, thus limiting
the gate timescale, our scheme excites multiple motional states using discrete
ultra-fast pulses.We use beam-splitters to divide pulses into smaller components
to overcome limitations due to the finite laser pulse repetition rate. This provides
gate times faster than proposed theoretical schemes when we optimize a practical
setup
Produção de mudas de goiabeira.
A goiaba ocupa lugar de destaque dentre as frutas tropicais brasileiras. No Vale do São Francisco, a área plantada com a cultura é de 5.000 hectares, distribuídos entre os estados de Pernambuco e Bahia. A goiaba é uma ótima opção para a diversificação, entretanto, com os problemas surgidos por causa do nematoide, muitos pomares foram erradicados. Visando contribuir para a redução desses problemas, deve-se dar importância especial à produção de mudas livres de nematoides, pois, é no preparo delas que grande parte das áreas são contaminadas por essa praga. A produção de mudas é uma das etapas fundamentais no processo de implantação de um pomar e pode ser determinante para o sucesso da cultura a ser implantada. As técnicas de produção devem atender às necessidades do produtor, levando-se em consideração a disponibilidade e a localização de áreas, o grau de tecnologia e os recursos financeiros disponíveis.bitstream/item/54791/1/COT148.pd
Biorreatores: aspectos gerais e sua utilização para cultura de tecidos vegetais.
Cultura de Tecidos Vegetais; Biorreatores na cultura de tecidos vegetais; Vantagens do uso de biorreatores em relação ao processo de micropropagação convencional; Problemas no uso de biorreatores e como contorná-los; Principais tipos de biorreatores; Principais parâmetros físicoquímicos em um biorreator; Formas e efeitos da agitação; Formas de transferência e efeitos do oxigênio dissolvido; Efeitos provocados pelas variações de CO2 e pH.bitstream/CPATSA-2009-09/40172/1/SDC214.pd
Coherent Adiabatic Spin Control in the Presence of Charge Noise Using Tailored Pulses
We study finite-time Landau-Zener transitions at a singlet-triplet level
crossing in a GaAs double quantum dot, both experimentally and theoretically.
Sweeps across the anticrossing in the high driving speed limit result in
oscillations with a small visibility. Here we demonstrate how to increase the
oscillation visibility while keeping sweep times shorter than T2* using a
tailored pulse with a detuning dependent level velocity. Our results show an
improvement of a factor ~2.9 for the oscillation visibility. In particular, we
were able to obtain a visibility of ~0.5 for St\"uckelberg oscillations, which
demonstrates the creation of an equally weighted superposition of the qubit
states.Comment: Related papers at http://pettagroup.princeton.ed
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