1,895 research outputs found
Electron Spin Resonance at the Level of 10000 Spins Using Low Impedance Superconducting Resonators
We report on electron spin resonance (ESR) measurements of phosphorus donors
localized in a 200 square micron area below the inductive wire of a lumped
element superconducting resonator. By combining quantum limited parametric
amplification with a low impedance microwave resonator design we are able to
detect around 20000 spins with a signal-to-noise ratio (SNR) of 1 in a single
shot. The 150 Hz coupling strength between the resonator field and individual
spins is significantly larger than the 1 - 10 Hz coupling rates obtained with
typical coplanar waveguide resonator designs. Due to the larger coupling rate,
we find that spin relaxation is dominated by radiative decay into the resonator
and dependent upon the spin-resonator detuning, as predicted by Purcell
Effect of Exchange Interaction on Spin Dephasing in a Double Quantum Dot
We measure singlet-triplet dephasing in a two-electron double quantum dot in
the presence of an exchange interaction which can be electrically tuned from
much smaller to much larger than the hyperfine energy. Saturation of dephasing
and damped oscillations of the spin correlator as a function of time are
observed when the two interaction strengths are comparable. Both features of
the data are compared with predictions from a quasistatic model of the
hyperfine field.Comment: see related papers at http://marcuslab.harvard.ed
Manipulation of a single charge in a double quantum dot
We manipulate a single electron in a fully tunable double quantum dot using
microwave excitation. Under resonant conditions, microwaves drive transitions
between the (1,0) and (0,1) charge states of the double dot. Local quantum
point contact charge detectors enable a direct measurement of the
photon-induced change in occupancy of the charge states. From charge sensing
measurements, we find T1~16 ns and a lower bound estimate for T2* of 400 ps for
the charge two-level system.Comment: related articles at http://marcuslab.harvard.ed
Estudo histopatológico das lesões causadas pelo veneno de urutu (Bothrops alternatus) em músculo esquelético de camundongos
Veneno bruto de urutu (Bothrops alternatus) dissolvido em solução salina fisiológica foi injetado no músculo tibial anterior direito de camundongos adultos na dose de 80 μg. Os músculos foram examinados em cortes de parafina, corados por Hematoxilina e Eosina. Aos 10 minutos já havia intensa hemorragia difusa no M. tibial anterior, mas apenas raras fibras musculares estavam necróticas. Nas horas seguintes, contudo, observou-se rápido aumento do número de fibras afetadas, sendo que à s 24 hs o músculo apresentava-se totalmente necrótico. Vasos sangüÃneos intramusculares e nas proximidades do M. tibial anterior mostravam necrose hialina da camada média e por vezes trombose. A fagocitose dos restos celulares ocorreu da periferia para o centro e acompanhou-se de regeneração muscular. Após 1 a 2 meses, em vários animais houve recuperação considerável do músculo, embora com persistência de cicatriz. As fibras regeneradas possuiam núcleos centrais e variavam em diâmetro, estando muitas atróficas. Em outros camundongos a regeneração do M. tibial anterior foi muito precária, tendo este sido substituÃdo por tecido fibroadiposo com apenas raras fibras musculares. Os resultados mostram que, apesar da gravidade das lesões iniciais devidas ao veneno, ocorre regeneração muscular em grau variável de animal para animal. Sugere-se que a má regeneração observada em alguns casos poderia ser devida, ao menos em parte, a dano vascular permanente.Venom of urutu snake (Bothrops alternatus) injected into the Tibialis anterior muscle (Tib. ant.) of mice in a dose of 80 μg induced massive local haemorrhage within 10 min. Though muscle fibres appeared normal at this stage they later suffered necrosis in increasing numbers so that by 24 hr the whole muscle was necrotic. Arteries near the injection site often showed hyaline necrosis of the media and some were thrombosed. Phagocytosis of debris, which progressed from the periphery towards the centre of the necrotic area was usually complete by 2 weeks and was accompanied by muscle fibre regeneration. After 1 or 2 months several animals showed extensive recovery of the damaged muscle though a localized scar often remained. The regenerated muscle fibres showed central nuclei and varied in diameter, many appearing atrophic. In other mice, however, there was replacement of Tib. ant. by fibroadipose tissue with little or no muscle fibre regeneration. The results show that despite severe initial haemorrhage and necrosis, the affected muscles exhibit considerable capacity for regeneration. It is suggested that the poor regenerative response observed in some animals could result, at least to some extent, from permanent damage to the local blood vessels
Nonadiabatic quantum control of a semiconductor charge qubit
We demonstrate multipulse quantum control of a single electron charge qubit.
The qubit is manipulated by applying nonadiabatic voltage pulses to a surface
depletion gate and readout is achieved using a quantum point contact charge
sensor. We observe Ramsey fringes in the excited state occupation in response
to a pi/2 - pi/2 pulse sequence and extract T2* ~ 60 ps away from the charge
degeneracy point. Simulations suggest these results may be extended to
implement a charge-echo by reducing the interdot tunnel coupling and pulse rise
time, thereby increasing the nonadiabaticity of the pulses.Comment: Related papers at http://pettagroup.princeton.ed
Measurement of Temporal Correlations of the Overhauser Field in a Double Quantum Dot
In quantum dots made from materials with nonzero nuclear spins, hyperfine
coupling creates a fluctuating effective Zeeman field (Overhauser field) felt
by electrons, which can be a dominant source of spin qubit decoherence. We
characterize the spectral properties of the fluctuating Overhauser field in a
GaAs double quantum dot by measuring correlation functions and power spectra of
the rate of singlet-triplet mixing of two separated electrons. Away from zero
field, spectral weight is concentrated below 10 Hz, with 1/f^2 dependence on
frequency, f. This is consistent with a model of nuclear spin diffusion, and
indicates that decoherence can be largely suppressed by echo techniques.Comment: related papers available at http://marcuslab.harvard.ed
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