Reservoir computing is a recurrent machine learning framework that expands the dimensionality of a problem by mapping an input signal into a higher-dimension reservoir space that can capture and predict features of complex, nonlinear temporal dynamics. Here, we report on a bulk optical demonstration of an analog reservoir computer using speckles generated by propagating a laser beam modulated with a spatial light modulator through a multimode waveguide. We demonstrate that the hardware can successfully perform a multivariate audio classification task performed using the Japanese vowel speakers public data set. We perform full wave optical calculations of this architecture implemented in a chip-scale platform using an SiO2 waveguide and demonstrate that it performs as well as a fully numerical implementation of reservoir computing. As all the optical components used in the experiment can be fabricated using a commercial photonic integrated circuit foundry, our result demonstrates a framework for building a scalable, chip-scale, reservoir computer capable of performing optical signal processing.
Spin drag measurements were performed in a two-dimensional electron system set close to the crossed spin helix regime and coupled by strong intersubband scattering. In a sample with uncommon combination of long spin lifetime and high charge mobility, the drift transport allows us to determine the spin-orbit field and the spin mobility anisotropies. We used a random walk model to describe the system dynamics and found excellent agreement for the Rashba and Dresselhaus couplings. The proposed two-subband system displays a large tuning lever arm for the Rashba constant with gate voltage, which provides a new path towards a spin transistor. Furthermore, the data shows large spin mobility controlled by the spin-orbit constants setting the field along the direction perpendicular to the drift velocity. This work directly reveals the resistance experienced in the transport of a spin-polarized packet as a function of the strength of anisotropic spin-orbit fields.
Photoluminescence spectroscopy and Hanle effect measurements are used to
investigate carrier spin dephasing and recombination times in the semiconductor
alloy GaAsBi as a function of temperature and excitation energy. Hanle effect
measurements reveal the product of g-factor and effective spin dephasing time
(gTs) ranges from 0.8 ns at 40 K to 0.1 ns at 120 K. The temperature dependence
of gTs provides evidence for a thermally activated effect, which is attributed
to hole localization at single Bi or Bi cluster sites below 40 K.Comment: 5 pages, 3 figure
The current-induced spin polarization and momentum-dependent spin-orbit field were measured in In x Ga 1−x As epilayers with varying indium concentrations and silicon doping densities. Samples with higher indium concentrations and carrier concentrations and lower mobilities were found to have larger electrical spin generation efficiencies. Furthermore, current-induced spin polarization was detected in GaAs epilayers despite the absence of measurable spin-orbit fields, indicating that the extrinsic contributions to the spin polarization mechanism must be considered. Theoretical calculations based on a model that includes extrinsic contributions to the spin dephasing and the spin Hall effect, in addition to the intrinsic Rashba and Dresselhaus spin-orbit coupling, are found to qualitatively agree with the experimental results.
We report on the modification of the g-factor by an in-plane electric field in an In0.031Ga0.969As epilayer. We performed external magnetic field scans of the Kerr rotation of the InGaAs film in order to independently determine the g-factor and the spin-orbit fields. The g-factor increases from −0.4473 ± 0.0001 at 0 V/cm to −0.4419 ± 0.0001 at 25 V/cm applied along the [110] crystal axis. In addition, spatially-resolved spin measurements show a g-factor dependence on diffusive velocity. The change in g-factor with electric field can have a large effect on the determination of the internal spin-orbit and nuclear fields from Larmor precession frequency measurements.
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