250 research outputs found
Universal Scaling in Non-equilibrium Transport Through a Single-Channel Kondo Dot
Scaling laws and universality play an important role in our understanding of
critical phenomena and the Kondo effect. Here we present measurements of
non-equilibrium transport through a single-channel Kondo quantum dot at low
temperature and bias. We find that the low-energy Kondo conductance is
consistent with universality between temperature and bias and characterized by
a quadratic scaling exponent, as expected for the spin-1/2 Kondo effect. The
non-equilibrium Kondo transport measurements are well-described by a universal
scaling function with two scaling parameters.Comment: v2: improved introduction and theory-experiment comparsio
Experimental Realization of a Quantum Spin Pump
We demonstrate the operation of a quantum spin pump based on cyclic
radio-frequency excitation of a GaAs quantum dot, including the ability to pump
pure spin without pumping charge. The device takes advantage of bidirectional
mesoscopic fluctuations of pumped current, made spin-dependent by the
application of an in-plane Zeeman field. Spin currents are measured by placing
the pump in a focusing geometry with a spin-selective collector.Comment: related papers available at http://marcuslab.harvard.ed
Detecting Spin-Polarized Currents in Ballistic Nanostructures
We demonstrate a mesoscopic spin polarizer/analyzer system that allows the
spin polarization of current from a quantum point contact in an in-plane
magnetic field to be measured. A transverse focusing geometry is used to couple
current from an emitter point contact into a collector point contact. At large
in-plane fields, with the point contacts biased to transmit only a single spin
(g < e^2/h), the voltage across the collector depends on the spin polarization
of the current incident on it. Spin polarizations of greater than 80% are found
for both emitter and collector at 300mK and 7T in-plane field.Comment: related papers at http://marcuslab.harvard.ed
Imaging transverse electron focusing in semiconducting heterostructures with spin-orbit coupling
Transverse electron focusing in two-dimensional electron gases (2DEGs) with
strong spin-orbit coupling is revisited. The transverse focusing is related to
the transmission between two contacts at the edge of a 2DEG when a
perpendicular magnetic field is applied. Scanning probe microscopy imaging
techniques can be used to study the electron flow in these systems. Using
numerical techniques we simulate the images that could be obtained in such
experiments. We show that hybrid edge states can be imaged and that the
outgoing flux can be polarized if the microscope tip probe is placed in
specific positions.Comment: Contribution to the Book/Proceedings of the PITP Les Houches School
on "Quantum Magnetism" held on June, 2006. Final forma
Exascale Deep Learning to Accelerate Cancer Research
Deep learning, through the use of neural networks, has demonstrated
remarkable ability to automate many routine tasks when presented with
sufficient data for training. The neural network architecture (e.g. number of
layers, types of layers, connections between layers, etc.) plays a critical
role in determining what, if anything, the neural network is able to learn from
the training data. The trend for neural network architectures, especially those
trained on ImageNet, has been to grow ever deeper and more complex. The result
has been ever increasing accuracy on benchmark datasets with the cost of
increased computational demands. In this paper we demonstrate that neural
network architectures can be automatically generated, tailored for a specific
application, with dual objectives: accuracy of prediction and speed of
prediction. Using MENNDL--an HPC-enabled software stack for neural architecture
search--we generate a neural network with comparable accuracy to
state-of-the-art networks on a cancer pathology dataset that is also
faster at inference. The speedup in inference is necessary because of the
volume and velocity of cancer pathology data; specifically, the previous
state-of-the-art networks are too slow for individual researchers without
access to HPC systems to keep pace with the rate of data generation. Our new
model enables researchers with modest computational resources to analyze newly
generated data faster than it is collected.Comment: Submitted to IEEE Big Dat
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