744,854 research outputs found
Fabrication and Characterization of Electrostatic Quantum Dots in a Si/SiGe 2D Electron Gas, Including an Integrated Read-out Channel
A new fabrication technique is used to produce quantum dots with read-out
channels in silicon/silicon-germanium two-dimensional electron gases. The
technique utilizes Schottky gates, placed on the sides of a shallow etched
quantum dot, to control the electronic transport process. An adjacent quantum
point contact gate is integrated to the side gates to define a read-out channel
and thus allow for noninvasive detection of the electronic occupation of the
quantum dot. Reproducible and stable Coulomb oscillations and the corresponding
jumps in the read-out channel resistance are observed at low temperatures. The
fabricated dot combined with the read-out channel represent a step towards the
spin-based quantum bit in Si/SiGe heterostructures.Comment: 3 pages, 4 fig
Increasing Flash Memory Lifetime by Dynamic Voltage Allocation for Constant Mutual Information
The read channel in Flash memory systems degrades over time because the
Fowler-Nordheim tunneling used to apply charge to the floating gate eventually
compromises the integrity of the cell because of tunnel oxide degradation.
While degradation is commonly measured in the number of program/erase cycles
experienced by a cell, the degradation is proportional to the number of
electrons forced into the floating gate and later released by the erasing
process. By managing the amount of charge written to the floating gate to
maintain a constant read-channel mutual information, Flash lifetime can be
extended. This paper proposes an overall system approach based on information
theory to extend the lifetime of a flash memory device. Using the instantaneous
storage capacity of a noisy flash memory channel, our approach allocates the
read voltage of flash cell dynamically as it wears out gradually over time. A
practical estimation of the instantaneous capacity is also proposed based on
soft information via multiple reads of the memory cells.Comment: 5 pages. 5 figure
On Termination for Faulty Channel Machines
A channel machine consists of a finite controller together with several fifo
channels; the controller can read messages from the head of a channel and write
messages to the tail of a channel. In this paper, we focus on channel machines
with insertion errors, i.e., machines in whose channels messages can
spontaneously appear. Such devices have been previously introduced in the study
of Metric Temporal Logic. We consider the termination problem: are all the
computations of a given insertion channel machine finite? We show that this
problem has non-elementary, yet primitive recursive complexity
Two-dimensional coding for probe recording on magnetic patterned media
The effect of intertrack intersymbol interference in a magnetic patterned medium is studied. A two-dimensional (2-D) channel code is proposed, dedicated to perpendicularly magnetized media without soft underlayer, which exhibit read pulses showing overshoot. Read pulse shapes were investigated using a magnetic-force microscope tip scanning the patterned medium row-by-row. To test different codes, a bit-detection simulation program was developed to generate large amounts of data on which bit error rates can be measured. Application of the 2-D channel code, which implies recording of particular dot positions with fixed bits ("ones", "zeros"), resulted in the elimination of 2-D worst-case bit patterns and a subsequent reduction of detected-bit errors. The accompanying redundancy of 22% is inevitable for this type of 2-D code
Multi-channel Kondo Models in non-Abelian Quantum Hall Droplets
We study the coupling between a quantum dot and the edge of a non-Abelian
fractional quantum Hall state which is spatially separated from it by an
integer quantum Hall state. Near a resonance, the physics at energy scales
below the level spacing of the edge states of the dot is governed by a
-channel Kondo model when the quantum Hall state is a Read-Rezayi state at
filling fraction or its particle-hole conjugate at
. The -channel Kondo model is channel isotropic even without
fine tuning in the former state; in the latter, it is generically channel
anisotropic. In the special case of , our results provide a new venue,
realized in a mesoscopic context, to distinguish between the Pfaffian and
anti-Pfaffian states at filling fraction .Comment: 4 pages, 1 figure; references updated, version to appear in PR
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