52 research outputs found
High-order cumulants in the counting statistics of asymmetric quantum dots
Measurements of single electron tunneling through a quantum dot using a
quantum point contact as charge detector have been performed for very long time
traces with very large event counts. This large statistical basis is used for a
detailed examination of the counting statistics for varying symmetry of the
quantum dot system. From the measured statistics we extract high order
cumulants describing the distribution. Oscillations of the high order cumulants
are observed when varying the symmetry. We compare this behavior to the
observed oscillation in time dependence and show that the variation of both
system variables lead to the same kind of oscillating response.Comment: 3 page
A self-referenced single-electron current source
[no abstract
Integrated quantized electronics: a semiconductor quantized voltage source
The Josephson effect in superconductors links a quantized output voltage Vout
= f \cdot(h/2e) to the natural constants of the electron's charge e, Planck's
constant h, and to an excitation frequency f with important applications in
electrical quantum metrology. Also semiconductors are routinely applied in
electrical quantum metrology making use of the quantum Hall effect. However,
despite their broad range of further applications e.g. in integrated circuits,
quantized voltage generation by a semiconductor device has never been obtained.
Here we report a semiconductor quantized voltage source generating quantized
voltages Vout = f\cdot(h/e). It is based on an integrated quantized circuit of
a single electron pump operated at pumping frequency f and a quantum Hall
device monolithically integrated in series. The output voltages of several \muV
are expected to be scalable by orders of magnitude using present technology.
The device might open a new route towards the closure of the quantum
metrological triangle. Furthermore it represents a universal electrical quantum
reference allowing to generate quantized values of the three most relevant
electrical units of voltage, current, and resistance based on fundamental
constants using a single device.Comment: 15 pages, 3 figure
A quantized current source with mesoscopic feedback
We study a mesoscopic circuit of two quantized current sources, realized by
non-adiabatic single- electron pumps connected in series with a small
micron-sized island in between. We find that quantum transport through the
second pump can be locked onto the quantized current of the first one by a
feedback due to charging of the mesoscopic island. This is confirmed by a
measurement of the charge variation on the island using a nearby charge
detector. Finally, the charge feedback signal clearly evidences loading into
excited states of the dynamic quantum dot during single-electron pump
operation
Prediction of warping in thermoplastic AFP-manufactured laminates through simulation and experimentation
The thermoplastic automated fibre placement (T-AFP) process is a non-autoclave method for in-situ consolidation of thermoplastic composite material on a piecewise constructed laminate. High thermal gradients and nonlinear material behaviour, especially due to crystallization, make predic-tions of process-induced stress and warping difficult. This paper describes a method for simulating parts manufactured by T-AFP using a detailed material model to capture the dynamic nature of the process. The material model is flexible and can be altered to describe different semi-crystalline matrices, in this study focusing on low-melt polyaryletherketone (LM-PAEK). Two laminate panels are simulated within this work and assess the impact of a heated tooling on overall part warping. Panel warping is validated by performing 3D-scans of T-AFP-manufactured laminates produced using the same parameters as the simulation. The results show a good match between numeric and experimental warping, especially for heated tools, thus providing a useful method for predict-ing laminate warping and reducing the demand on manufacturing experimentation
Aerogel Waveplates
Optical transmission measurements were made on 98% porosity silica aerogel
samples under various degrees of uniaxial strain. Uniaxially compressed
aerogels exhibit large birefringence, proportional to the amount of
compression, up to the 15% strain studied. The birefringence is mostly
reversible and reproducible through multiple compression-decompression cycles.
Our study demonstrates that uniaxially strained high porosity aerogels can be
used as tunable waveplates in a broad spectral range.Comment: 7 pages, 4 figures, submitted to Optics Expres
Addressable electron spin resonance using donors and donor molecules in silicos
Phosphorus donor impurities in silicon are a promising candidate for solid-state quantum computing due to their exceptionally long coherence times and high fidelities. However, individual addressability of exchange coupled donors with separations ~15 nm is challenging. We show that by using atomic precision lithography, we can place a single P donor next to a 2P molecule 16 ± 1 nm apart and use their distinctive hyperfine coupling strengths to address qubits at vastly different resonance frequencies. In particular, the single donor yields two hyperfine peaks separated by 97 ± 2.5 MHz, in contrast to the donor molecule that exhibits three peaks separated by 262 ± 10 MHz. Atomistic tight-binding simulations confirm the large hyperfine interaction strength in the 2P molecule with an interdonor separation of ~0.7 nm, consistent with lithographic scanning tunneling microscopy images of the 2P site during device fabrication. We discuss the viability of using donor molecules for built-in addressability of electron spin qubits in silicon
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