46 research outputs found
Universal decay cascade model for dynamic quantum dot initialization
Dynamic quantum dots can be formed by time-dependent electrostatic potentials
in nanoelectronic devices, such as gate- or surface-acoustic-wave-driven
electron pumps. Ability to control the number of captured electrons with high
precision is required for applications in fundamental metrology and quantum
information processing. In this work we propose and quantify a scheme to
initialize quantum dots with a controllable number of electrons. It is based on
the stochastic decrease in the electron number of a shrinking dynamic quantum
dot and is described by a nuclear decay cascade model with "isotopes" being
different charge states of the dot. Unlike the natural nuclei, the artificial
confinement is time-dependent and tunable, so the probability distribution for
the final "stable isotopes" depends on the external gate voltage. We derive an
explicit fitting formula to extract the sequence of decay rate ratios from the
measurements of averaged current in a periodically driven device. This provides
a device-specific fingerprint which allows to compare different devices and
architectures, and predict the upper limits of initialization accuracy from low
precision measurements.Comment: 4 pages; more general derivation, new figure on
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
Controlling the error mechanism in a tunable-barrier non-adiabatic charge pump by dynamic gate compensation
Single-electron pumps based on tunable-barrier quantum dots are the most
promising candidates for a direct realization of the unit ampere in the
recently revised SI: they are simple to operate and show high precision at high
operation frequencies. The current understanding of the residual transfer
errors at low temperature is based on the evaluation of backtunneling effects
in the decay cascade model. This model predicts a strong dependence on the
ratio of the time dependent changes in the quantum dot energy and the tunneling
barrier transparency. Here we employ a two-gate operation scheme to verify this
prediction and to demonstrate control of the backtunneling error. We derive and
experimentally verify a quantitative prediction for the error suppression,
thereby confirming the basic assumptions of the backtunneling (decay cascade)
model. Furthermore, we demonstrate a controlled transition from the
backtunneling dominated regime into the thermal (sudden decoupling) error
regime. The suppression of transfer errors by several orders of magnitude at
zero magnetic field was additionally verified by a sub-ppm precision
measurement