947 research outputs found
Towards single-electron metrology
We review the status of the understanding of single-electron transport (SET)
devices with respect to their applicability in metrology. Their envisioned role
as the basis of a high-precision electrical standard is outlined and is
discussed in the context of other standards. The operation principles of single
electron transistors, turnstiles and pumps are explained and the fundamental
limits of these devices are discussed in detail. We describe the various
physical mechanisms that influence the device uncertainty and review the
analytical and numerical methods needed to calculate the intrinsic uncertainty
and to optimise the fabrication and operation parameters. Recent experimental
results are evaluated and compared with theoretical predictions. Although there
are discrepancies between theory and experiments, the intrinsic uncertainty is
already small enough to start preparing for the first SET-based metrological
applications.Comment: 39 pages, 14 figures. Review paper to be published in International
Journal of Modern Physics
Practical quantum realization of the ampere from the electron charge
One major change of the future revision of the International System of Units
(SI) is a new definition of the ampere based on the elementary charge \emph{e}.
Replacing the former definition based on Amp\`ere's force law will allow one to
fully benefit from quantum physics to realize the ampere. However, a quantum
realization of the ampere from \emph{e}, accurate to within in
relative value and fulfilling traceability needs, is still missing despite many
efforts have been spent for the development of single-electron tunneling
devices. Starting again with Ohm's law, applied here in a quantum circuit
combining the quantum Hall resistance and Josephson voltage standards with a
superconducting cryogenic amplifier, we report on a practical and universal
programmable quantum current generator. We demonstrate that currents generated
in the milliampere range are quantized in terms of
( is the Josephson frequency) with a measurement uncertainty of
. This new quantum current source, able to deliver such accurate
currents down to the microampere range, can greatly improve the current
measurement traceability, as demonstrated with the calibrations of digital
ammeters. Beyond, it opens the way to further developments in metrology and in
fundamental physics, such as a quantum multimeter or new accurate comparisons
to single electron pumps.Comment: 15 pages, 4 figure
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
Novel methods of fabrication and metrology of superconducting nanostructures
As metrology extends toward the nanoscale, a number of potential applications and new challenges arise. By combining photolithography with focused ion beam and/or electron beam methods, superconducting quantum interference devices (SQUIDs) with loop dimensions down to 200 nm and superconducting bridge dimensions of the order 80 nm have been produced. These SQUIDs have a range of potential applications. As an illustration, we describe a method for characterizing the effective area and the magnetic penetration depth of a structured superconducting thin film in the extreme limit, where the superconducting penetration depth is much greater than the film thickness and is comparable with the lateral dimensions of the device
Automated Setup to Accurately Calibrate Electrical DC Voltage Generators
At National Institute of Metrological Research (INRIM), an automated setup to
calibrate DC Voltage generators, mainly top-level calibrators from 1 mV to 1 kV
has been developed. The heart of the setup is an INRIM-built automated fixed
ratios DC Voltage divider. The significant achievement of this setup is the
possibility to interconnect the divider, a DMM characterized in linearity, a DC
Voltage Standard and a DC Voltage generator under calibration and automatically
to manage the calibration process. This calibration method allows to save a lot
of time, to improve the reliability and to increase the accuracy of the
calibration of generators. The relative uncertainties of the system span from
0.6x10-6 to 1.2x10-4 improving the previous capabilities of the INRIM
laboratory for calibration of programmable multifunction instruments. In
addition, this system allows to avoid the employment of several Standards (some
of them still manually operating) carrying out the entire process without
changing the setup configuration and without the presence of operators. The
concept of this setup can be transferred to secondary high-level electrical
calibration Laboratories that could be consider it useful for their calibration
activities.Comment: 6 pages 8 figure
Coulomb blockade and Bloch oscillations in superconducting Ti nanowires
Quantum fluctuations in quasi-one-dimensional superconducting channels
leading to spontaneous changes of the phase of the order parameter by ,
alternatively called quantum phase slips (QPS), manifest themselves as the
finite resistance well below the critical temperature of thin superconducting
nanowires and the suppression of persistent currents in tiny superconducting
nanorings. Here we report the experimental evidence that in a current-biased
superconducting nanowire the same QPS process is responsible for the insulating
state -- the Coulomb blockade. When exposed to RF radiation, the internal Bloch
oscillations can be synchronized with the external RF drive leading to
formation of quantized current steps on the I-V characteristic. The effects
originate from the fundamental quantum duality of a Josephson junction and a
superconducting nanowire governed by QPS -- the QPS junction (QPSJ).Comment: 5 pages, 4 figure
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