1,306 research outputs found
Realization of an Inductance Scale Traceable to the Quantum Hall Effect Using an Automated Synchronous Sampling System
In this paper, the realization of an inductance scale from 1~H to 10~H
for frequencies ranging between 50~Hz to 20~kHz is presented. The scale is
realized directly from a series of resistance standards using a fully automated
synchronous sampling system. A careful systematic characterization of the
system shows that the lowest uncertainties, around 12~H/H, are obtained
for inductances in the range from 10~mH to 100~mH at frequencies in the kHz
range. This new measurement system which was successfully evaluated during an
international comparison, provides a primary realization of the henry, directly
traceable to the quantum Hall effect. An additional key feature of this system
is its versatility. In addition to resistance-inductance (R-L) comparison, any
kind of impedances can be compared: R-R, R-C, L-L or C-C, giving this sampling
system a great potential of use in many laboratories around the world
Single-electron current sources: towards a refined definition of ampere
Controlling electrons at the level of elementary charge has been
demonstrated experimentally already in the 1980's. Ever since, producing an
electrical current , or its integer multiple, at a drive frequency has
been in a focus of research for metrological purposes. In this review we first
discuss the generic physical phenomena and technical constraints that influence
charge transport. We then present the broad variety of proposed realizations.
Some of them have already proven experimentally to nearly fulfill the demanding
needs, in terms of transfer errors and transfer rate, of quantum metrology of
electrical quantities, whereas some others are currently "just" wild ideas,
still often potentially competitive if technical constraints can be lifted. We
also discuss the important issues of read-out of single-electron events and
potential error correction schemes based on them. Finally, we give an account
of the status of single-electron current sources in the bigger framework of
electric quantum standards and of the future international SI system of units,
and briefly discuss the applications and uses of single-electron devices
outside the metrological context.Comment: 55 pages, 38 figures; (v2) fixed typos and misformatted references,
reworded the section on AC pump
Superconducting Quantum Circuits, Qubits and Computing
This paper gives an introduction to the physics and principles of operation
of quantized superconducting electrical circuits for quantum information
processing.Comment: 59 pages 68 figures. Prepared for Handbook of Theoretical and
Computational Nanotechnolog
QND measurement of a superconducting qubit in the weakly projective regime
Quantum state detectors based on switching of hysteretic Josephson junctions
biased close to their critical current are simple to use but have strong
back-action. We show that the back-action of a DC-switching detector can be
considerably reduced by limiting the switching voltage and using a fast
cryogenic amplifier, such that a single readout can be completed within 25 ns
at a repetition rate of 1 MHz without loss of contrast. Based on a sequence of
two successive readouts we show that the measurement has a clear quantum
non-demolition character, with a QND fidelity of 75 %.Comment: submitted to PR
Topological Superconductivity in a Phase-Controlled Josephson Junction
Topological superconductors can support localized Majorana states at their
boundaries. These quasi-particle excitations have non-Abelian statistics that
can be used to encode and manipulate quantum information in a topologically
protected manner. While signatures of Majorana bound states have been observed
in one-dimensional systems, there is an ongoing effort to find alternative
platforms that do not require fine-tuning of parameters and can be easily
scalable to large numbers of states. Here we present a novel experimental
approach towards a two-dimensional architecture. Using a Josephson junction
made of HgTe quantum well coupled to thin-film aluminum, we are able to tune
between a trivial and a topological superconducting state by controlling the
phase difference across the junction and applying an in-plane magnetic
field. We determine the topological state of the induced superconductor by
measuring the tunneling conductance at the edge of the junction. At low
magnetic fields, we observe a minimum in the tunneling spectra near zero bias,
consistent with a trivial superconductor. However, as the magnetic field
increases, the tunneling conductance develops a zero-bias peak which persists
over a range of that expands systematically with increasing magnetic
fields. Our observations are consistent with theoretical predictions for this
system and with full quantum mechanical numerical simulations performed on
model systems with similar dimensions and parameters. Our work establishes this
system as a promising platform for realizing topological superconductivity and
for creating and manipulating Majorana modes and will therefore open new
avenues for probing topological superconducting phases in two-dimensional
systems.Comment: Supplementary contains resized figures. Original files are available
upon reques
Quantum Metrology Triangle Experiments: A Status Review
Quantum Metrology Triangle experiments combine three quantum electrical
effects (the Josephson effect, the quantum Hall effect and the single-electron
transport effect) used in metrology. These experiments allow important
fundamental consistency tests on the validity of commonly assumed relations
between fundamental constants of nature and the quantum electrical effects.
This paper reviews the history, results and the present status and perspectives
of Quantum Metrology Triangle experiments. It also reflects on the possible
implications of results for the knowledge on fundamental constants and the
quantum electrical effects.Comment: 36 pages, 8 figure
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