47 research outputs found
Zwischen Anspruch und Realität: Evidenzbasierte Qualitätsentwicklung durch Integration von Qualitätsmanagement und Hochschuldidaktik
Eine evidenzbasierte Gestaltung von Studium und Lehre, wie sie heute normativ eingefordert wird, bedarf des integrierten Zusammenwirkens von Qualitätsmanagement und Hochschuldidaktik – aber gibt es dieses in der Praxis? Mit Blick auf die allgemeine Befundlage, aber auch anhand einer eigenen empirischen Untersuchung zeigt der Beitrag diesbezüglich auf, dass Qualitätsmanagement und Hochschuldidaktik als weitgehend desintegrierte Funktionsbereiche wahrgenommen werden und Evidenzbasierung in der Praxis folglich keinen sehr hohen Stellenwert genießt. Ausgehend von einer Ursachenanalyse wird auf die dysfunktionalen, aber auch auf die funktionalen Auswirkungen dieser Separierung aufmerksam gemacht
Qualitätsmanagement als Treiber einer evidenzbasierten Qualitätsentwicklung von Studium und Lehre?
Evidenzbasierte Qualitätsentwicklung von Studium und Lehre bedarf des Engagements von Hochschulleitungen und der Reflexionsbereitschaft von Lehrenden, aber vor allem auch der Unterstützung durch das hochschulische Qualitätsmanagement (QM). Ausgehend von einem Verständnis von QM als intermediärer Instanz zwischen Hochschuldidaktik und Lehrpraxis widmet sich der Beitrag daher der Frage, inwiefern QM auf diese Aufgabe vorbereitet ist. Anhand einer qualitativen und einer quantitativen Befragung von QM-Beschäftigten deutscher Hochschulen wird ein diesbezüglich eher skeptisches Bild gezeichnet. Statt einer Wissenschaftsorientierung scheinen vielmehr pragmatische Kalküle und damit einhergehende Zweckkonflikte die QM-Praxis zu dominieren
Decoherence in Josephson Qubits from Dielectric Loss
Dielectric loss from two-level states is shown to be a dominant decoherence
source in superconducting quantum bits. Depending on the qubit design,
dielectric loss from insulating materials or the tunnel junction can lead to
short coherence times. We show that a variety of microwave and qubit
measurements are well modeled by loss from resonant absorption of two-level
defects. Our results demonstrate that this loss can be significantly reduced by
using better dielectrics and fabricating junctions of small area . With a redesigned phase qubit employing low-loss
dielectrics, the energy relaxation rate has been improved by a factor of 20,
opening up the possibility of multi-qubit gates and algorithms.Comment: shortened version submitted to PR
Optical closure for an aerosol column: Method, accuracy, and inferable properties applied to a biomass-burning aerosol and its radiative forcing
The White Mountain Polarimeter Telescope and an Upper Limit on CMB Polarization
The White Mountain Polarimeter (WMPol) is a dedicated ground-based microwave
telescope and receiver system for observing polarization of the Cosmic
Microwave Background. WMPol is located at an altitude of 3880 meters on a
plateau in the White Mountains of Eastern California, USA, at the Barcroft
Facility of the University of California White Mountain Research Station.
Presented here is a description of the instrument and the data collected during
April through October 2004. We set an upper limit on -mode polarization of
14 (95% confidence limit) in the multipole range
. This result was obtained with 422 hours of observations of a 3
sky area about the North Celestial Pole, using a 42 GHz
polarimeter. This upper limit is consistent with polarization predicted
from a standard -CDM concordance model.Comment: 35 pages. 12 figures. To appear in ApJ
Quantum bits with Josephson junctions
Already in the first edition of this book (Barone and Paterno, "Fundamentals
and Physics and Applications of the Josephson Effect", Wiley 1982), a great
number of interesting and important applications for Josephson junctions were
discussed. In the decades that have passed since then, several new applications
have emerged. This chapter treats one such new class of applications: quantum
optics and quantum information processing (QIP) based on superconducting
circuits with Josephson junctions. In this chapter, we aim to explain the
basics of superconducting quantum circuits with Josephson junctions and
demonstrate how these systems open up new prospects, both for QIP and for the
study of quantum optics and atomic physics.Comment: 30 pages, 10 figures. Book chapter for a new edition of Barone and
Paterno's "Fundamentals and Physics and Applications of the Josephson
Effect". Final versio
Readout of a quantum processor with high dynamic range Josephson parametric amplifiers
We demonstrate a high dynamic range Josephson parametric amplifier (JPA) in
which the active nonlinear element is implemented using an array of rf-SQUIDs.
The device is matched to the 50 environment with a Klopfenstein-taper
impedance transformer and achieves a bandwidth of 250-300 MHz, with input
saturation powers up to -95 dBm at 20 dB gain. A 54-qubit Sycamore processor
was used to benchmark these devices, providing a calibration for readout power,
an estimate of amplifier added noise, and a platform for comparison against
standard impedance matched parametric amplifiers with a single dc-SQUID. We
find that the high power rf-SQUID array design has no adverse effect on system
noise, readout fidelity, or qubit dephasing, and we estimate an upper bound on
amplifier added noise at 1.6 times the quantum limit. Lastly, amplifiers with
this design show no degradation in readout fidelity due to gain compression,
which can occur in multi-tone multiplexed readout with traditional JPAs.Comment: 9 pages, 8 figure
Measurement-Induced State Transitions in a Superconducting Qubit: Within the Rotating Wave Approximation
Superconducting qubits typically use a dispersive readout scheme, where a
resonator is coupled to a qubit such that its frequency is qubit-state
dependent. Measurement is performed by driving the resonator, where the
transmitted resonator field yields information about the resonator frequency
and thus the qubit state. Ideally, we could use arbitrarily strong resonator
drives to achieve a target signal-to-noise ratio in the shortest possible time.
However, experiments have shown that when the average resonator photon number
exceeds a certain threshold, the qubit is excited out of its computational
subspace, which we refer to as a measurement-induced state transition. These
transitions degrade readout fidelity, and constitute leakage which precludes
further operation of the qubit in, for example, error correction. Here we study
these transitions using a transmon qubit by experimentally measuring their
dependence on qubit frequency, average photon number, and qubit state, in the
regime where the resonator frequency is lower than the qubit frequency. We
observe signatures of resonant transitions between levels in the coupled
qubit-resonator system that exhibit noisy behavior when measured repeatedly in
time. We provide a semi-classical model of these transitions based on the
rotating wave approximation and use it to predict the onset of state
transitions in our experiments. Our results suggest the transmon is excited to
levels near the top of its cosine potential following a state transition, where
the charge dispersion of higher transmon levels explains the observed noisy
behavior of state transitions. Moreover, occupation in these higher energy
levels poses a major challenge for fast qubit reset
Overcoming leakage in scalable quantum error correction
Leakage of quantum information out of computational states into higher energy
states represents a major challenge in the pursuit of quantum error correction
(QEC). In a QEC circuit, leakage builds over time and spreads through
multi-qubit interactions. This leads to correlated errors that degrade the
exponential suppression of logical error with scale, challenging the
feasibility of QEC as a path towards fault-tolerant quantum computation. Here,
we demonstrate the execution of a distance-3 surface code and distance-21
bit-flip code on a Sycamore quantum processor where leakage is removed from all
qubits in each cycle. This shortens the lifetime of leakage and curtails its
ability to spread and induce correlated errors. We report a ten-fold reduction
in steady-state leakage population on the data qubits encoding the logical
state and an average leakage population of less than
throughout the entire device. The leakage removal process itself efficiently
returns leakage population back to the computational basis, and adding it to a
code circuit prevents leakage from inducing correlated error across cycles,
restoring a fundamental assumption of QEC. With this demonstration that leakage
can be contained, we resolve a key challenge for practical QEC at scale.Comment: Main text: 7 pages, 5 figure
Suppressing quantum errors by scaling a surface code logical qubit
Practical quantum computing will require error rates that are well below what
is achievable with physical qubits. Quantum error correction offers a path to
algorithmically-relevant error rates by encoding logical qubits within many
physical qubits, where increasing the number of physical qubits enhances
protection against physical errors. However, introducing more qubits also
increases the number of error sources, so the density of errors must be
sufficiently low in order for logical performance to improve with increasing
code size. Here, we report the measurement of logical qubit performance scaling
across multiple code sizes, and demonstrate that our system of superconducting
qubits has sufficient performance to overcome the additional errors from
increasing qubit number. We find our distance-5 surface code logical qubit
modestly outperforms an ensemble of distance-3 logical qubits on average, both
in terms of logical error probability over 25 cycles and logical error per
cycle ( compared to ). To investigate
damaging, low-probability error sources, we run a distance-25 repetition code
and observe a logical error per round floor set by a single
high-energy event ( when excluding this event). We are able
to accurately model our experiment, and from this model we can extract error
budgets that highlight the biggest challenges for future systems. These results
mark the first experimental demonstration where quantum error correction begins
to improve performance with increasing qubit number, illuminating the path to
reaching the logical error rates required for computation.Comment: Main text: 6 pages, 4 figures. v2: Update author list, references,
Fig. S12, Table I