79 research outputs found
High-order noise filtering in nontrivial quantum logic gates
Treating the effects of a time-dependent classical dephasing environment
during quantum logic operations poses a theoretical challenge, as the
application of non-commuting control operations gives rise to both dephasing
and depolarization errors that must be accounted for in order to understand
total average error rates. We develop a treatment based on effective
Hamiltonian theory that allows us to efficiently model the effect of classical
noise on nontrivial single-bit quantum logic operations composed of arbitrary
control sequences. We present a general method to calculate the
ensemble-averaged entanglement fidelity to arbitrary order in terms of noise
filter functions, and provide explicit expressions to fourth order in the noise
strength. In the weak noise limit we derive explicit filter functions for a
broad class of piecewise-constant control sequences, and use them to study the
performance of dynamically corrected gates, yielding good agreement with
brute-force numerics.Comment: Revised and expanded to include filter function terms beyond first
order in the Magnus expansion. Related manuscripts available from
http://www.physics.usyd.edu.au/~mbiercu
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A national strategy to promote Open Educational Practices in higher education in Australia
Currently in Australia, there are no policies and regulations at national levels to promote and encourage the adoption of Open Educational Practices (OEP) across the higher education sector. As an attempt to bridge this policy gap, a project proposal was developed by a group of OEP advocates and researchers and then successfully funded by the Australian Government Department of Education and Training (AGDET). This paper explores and discusses the approaches, deliverables and recommendations of this project titled Students, Universities and Open Education (OpenEdOz) Project. One of its main deliverables was a National Policy Roadmap, which aimed to assist the government to realise the potential of OEP for the Australian higher education sector and open up opportunities for further national policy development and support in which OEP can flourish. The policy roadmap was informed by a range of national and international evidenced-based case studies related to OEP projects and initiatives
Experimental Uhrig Dynamical Decoupling using Trapped Ions
We present a detailed experimental study of the Uhrig Dynamical Decoupling
(UDD) sequence in a variety of noise environments. Our qubit system consists of
a crystalline array of Be ions confined in a Penning trap. We use
an electron-spin-flip transition as our qubit manifold and drive qubit
rotations using a 124 GHz microwave system. We study the effect of the UDD
sequence in mitigating phase errors and compare against the well known
CPMG-style multipulse spin echo as a function of pulse number, rotation axis,
noise spectrum, and noise strength. Our results agree well with theoretical
predictions for qubit decoherence in the presence of classical phase noise,
accounting for the effect of finite-duration pulses. Finally, we
demonstrate that the Uhrig sequence is more robust against systematic
over/underrotation and detuning errors than is multipulse spin echo, despite
the precise prescription for pulse-timing in UDD
Direct Measurement of the System-Environment Coupling as a Tool For Understanding Decoherence and Dynamical Decoupling
Decoherence is a major obstacle to any practical implementation of quantum
information processing. One of the leading strategies to reduce decoherence is
dynamical decoupling --- the use of an external field to average out the effect
of the environment. The decoherence rate under any control field can be
calculated if the spectrum of the coupling to the environment is known. We
present a direct measurement of the bath coupling spectrum in an ensemble of
optically trapped ultracold atoms, by applying a spectrally narrow-band control
field. The measured spectrum follows a Lorentzian shape at low frequencies, but
exhibits non-monotonic features at higher frequencies due to the oscillatory
motion of the atoms in the trap. These features agree with our analytical
models and numerical Monte-Carlo simulations of the collisional bath. From the
inferred bath-coupling spectrum, we predict the performance of well-known
dynamical decoupling sequences: CPMG, UDD and CDD. We then apply these
sequences in experiment and compare the results to predictions, finding good
agreement in the weak-coupling limit. Thus, our work establishes experimentally
the validity of the overlap integral formalism, and is an important step
towards the implementation of an optimal dynamical decoupling sequence for a
given measured bath spectrum.Comment: 9 pages, 6 figure
Ultrasensitive force and displacement detection using trapped ions
The ability to detect extremely small forces is vital for a variety of
disciplines including precision spin-resonance imaging, microscopy, and tests
of fundamental physical phenomena. Current force-detection sensitivity limits
have surpassed 1 (atto ) through coupling of micro or
nanofabricated mechanical resonators to a variety of physical systems including
single-electron transistors, superconducting microwave cavities, and individual
spins. These experiments have allowed for probing studies of a variety of
phenomena, but sensitivity requirements are ever-increasing as new regimes of
physical interactions are considered. Here we show that trapped atomic ions are
exquisitely sensitive force detectors, with a measured sensitivity more than
three orders of magnitude better than existing reports. We demonstrate
detection of forces as small as 174 (yocto ), with a
sensitivity 390 using crystals of Be
ions in a Penning trap. Our technique is based on the excitation of normal
motional modes in an ion trap by externally applied electric fields, detection
via and phase-coherent Doppler velocimetry, which allows for the discrimination
of ion motion with amplitudes on the scale of nanometers. These experimental
results and extracted force-detection sensitivities in the single-ion limit
validate proposals suggesting that trapped atomic ions are capable of detecting
of forces with sensitivity approaching 1 . We anticipate that
this demonstration will be strongly motivational for the development of a new
class of deployable trapped-ion-based sensors, and will permit scientists to
access new regimes in materials science.Comment: Expanded introduction and analysis. Methods section added. Subject to
press embarg
IT adoption of clinical information systems in Austrian and German hospitals: results of a comparative survey with a focus on nursing
<p>Abstract</p> <p>Background</p> <p>IT adoption is a process that is influenced by different external and internal factors. This study aimed</p> <p indent="1">1. to identify similarities and differences in the prevalence of medical and nursing IT systems in Austrian and German hospitals, and</p> <p indent="1">2. to match these findings with characteristics of the two countries, in particular their healthcare system, and with features of the hospitals.</p> <p>Methods</p> <p>In 2007, all acute care hospitals in both countries received questionnaires with identical questions. 12.4% in Germany and 34.6% in Austria responded.</p> <p>Results</p> <p>The surveys revealed a consistent higher usage of nearly all clinical IT systems, especially nursing systems, but also PACS and electronic archiving systems, in Austrian than in German hospitals. These findings correspond with a significantly wider use of standardised nursing terminologies and a higher number of PC workstations on the wards (average 2.1 PCs in Germany, 3.2 PCs in Austria). Despite these differences, Austrian and German hospitals both reported a similar IT budget of 2.6% in Austria and 2.0% in Germany (median).</p> <p>Conclusions</p> <p>Despite the many similarities of the Austrian and German healthcare system there are distinct differences which may have led to a wider use of IT systems in Austrian hospitals. In nursing, the specific legal requirement to document nursing diagnoses in Austria may have stimulated the use of standardised terminologies for nursing diagnoses and the implementation of electronic nursing documentation systems. Other factors which correspond with the wider use of clinical IT systems in Austria are: good infrastructure of medical-technical devices, rigorous organisational changes which had led to leaner processes and to a lower length of stay, and finally a more IT friendly climate. As country size is the most pronounced difference between Germany and Austria it could be that smaller countries, such as Austria, are more ready to translate innovation into practice.</p
Imbalances in serum angiopoietin concentrations are early predictors of septic shock development in patients with post chemotherapy febrile neutropenia
Background: Febrile neutropenia carries a high risk of sepsis complications, and the identification of biomarkers capable to identify high risk patients is a great challenge. Angiopoietins (Ang -) are cytokines involved in the control microvascular permeability. It is accepted that Ang-1 expression maintains endothelial barrier integrity, and that Ang-2 acts as an antagonizing cytokine with barrier-disrupting functions in inflammatory situations. Ang-2 levels have been recently correlated with sepsis mortality in intensive care units. Methods: We prospectively evaluated concentrations of Ang-1 and Ang-2 at different time-points during febrile neutropenia, and explored the diagnostic accuracy of these mediators as potential predictors of poor outcome in this clinical setting before the development of sepsis complications. Results: Patients that evolved with septic shock (n = 10) presented higher levels of Ang-2 measured 48 hours after fever onset, and of the Ang-2/Ang-1 ratio at the time of fever onset compared to patients with non-complicated sepsis (n = 31). These levels correlated with sepsis severity scores. Conclusions: Our data suggest that imbalances in the concentrations of Ang-1 and Ang-2 are independent and early markers of the risk of developing septic shock and of sepsis mortality in febrile neutropenia, and larger studies are warranted to validate their clinical usefulness. Therapeutic strategies that manipulate this Ang-2/Ang-1 imbalance can potentially offer new and promising treatments for sepsis in febrile neutropenia
Optimized Dynamical Decoupling in a Model Quantum Memory
We present experimental measurements on a model quantum system that
demonstrate our ability to dramatically suppress qubit error rates by the
application of optimized dynamical decoupling pulse sequences in a variety of
experimentally relevant noise environments. We provide the first demonstration
of an analytically derived pulse sequence developed by Uhrig, and find novel
sequences through active, real-time experimental feedback. These new sequences
are specially tailored to maximize error suppression without the need for a
priori knowledge of the ambient noise environment. We compare these sequences
against the Uhrig sequence, and the well established CPMG-style spin echo,
demonstrating that our locally optimized pulse sequences outperform all others
under test. Numerical simulations show that our locally optimized pulse
sequences are capable of suppressing errors by orders of magnitude over other
existing sequences. Our work includes the extension of a treatment to predict
qubit decoherence under realistic conditions, including the use of
finite-duration, square pulses, yielding strong agreement between
experimental data and theory for arbitrary pulse sequences. These results
demonstrate the robustness of qubit memory error suppression through dynamical
decoupling techniques across a variety of qubit technologies.Comment: Subject to press embarg
From PALSA PLUS to PALM PLUS: adapting and developing a South African guideline and training intervention to better integrate HIV/AIDS care with primary care in rural health centers in Malawi
<p>Abstract</p> <p>Background</p> <p>Only about one-third of eligible HIV/AIDS patients receive anti-retroviral treatment (ART). Decentralizing treatment is crucial to wider and more equitable access, but key obstacles are a shortage of trained healthcare workers (HCW) and challenges integrating HIV/AIDS care with other primary care. This report describes the development of a guideline and training program (PALM PLUS) designed to integrate HIV/AIDS care with other primary care in Malawi. PALM PLUS was adapted from PALSA PLUS, developed in South Africa, and targets middle-cadre HCWs (clinical officers, nurses, and medical assistants). We adapted it to align with Malawi's national treatment protocols, more varied healthcare workforce, and weaker health system infrastructure.</p> <p>Methods/Design</p> <p>The international research team included the developers of the PALSA PLUS program, key Malawi-based team members and personnel from national and district level Ministry of Health (MoH), professional associations, and an international non-governmental organization. The PALSA PLUS guideline was extensively revised based on Malawi national disease-specific guidelines. Advice and input was sought from local clinical experts, including middle-cadre personnel, as well as Malawi MoH personnel and representatives of Malawian professional associations.</p> <p>Results</p> <p>An integrated guideline adapted to Malawian protocols for adults with respiratory conditions, HIV/AIDS, tuberculosis, and other primary care conditions was developed. The training program was adapted to Malawi's health system and district-level supervision structure. PALM PLUS is currently being piloted in a cluster-randomized trial in health centers in Malawi (ISRCTN47805230).</p> <p>Discussion</p> <p>The PALM PLUS guideline and training intervention targets primary care middle-cadre HCWs with the objective of improving HCW satisfaction and retention, and the quality of patient care. Successful adaptations are feasible, even across health systems as different as those of South Africa and Malawi.</p
Quantum Magnetism of Spin-Ladder Compounds with Trapped-Ion Crystals
The quest for experimental platforms that allow for the exploration, and even
control, of the interplay of low dimensionality and frustration is a
fundamental challenge in several fields of quantum many-body physics, such as
quantum magnetism. Here, we propose the use of cold crystals of trapped ions to
study a variety of frustrated quantum spin ladders. By optimizing the trap
geometry, we show how to tailor the low dimensionality of the models by
changing the number of legs of the ladders. Combined with a method for
selectively hiding of ions provided by laser addressing, it becomes possible to
synthesize stripes of both triangular and Kagome lattices. Besides, the degree
of frustration of the phonon-mediated spin interactions can be controlled by
shaping the trap frequencies. We support our theoretical considerations by
initial experiments with planar ion crystals, where a high and tunable
anisotropy of the radial trap frequencies is demonstrated. We take into account
an extensive list of possible error sources under typical experimental
conditions, and describe explicit regimes that guarantee the validity of our
scheme
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