46 research outputs found
Microwave photon-mediated interactions between semiconductor qubits
The realization of a coherent interface between distant charge or spin qubits
in semiconductor quantum dots is an open challenge for quantum information
processing. Here we demonstrate both resonant and non-resonant photon-mediated
coherent interactions between double quantum dot charge qubits separated by
several tens of micrometers. We present clear spectroscopic evidence of the
collective enhancement of the resonant coupling of two qubits. With both qubits
detuned from the resonator we observe exchange coupling between the qubits
mediated by virtual photons. In both instances pronounced bright and dark
states governed by the symmetry of the qubit-field interaction are found. Our
observations are in excellent quantitative agreement with master-equation
simulations. The extracted two-qubit coupling strengths significantly exceed
the linewidths of the combined resonator-qubit system. This indicates that this
approach is viable for creating photon-mediated two-qubit gates in quantum dot
based systems.Comment: 14 pages, 10 figures and 6 table
Observation of the 4-periodic Josephson effect in indium arsenide nanowires
Quantum computation by non-Abelian Majorana zero modes (MZMs) offers an
approach to achieve fault tolerance by encoding quantum information in the
non-local charge parity states of semiconductor nanowire networks in the
topological superconductor regime. Thus far, experimental studies of MZMs
chiefly relied on single electron tunneling measurements which leads to
decoherence of the quantum information stored in the MZM. As a next step
towards topological quantum computation, charge parity conserving experiments
based on the Josephson effect are required, which can also help exclude
suggested non-topological origins of the zero bias conductance anomaly. Here we
report the direct measurement of the Josephson radiation frequency in InAs
nanowires with epitaxial aluminium shells. For the first time, we observe the
-periodic Josephson effect above a magnetic field of mT,
consistent with the estimated and measured topological phase transition of
similar devices.Comment: Published version. Supplementary Information is available as
ancillary file, raw data and calculations can be downloaded from
http://dx.doi.org/10.4121/uuid:1f936840-5bc2-40ca-8c32-1797c12cacb
Towards high mobility InSb nanowire devices
We study the low-temperature electron mobility of InSb nanowires. We extract
the mobility at 4.2 Kelvin by means of field effect transport measurements
using a model consisting of a nanowire-transistor with contact resistances.
This model enables an accurate extraction of device parameters, thereby
allowing for a systematic study of the nanowire mobility. We identify factors
affecting the mobility, and after optimization obtain a field effect mobility
of cm/Vs. We further demonstrate the
reproducibility of these mobility values which are among the highest reported
for nanowires. Our investigations indicate that the mobility is currently
limited by adsorption of molecules to the nanowire surface and/or the
substrate.Comment: 13 pages, 5 figures (main text); 7 pages, 2 figures, 2 tables
(supplementary text
A gate-tunable, field-compatible fluxonium
Circuit quantum electrodynamics, where photons are coherently coupled to
artificial atoms built with superconducting circuits, has enabled the
investigation and control of macroscopic quantum-mechanical phenomena in
superconductors. Recently, hybrid circuits incorporating semiconducting
nanowires and other electrostatically-gateable elements have provided new
insights into mesoscopic superconductivity. Extending the capabilities of
hybrid flux-based circuits to work in magnetic fields would be especially
useful both as a probe of spin-polarized Andreev bound states and as a possible
platform for topological qubits. The fluxonium is particularly suitable as a
readout circuit for topological qubits due to its unique persistent-current
based eigenstates. In this Letter, we present a magnetic-field compatible
hybrid fluxonium with an electrostatically-tuned semiconducting nanowire as its
non-linear element. We operate the fluxonium in magnetic fields up to 1T and
use it to observe the -Josephson effect. This combination of
gate-tunability and field-compatibility opens avenues for the exploration and
control of spin-polarized phenomena using superconducting circuits and enables
the use of the fluxonium as a readout device for topological qubits
International Guillain-Barré Syndrome Outcome Study (IGOS): protocol of a prospective observational cohort study on clinical and biological predictors of disease course and outcome in Guillain-Barré syndrome
Guillain-Barré syndrome (GBS) is an acute polyradiculoneuropathy with a highly variable clinical presentation, course, and outcome. The factors that determine the clinical variation of GBS are poorly understood which complicates the care and treatment of individual patients. The protocol of the ongoing International GBS Outcome Study (IGOS), a prospective, observational, multi-centre cohort study that aims to identify the clinical and biological determinants and predictors of disease onset, subtype, course and outcome of GBS is presented here. Patients fulfilling the diagnostic criteria for GBS, regardless of age, disease severity, variant forms, or treatment, can participate if included within two weeks after onset of weakness. Information about demography, preceding infections, clinical features, diagnostic findings, treatment, course and outcome is collected. In addition, cerebrospinal fluid and serial blood samples for serum and DNA is collected at standard time points. The original aim was to include at least 1000 patients with a follow-up of 1-3 years. Data are collected via a web-based data entry system and stored anonymously. IGOS started in May 2012 and by January 2017 included more than 1400 participants from 143 active centres in 19 countries across 5 continents. The IGOS data/biobank is available for research projects conducted by expertise groups focusing on specific topics including epidemiology, diagnostic criteria, clinimetrics, electrophysiology, antecedent events, antibodies, genetics, prognostic modelling, treatment effects and long-term outcome of GBS. The IGOS will help to standardize the international collection of data and biosamples for future research of GBS. ClinicalTrials.gov Identifier: NCT01582763
Advances in the treatment of ocular dryness associated with Sjögren׳s syndrome.
BACKGROUND: Sjögren´s syndrome (SS) is an autoimmune rheumatic disease that is characterised by decreased exocrine gland function and frequent ocular symptoms associated with eye dryness. Significantly, dry eyes can lead to corneal abrasions, infection, ulceration, chronic scarring and, in severe cases, perforation. The available conventional therapies have limited efficacy and there are no biologic therapies licensed for use in SS patients. MATERIALS AND METHODS: A literature search of PubMed (MEDLINE) and EMBASE electronic data bases was performed covering the period from January 1994 to September 2014. Evidence was graded in categories I-IV and a treatment algorithm, comprising first line, second line and rescue therapies for ocular dryness associated with SS was proposed. It is based on the current evidence of efficacy of different therapies and explores their link with the pathogenesis of ocular dryness associated with SS. RESULTS: Recent developments in the understanding of the pathogenesis of SS provided evidence that the ocular dryness is associated with pathologic infiltration and dysfunction of the lacrimal glands and changes in the tear composition, together with abnormalities involving the neurosecreting circuits. There is good evidence for the efficacy of topical artificial tears, antiinflammatories and Cyclosporine, and oral Pilocarpine and Cevimeline in controlling the symptoms of ocular dryness associated with SS. CONCLUSIONS: Conventional DMARDs are not particularly effective in addressing the symptoms of ocular dryness associated with SS, despite being commonly prescribed for other SS manifestations. Emerging evidence suggests that B cell and co-stimulatory targeted therapy may play a role in the future
Towards high mobility InSb nanowire devices
\u3cp\u3eWe study the low-temperature electron mobility of InSb nanowires. We extract the mobility at 4.2 K by means of field effect transport measurements using a model consisting of a nanowire-transistor with contact resistances. This model enables an accurate extraction of device parameters, thereby allowing for a systematic study of the nanowire mobility. We identify factors affecting the mobility, and after optimization obtain a field effect mobility of ∼2.5 × 10\u3csup\u3e4\u3c/sup\u3e cm\u3csup\u3e2\u3c/sup\u3e V\u3csup\u3e-1\u3c/sup\u3e s\u3csup\u3e-1\u3c/sup\u3e. We further demonstrate the reproducibility of these mobility values which are among the highest reported for nanowires. Our investigations indicate that the mobility is currently limited by adsorption of molecules to the nanowire surface and/or the substrate.\u3c/p\u3
Realization of microwave quantum circuits using hybrid superconducting-semiconducting nanowire Josephson elements
\u3cp\u3eWe report the realization of quantum microwave circuits using hybrid superconductor-semiconductor Josephson elements comprised of InAs nanowires contacted by NbTiN. Capacitively shunted single elements behave as transmon circuits with electrically tunable transition frequencies. Two-element circuits also exhibit transmonlike behavior near zero applied flux but behave as flux qubits at half the flux quantum, where nonsinusoidal current-phase relations in the elements produce a double-well Josephson potential. These hybrid Josephson elements are promising for applications requiring microwave superconducting circuits operating in a magnetic field.\u3c/p\u3