450 research outputs found
Photon Assisted Tunneling of Zero Modes in a Majorana Wire
Hybrid nanowires with proximity-induced superconductivity in the topological
regime host Majorana zero modes (MZMs) at their ends, and networks of such
structures can produce topologically protected qubits. In a double-island
geometry where each segment hosts a pair of MZMs, inter-pair coupling mixes the
charge parity of the islands and opens an energy gap between the even and odd
charge states at the inter-island charge degeneracy. Here, we report on the
spectroscopic measurement of such an energy gap in an InAs/Al double-island
device by tracking the position of the microwave-induced quasiparticle (qp)
transitions using a radio-frequency (rf) charge sensor. In zero magnetic field,
photon assisted tunneling (PAT) of Cooper pairs gives rise to resonant lines in
the 2e-2e periodic charge stability diagram. In the presence of a magnetic
field aligned along the nanowire, resonance lines are observed parallel to the
inter-island charge degeneracy of the 1e-1e periodic charge stability diagram,
where the 1e periodicity results from a zero-energy sub-gap state that emerges
in magnetic field. Resonant lines in the charge stability diagram indicate
coherent photon assisted tunneling of single-electron states, changing the
parity of the two islands. The dependence of resonant frequency on detuning
indicates a sizable (GHz-scale) hybridization of zero modes across the junction
separating islands
Magnetic-field-induced transition in a quantum dot coupled to a superconductor
The magnetic moment of a quantum dot can be screened by its coupling to a superconducting reservoir, depending on the hierarchy of the superconducting gap and the relevant Kondo scale. This screening-unscreening transition can be driven by electrostatic gating, tunnel coupling, and, as we demonstrate here, a magnetic field. We perform high-resolution spectroscopy of subgap excitations near the screening-unscreening transition of asymmetric superconductor-quantum dot-superconductor (S-QD-S) junctions formed by the electromigration technique. Our measurements reveal a re-entrant phase boundary determined by the competition between Zeeman energy and gap reduction with magnetic field. We further track the evolution of the phase transition with increasing temperature, which is also evinced by thermal replicas of subgap states
Electrical Properties of Selective-Area-Grown Superconductor-Semiconductor Hybrid Structures on Silicon
We present a superconductor-semiconductor material system that is both
scalable and monolithically integrated on a silicon substrate. It uses
selective area growth of Al-InAs hybrid structures on a planar III-V buffer
layer, grown directly on a high resistivity silicon substrate. We characterized
the electrical properties of this material system at millikelvin temperatures
and observed a high average field-effect mobility of for the InAs channel, and a hard induced
superconducting gap. Josephson junctions exhibited a high interface
transmission, , gate voltage tunable switching
current with a product of critical current and normal state resistance,
, and signatures of
multiple Andreev reflections. These results pave the way for scalable and high
coherent gate voltage tunable transmon devices and other
superconductor-semiconductor hybrids fabricated directly on silicon
Observations of entrainment in eastern Pacific marine stratocumulus using three conserved scalars
Engineering access to higher education through higher education fairs
Text from van Zanten A., Legavre A. “Engineering access to higher education through higher education fairs”, in Goastellec G., Picard F. (ed.) The Roles of Higher Education and Research in the Fabric of Societies, Leuven, Sense Publishers, 2014 (in press).
Transition to higher education is a major social process. This transition has been mostly studied by French sociologists of education and higher education from perspectives focusing predominantly on the role of the socio-economic status, academic profiles and different tracks followed by secondary school students (Merle 1996, Duru-Bellat and Kieffer 2008, Convert 2010), and, to a lesser extent, on the types of secondary schools attended (Duru-Bellat and Mingat 1998, Nakhili 2005) and the local higher education provision (Berthet et al. 2010, Orange 2013). Although these structural determinants play a major role in explaining significant regularities, they provide more powerful explanations for individuals representing the extremes of the different variables considered, leaving room for the influence of other major factors for those students in intermediate situations. In addition, even in the case of students occupying extreme positions, structural perspectives better explain the distribution of students between different higher education tracks than they do between institutions and disciplines.
In this chapter, we adopt a perspective that we see as complementary to and interacting with the perspective centred on structural determinants by focusing on the role of the devices that mediate the exchanges between students and higher education institutions, and more specifically on one device: higher education fairs.
Our purpose in doing so is not only to document how these various devices frame, in ways that remain largely unexplored by researchers, exchanges between providers and consumers of higher education but also to point out – and further explore in future publications – how these devices, and the specific features of fairs, contribute to the reproduction and transformation of educational inequalities in access to higher education (Benninghoff et al. 2012)
Gate-Tunable Transmon Using Selective-Area-Grown Superconductor-Semiconductor Hybrid Structures on Silicon
We present a gate-voltage tunable transmon qubit (gatemon) based on planar
InAs nanowires that are selectively grown on a high resistivity silicon
substrate using III-V buffer layers. We show that low loss superconducting
resonators with an internal quality of can readily be realized
using these substrates after the removal of buffer layers. We demonstrate
coherent control and readout of a gatemon device with a relaxation time,
, and dephasing times, and .
Further, we infer a high junction transparency of from an analysis
of the qubit anharmonicity
Transitioning to molecular diagnostics in pediatric high-grade glioma: Experiences with the 2016 WHO classification of CNS tumors
BACKGROUND:
Pediatric neuro-oncology was profoundly changed in the wake of the 2016 revision of the WHO Classification of Tumors of the Central Nervous System. Practitioners were challenged to quickly adapt to a system of tumor classification redefined by molecular diagnostics.
METHODS:
We designed a 22-question survey studying the impact of the revised WHO classification on pediatric high-grade glioma. The survey collected basic demographics, general attitudes, issues encountered, and opinions on pediatric subtypes. Participant answers were analyzed along socioeconomic lines utilizing the human development index (HDI) of the United Nations and membership in the group of seven (G7) world economic forum.
RESULTS:
Four hundred and sixty-five participants from 53 countries were included, 187 pediatric neurooncologists (40%), 160 neuropathologists (34%), and 118 other experts (26%). When asked about pediatric high-grade glioma entities, participants from very high development countries preferred treating a patient based on genetic findings. Participants from high and medium development countries indicated using traditional histology and tumor location as mainstays for therapeutic decisions. Non-G7 countries tended to regard the introduction of molecularly characterized tumor entities as a problem for daily routine due to lack of resources.
CONCLUSIONS:
Our findings demonstrate an overall greater reliance and favorability to molecular diagnostics among very high development countries. A disparity in resources and access to molecular diagnostics has left some centers unable to classify pediatric high-grade glioma per the WHO classification. The forthcoming edition should strain to abate disparities in molecular diagnostic availability and work toward universal adaptation
Probing structural relaxation in complex fluids by critical fluctuations
Complex fluids, such as polymer solutions and blends, colloids and gels, are
of growing interest in fundamental and applied soft-condensed-matter science. A
common feature of all such systems is the presence of a mesoscopic structural
length scale intermediate between atomic and macroscopic scales. This
mesoscopic structure of complex fluids is often fragile and sensitive to
external perturbations. Complex fluids are frequently viscoelastic (showing a
combination of viscous and elastic behaviour) with their dynamic response
depending on the time and length scales. Recently, non-invasive methods to
infer the rheological response of complex fluids have gained popularity through
the technique of microrheology, where the diffusion of probe spheres in a
viscoelastic fluid is monitored with the aid of light scattering or microscopy.
Here we propose an alternative to traditional microrheology that does not
require doping of probe particles in the fluid (which can sometimes drastically
alter the molecular environment). Instead, our proposed method makes use of the
phenomenon of "avoided crossing" between modes associated with the structural
relaxation and critical fluctuations that are spontaneously generated in the
system.Comment: 4 pages, 4 figure
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