Scaling of Majorana Zero-Bias Conductance Peaks Nichele, Fabrizio; Drachmann, Asbjørn C C; Whiticar, Alexander M ...
Physical review letters,
09/2017, Volume:
119, Issue:
13
Journal Article
Peer reviewed
Open access
We report an experimental study of the scaling of zero-bias conductance peaks compatible with Majorana zero modes as a function of magnetic field, tunnel coupling, and temperature in one-dimensional ...structures fabricated from an epitaxial semiconductor-superconductor heterostructure. Results are consistent with theory, including a peak conductance that is proportional to tunnel coupling, saturates at 2e^{2}/h, decreases as expected with field-dependent gap, and collapses onto a simple scaling function in the dimensionless ratio of temperature and tunnel coupling.
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Transport is non-reciprocal when not only the sign, but also the absolute value of the current depends on the polarity of the applied voltage. It requires simultaneously broken inversion and ...time-reversal symmetries, for example, by an interplay of spin-orbit coupling and magnetic field. Hitherto, observation of nonreciprocity was tied to resistivity, and dissipationless non-reciprocal circuit elements were elusive. Here we engineer fully superconducting non-reciprocal devices based on highly transparent Josephson junctions fabricated on InAs quantum wells. We demonstrate supercurrent rectification far below the transition temperature. By measuring Josephson inductance, we can link the non-reciprocal supercurrent to an asymmetry of the current-phase relation, and directly derive the supercurrent magnetochiral anisotropy coefficient. A semiquantitative model explains well the main features of our experimental data. Non-reciprocal Josephson junctions have the potential to become for superconducting circuits what pn junctions are for traditional electronics, enabling new non-dissipative circuit elements.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Majorana zero modes-quasiparticle states localized at the boundaries of topological superconductors-are expected to be ideal building blocks for fault-tolerant quantum computing
. Several ...observations of zero-bias conductance peaks measured by tunnelling spectroscopy above a critical magnetic field have been reported as experimental indications of Majorana zero modes in superconductor-semiconductor nanowires
. On the other hand, two-dimensional systems offer the alternative approach of confining Majorana channels within planar Josephson junctions, in which the phase difference φ between the superconducting leads represents an additional tuning knob that is predicted to drive the system into the topological phase at lower magnetic fields than for a system without phase bias
. Here we report the observation of phase-dependent zero-bias conductance peaks measured by tunnelling spectroscopy at the end of Josephson junctions realized on a heterostructure consisting of aluminium on indium arsenide. Biasing the junction to φ ≈ π reduces the critical field at which the zero-bias peak appears, with respect to φ = 0. The phase and magnetic-field dependence of the zero-energy states is consistent with a model of Majorana zero modes in finite-size Josephson junctions. As well as providing experimental evidence of phase-tuned topological superconductivity, our devices are compatible with superconducting quantum electrodynamics architectures
and are scalable to the complex geometries needed for topological quantum computing
.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
The coherent tunnelling of Cooper pairs across Josephson junctions (JJs) generates a nonlinear inductance that is used extensively in quantum information processors based on superconducting circuits, ...from setting qubit transition frequencies
and interqubit coupling strengths
to the gain of parametric amplifiers
for quantum-limited readout. The inductance is either set by tailoring the metal oxide dimensions of single JJs, or magnetically tuned by parallelizing multiple JJs in superconducting quantum interference devices with local current-biased flux lines. JJs based on superconductor-semiconductor hybrids represent a tantalizing all-electric alternative. The gatemon is a recently developed transmon variant that employs locally gated nanowire superconductor-semiconductor JJs for qubit control
. Here we go beyond proof-of-concept and demonstrate that semiconducting channels etched from a wafer-scale two-dimensional electron gas (2DEG) are a suitable platform for building a scalable gatemon-based quantum computer. We show that 2DEG gatemons meet the requirements
by performing voltage-controlled single qubit rotations and two-qubit swap operations. We measure qubit coherence times up to ~2 μs, limited by dielectric loss in the 2DEG substrate.
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Stress Modulation of Fracture Fixation Implants Beltran, Michael J; Collinge, Cory A; Gardner, Michael J
Journal of the American Academy of Orthopaedic Surgeons,
2016-October, Volume:
24, Issue:
10
Journal Article
Peer reviewed
Stress modulation is the concept of manipulating bridge plate variables to provide a flexible fixation construct that allows callus formation through uneventful secondary bone healing. Obtaining ...absolute stability through the anatomic reduction of all fracture fragments comes at the expense of fracture biology, whereas intramedullary nailing, which is more advantageous for diaphyseal fractures of the lower extremity, is technically demanding and often may not be possible when stabilizing many metaphyseal fractures. Overly stiff plating constructs are associated with asymmetric callus formation, early implant failure, and fracture nonunion. Numerous surgeon-controlled variables can be manipulated to increase flexibility without sacrificing strength, including using longer plates with well-spaced screws, choosing titanium or stainless steel implants, and using locking or nonlocking screws. Axially dynamic emerging concepts, such as far cortical locking and near cortical overdrilling, provide further treatment options when bridge plating techniques are used.
Raman spectroscopy can be used to measure the chemical composition of a sample, which can in turn be used to extract biological information. Many materials have characteristic Raman spectra, which ...means that Raman spectroscopy has proven to be an effective analytical approach in geology, semiconductor, materials and polymer science fields. The application of Raman spectroscopy and microscopy within biology is rapidly increasing because it can provide chemical and compositional information, but it does not typically suffer from interference from water molecules. Analysis does not conventionally require extensive sample preparation; biochemical and structural information can usually be obtained without labeling. In this protocol, we aim to standardize and bring together multiple experimental approaches from key leaders in the field for obtaining Raman spectra using a microspectrometer. As examples of the range of biological samples that can be analyzed, we provide instructions for acquiring Raman spectra, maps and images for fresh plant tissue, formalin-fixed and fresh frozen mammalian tissue, fixed cells and biofluids. We explore a robust approach for sample preparation, instrumentation, acquisition parameters and data processing. By using this approach, we expect that a typical Raman experiment can be performed by a nonspecialist user to generate high-quality data for biological materials analysis.
IR spectroscopy is an excellent method for biological analyses. It enables the nonperturbative, label-free extraction of biochemical information and images toward diagnosis and the assessment of cell ...functionality. Although not strictly microscopy in the conventional sense, it allows the construction of images of tissue or cell architecture by the passing of spectral data through a variety of computational algorithms. Because such images are constructed from fingerprint spectra, the notion is that they can be an objective reflection of the underlying health status of the analyzed sample. One of the major difficulties in the field has been determining a consensus on spectral pre-processing and data analysis. This manuscript brings together as coauthors some of the leaders in this field to allow the standardization of methods and procedures for adapting a multistage approach to a methodology that can be applied to a variety of cell biological questions or used within a clinical setting for disease screening or diagnosis. We describe a protocol for collecting IR spectra and images from biological samples (e.g., fixed cytology and tissue sections, live cells or biofluids) that assesses the instrumental options available, appropriate sample preparation, different sampling modes as well as important advances in spectral data acquisition. After acquisition, data processing consists of a sequence of steps including quality control, spectral pre-processing, feature extraction and classification of the supervised or unsupervised type. A typical experiment can be completed and analyzed within hours. Example results are presented on the use of IR spectra combined with multivariate data processing.
Zero deforestation commitments (ZDCs) are voluntary initiatives where companies or countries pledge to eliminate deforestation from their supply chains. These commitments offer much promise for ...sustainable commodity production, but are undermined by a lack of transparency about their coverage and impacts. Here, using state-of-the-art supply chain data, we introduce an approach to evaluate the impact of ZDCs, linking traders and international markets to commodity-associated deforestation in the sub-national jurisdictions from which they source. We focus on the Brazilian soy sector, where we find that ZDC coverage is increasing, but under-represents the Cerrado biome where most soy-associated deforestation currently takes place. Though soy-associated deforestation declined in the Amazon after the introduction of the Soy Moratorium, we observe no change in the exposure of companies or countries adopting ZDCs to soy-associated deforestation in the Cerrado. We further assess the formulation and implementation of these ZDCs and identify several systematic weaknesses that must be addressed to increase the likelihood that they achieve meaningful reductions in deforestation in future. As the 2020 deadline for several of these commitments approaches, our approach can provide independent monitoring of progress toward the goal of ending commodity-associated deforestation.
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