214 research outputs found
Effects of the electrostatic environment on superlattice Majorana nanowires
Finding ways of creating, measuring, and manipulating Majorana bound states (MBSs) in superconducting-semiconducting nanowires is a highly pursued goal in condensed matter physics. It was recently proposed that a periodic covering of the semiconducting nanowire with superconductor fingers would allow both gating and tuning the system into a topological phase while leaving room for a local detection of the MBS wave function. We perform a detailed, self-consistent numerical study of a three-dimensional (3D) model for a finite-length nanowire with a superconductor superlattice including the effect of the surrounding electrostatic environment, and taking into account the surface charge created at the semiconductor surface. We consider different experimental scenarios where the superlattice is on top or at the bottom of the nanowire with respect to a back gate. The analysis of the 3D electrostatic profile, the charge density, the low-energy spectrum, and the formation of MBSs reveals a rich phenomenology that depends on the nanowire parameters as well as on the superlattice dimensions and the external back-gate potential. The 3D environment turns out to be essential to correctly capture and understand the phase diagram of the system and the parameter regions where topological superconductivity is establishedWe thank E. J. H. Lee, H. Beidenkopf, E. G. Michel, N. Avraham, H. Shtrikman, and J. Nygård for valuable discussions. Research supported by the Spanish MINECO through Grants No. FIS2016-80434-P, No. BES-2017-080374, and No. FIS2017-84860-R (AEI/FEDER, EU), the European Union's Horizon 2020 research and innovation programme under the FETOPEN Grant Agreement No. 828948 and Grant Agreement LEGOTOP No. 788715, the Ramón y Cajal programme RYC-2011-09345, the María de Maeztu Programme for Units of Excellence in R&D (MDM-2014-0377), the DFG (CRC/Transregio 183, EI 519/7- 1), the Israel Science Foundation (ISF), and the Binational Science Foundation (BSF
Tunable proximity effects and topological superconductivity in ferromagnetic hybrid nanowires
Hybrid semiconducting nanowire devices combining epitaxial superconductor and
ferromagnetic insulator layers have been recently explored experimentally as an
alternative platform for topological superconductivity at zero applied magnetic
field. In this proof-of-principle work we show that the topological regime can
be reached in actual devices depending on some geometrical constraints. To this
end, we perform numerical simulations of InAs wires in which we explicitly
include the superconducting Al and magnetic EuS shells, as well as the
interaction with the electrostatic environment at a self-consistent mean-field
level. Our calculations show that both the magnetic and the superconducting
proximity effects on the nanowire can be tuned by nearby gates thanks to their
ability to move the wavefunction across the wire section. We find that the
topological phase is achieved in significant portions of the phase diagram only
in configurations where the Al and EuS layers overlap on some wire facet, due
to the rather local direct induced spin polarization and the appearance of an
extra indirect exchange field through the superconductor. While of obvious
relevance for the explanation of recent experiments, tunable proximity effects
are of interest in the broader field of superconducting spintronics.Comment: 16 pages, 11 figures. v2: final versio
Pick-a-Pic: An Open Dataset of User Preferences for Text-to-Image Generation
The ability to collect a large dataset of human preferences from
text-to-image users is usually limited to companies, making such datasets
inaccessible to the public. To address this issue, we create a web app that
enables text-to-image users to generate images and specify their preferences.
Using this web app we build Pick-a-Pic, a large, open dataset of text-to-image
prompts and real users' preferences over generated images. We leverage this
dataset to train a CLIP-based scoring function, PickScore, which exhibits
superhuman performance on the task of predicting human preferences. Then, we
test PickScore's ability to perform model evaluation and observe that it
correlates better with human rankings than other automatic evaluation metrics.
Therefore, we recommend using PickScore for evaluating future text-to-image
generation models, and using Pick-a-Pic prompts as a more relevant dataset than
MS-COCO. Finally, we demonstrate how PickScore can enhance existing
text-to-image models via ranking
Faulting and Folding of the Transgressive Surface Offshore Ventura Records Deformational Events in the Holocene
Identifying the offshore thrust faults of the Western Transverse Ranges that could produce large earthquakes and seafloor uplift is essential to assess potential geohazards for the region. The Western Transverse Ranges in southern California are an E-W trending fold-and-thrust system that extends offshore west of Ventura. Using a high-resolution seismic CHIRP dataset, we have identified the Last Glacial Transgressive Surface (LGTS) and two Holocene seismostratigraphic units. Deformation of the LGTS, together with onlapping packages that exhibit divergence and rotation across the active structures, provide evidence for three to four deformational events with vertical uplifts ranging from 1 to 10 m. Based on the depth of the LGTS and the Holocene sediment thickness, age estimates for the deformational events reveal a good correlation with the onshore paleoseismological results for the Ventura-Pitas Point fault and the Ventura-Avenue anticline. The observed deformation along the offshore segments of the Ventura-Pitas Point fault and Ventura-Avenue anticline trend diminishes toward the west. Farther north, the deformation along the offshore Red Mountain anticline also diminishes to the west with the shortening stepping north onto the Mesa-Rincon Creek fault system. These observations suggest that offshore deformation along the fault-fold structures moving westward is systematically stepping to the north toward the hinterland. The decrease in the amount of deformation along the frontal structures towards the west corresponds to an increase in deformation along the hinterland fold systems, which could result from a connection of the fault strands at depth. A connection at depth of the northward dipping thrusts to a regional master detachment may explain the apparent jump of the deformation moving west, from the Ventura-Pitas Point fault and the Ventura-Avenue anticline to the Red Mountain anticline, and then, from the Red Mountain anticline to the Mesa-Rincon Creek fold system. Finally, considering the maximum vertical uplift estimated for events on these structures (max ∼10 m), along with the potential of a common master detachment that may rupture in concert, this system could generate a large magnitude earthquake (>Mw 7.0) and a consequent tsunami.Depto. de Geodinámica, Estratigrafía y PaleontologíaFac. de Ciencias GeológicasTRUEUnión Europea. Horizonte 2020Comunidad de MadridSCECpu
RadArnomaly: Protecting Radar Systems from Data Manipulation Attacks
Radar systems are mainly used for tracking aircraft, missiles, satellites,
and watercraft. In many cases, information regarding the objects detected by
the radar system is sent to, and used by, a peripheral consuming system, such
as a missile system or a graphical user interface used by an operator. Those
systems process the data stream and make real-time, operational decisions based
on the data received. Given this, the reliability and availability of
information provided by radar systems has grown in importance. Although the
field of cyber security has been continuously evolving, no prior research has
focused on anomaly detection in radar systems. In this paper, we present a deep
learning-based method for detecting anomalies in radar system data streams. We
propose a novel technique which learns the correlation between numerical
features and an embedding representation of categorical features in an
unsupervised manner. The proposed technique, which allows the detection of
malicious manipulation of critical fields in the data stream, is complemented
by a timing-interval anomaly detection mechanism proposed for the detection of
message dropping attempts. Real radar system data is used to evaluate the
proposed method. Our experiments demonstrate the method's high detection
accuracy on a variety of data stream manipulation attacks (average detection
rate of 88% with 1.59% false alarms) and message dropping attacks (average
detection rate of 92% with 2.2% false alarms)
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