With the rising societal demand for more information-processing capacity with lower power consumption, alternative architectures inspired by the parallelism and robustness of the human brain have recently emerged as possible solutions. In particular, spiking neural networks (SNNs) offer a bio-realistic approach, relying on pulses, analogous to action potentials, as units of information. While software encoded networks provide flexibility and precision, they are often computationally expensive. As a result, hardware SNNs based on the spiking dynamics of a device or circuit represent an increasingly appealing direction. Here, we propose to use superconducting nanowires as a platform for the development of an artificial neuron. Building on an architecture first proposed for Josephson junctions, we rely on the intrinsic non-linearity of two coupled nanowires to generate spiking behavior, and use electrothermal circuit simulations to demonstrate that the nanowire neuron reproduces multiple characteristics of biological neurons. Furthermore, by harnessing the non-linearity of the superconducting nanowire’s inductance, we develop a design for a variable inductive synapse capable of both excitatory and inhibitory control. We demonstrate that this synapse design supports direct fan-out, a feature that has been difficult to achieve in other superconducting architectures, and that the nanowire neuron’s nominal energy performance is competitive with that of current technologies.

A complete description of the work may be found here.

At the surfaces of nanostructures, enhanced electric fields can drive optical-field photoemission and thereby generate and control electrical currents at frequencies exceeding 100 THz. A hallmark of such optical-field photoemission is the sensitivity of the total emitted current to the carrier-envelope phase (CEP). Here, we examine CEP-sensitive photoemission from plasmonic gold nanoantennas excited with few-cycle optical pulses. At a critical pulse energy, which we call a vanishing point, we observe a pronounced dip in the magnitude of the CEP-sensitive photocurrent accompanied by a sudden shift of π radians in the photocurrent phase. Analysis shows that this vanishing behaviour arises due to competition between sub-optical-cycle electron emission events from neighbouring optical half-cycles and that both the dip and phase shift are highly sensitive to the precise shape of the driving optical waveform at the surface of the emitter. As the mechanisms underlying the dip and phase shift are a general consequence of nonlinear, field-driven photoemission, they may be used to probe sub-optical-cycle emission processes from solid-state emitters, atoms and molecules. Improved understanding of these CEP-sensitive photocurrent features will be critical to the development of optical-field-driven photocathodes for time-domain metrology and microscopy applications demanding attosecond temporal and nanometre spatial resolution.

A complete description of the work may be found here.

Congratulations to Emily for being awarded the 3rd prize in the “Schnitzer Prize in the Visual Arts” contest.
Established in 1996, the Harold and Arlene Schnitzer Prize is awarded each year to current MIT undergraduate and graduate students for excellence in a body of work. Students submit their artistic portfolios for consideration. The 2019 Schnitzer Prize winners attest to the broad range of visual artistic expression that thrives at MIT.

Congratulations to Emily Toomey for being selected as 2019 AAAS Mass Media Fellow.
The AAAS Mass Media Fellowship is a competitive program aimed at encouraging communication in science and fostering connections between scientists and journalists. Each year, fellows are placed at media organizations nationwide for ten weeks to write and report on the latest news in science, and to explain scientific concepts to a broad audience. This year, 26 fellows were selected based on resumes, writing samples, and recommendations. Emily will be working at Smithsonian Magazine in Washington, D.C.

The authors present the use of a commercially available fixed-angle multiwavelength ellipsometer for quickly measuring the thickness of NbN thin films for the fabrication and performance improvement of superconducting nanowire single photon detectors. The process can determine the optical constants of absorbing thin films, removing the need for inaccurate approximations. The tool can be used to observe oxidation growth and allows thickness measurements to be integrated into the characterization of various fabrication processes.

A complete description of the work may be found here.