System Bits: Nov. 11

How transistors operate at absolute zero
Research led by scientists at Chalmers University of Technology in Sweden and Caltech in California have demonstrated how noise in a microwave amplifier is limited by self-heating at very low temperatures, which is expected to be of importance for future discoveries in such as quantum computers and radio astronomy.

The team also included researchers from the University of Salamanca and the Swedish company Low Noise Factory.

The work study is important for the fundamental understanding of how a transistor operates close to absolute zero temperature, and also how even more sensitive low-noise amplifiers should be designed for future detectors in physics and astronomy.

Cross sectional image of an ultra-low noise transistor. Electrons, accelerated in the high mobility channel under the 100nm gate, collide and dissipate heat that fundamentally limits the noise performance of the transistor.
(Source: Chalmers University of Technology)

Faint microwave signals are detected by transistor-based low-noise amplifiers, and the researchers have optimized indium phosphide transistors using a special process for this purpose.

Accelerating particles with plasma
A technique for accelerating electrons on waves of plasma has been developed by researchers from UCLA and the Department of Energy’s SLAC National Accelerator Laboratory that is efficient enough to power a new generation of shorter, more economical accelerators— greatly expand their potential use in areas such as medicine, national security, industry and high-energy physics research.

This achievement is a milestone in demonstrating the technique of plasma wakefield acceleration, in which electrons gain energy by essentially surfing on a wave of electrons within an ionized gas.

Chandrashekhar Joshi, professor of electrical engineering at the UCLA Henry Samueli School of Engineering and Applied Science, led the team that developed the plasma source used in the experiment.

Computer simulation of a wake produced by an intense electron bunch as it passes through an ionized gas from left to right. (Source: UCLA)

Plasma wakefields have been of interest to accelerator physicists for 35 years as one of the more promising ways to drive the smaller, cheaper accelerators of the future. The UCLA and SLAC groups have been at the forefront of research on plasma wakefield acceleration for more than a decade.