High-speed method tracks fleeting quantum events

Researchers at NPL have reported a novel high-speed charge sensing method for ballistic electrons, a potentially useful technique in the fields of electron quantum optics, quantum electrical metrology, flying qubit technology, and signal sensing.

The study, published in Physical Review Letters, reveals that the presence of a single ballistic electron can be revealed by tracking the path of another fast-moving “sensing” electron. By steering the paths of these electrons close to each other, the tiny repulsion between them can redirect the sensing electron, like a train switching tracks or cars diverting off a freeway.

When charge sensors are used in quantum devices, they are measured continuously, with each sample long enough to resolve a signal from the noise. The NPL sensing system leverages synchronization between the detector and sensing electrons to achieve extreme time selectivity, only sampling within a minuscule time window and detecting interactions that occur in just 1–2 picoseconds.

To put this in some context, there are various quantum technology platforms in various stages of development, competing to determine which is the most practical for applications. NPL’s work highlights a key feature of the platform based on ballistic electrons in semiconductors.

These systems, which somewhat mimic quantum optical systems, have intrinsically fast time scales of operation. Sensing schemes are one ingredient to build complex single-electron circuits and unlock new quantum technologies.

Jonathan Fletcher, Senior Scientist, said, “All conductors feature ballistic single electron physics at the atomic scale on very short time scales, but it’s unusual to be able to detect this at the single electron level, let alone have direct control. This control and detection is exactly what our system gives you.

“It’s exciting for me because control of electricity at nanometer and picosecond scales is a fundamental tool for metrology and also a pathway to other quantum-enabled capabilities.”