Logo of the Physikalisch-Technische Bundesanstalt
Gateway for school

Controlled collision of two electrons

Novel quantum electronics control the interaction between individual electrons in a semiconductor chip with precise timing

PTB-News 1.2024
Especially interesting for

fundamental research in physics

quantum technology and nanotechnology

Targeted collision of single photons or electrons enables a sensitive measurement method that can be used to investigate and control the way in which they influence each other. This reduction to single sharp signal impulses allows the measurement resolution to be improved and new components to be created for quantum information processing. In nanostructured semiconductor circuits, two separate electrons can be guided ballistically on intersecting signal paths; in this way, the electrons’ interaction can be used to control or probe electrical signals. The basic function of a non-linear circuit component of this type has been demonstrated in distinct, complementary realizations by three independent research teams led by NEEL (F), NPL (UK) and PTB.

Simulation of electronic collision circuit: Two electron sources (S1, S2) simultaneously send indistinguishable electrons down counter-propagating paths. The electrons’ movement within the potential of an electronic beam splitter can be controlled precisely due to their mutual interaction. The outcome is detected by two detectors (D1, D2) that can determine the arrival of an individual electron.

Manipulating and controlling electric current on the basis of single charge carriers in electrical circuits is a significant challenge, since electrical impulses pass through the circuits in very short periods of time due to the small structure sizes involved. However, targeted collision of single electrons within suitable circuits allows the electron stream to be probed with high time resolution. The way in which an electron collision circuit functions is similar to attempting to hit a fast-moving projectile by firing another.

To realize a circuit of this type, PTB has developed a semiconductor chip upon which electron sources are integrated that can emit single electrons in a controlled fashion on a time scale of picoseconds; the chip also has detectors that can detect individual electrons. These components form building blocks for circuits in which individual electrons can be controlled that move ballistically and separately from all others. If one pair of electrons that have been generated from two separate sources cross paths within a collision region on the chip, their interaction will determine which electron reaches which of the different signal outputs. The simultaneous arrival of the electrons in the collision region (so-called coincidence) and the detection of each individual electron after passing through the circuit (the correlation of the detectors’ “clicks” in the signal outputs) give this coincidence correlation method a high level of precision and a high time resolution.

Although the electrons encounter each other only for a very short moment, PTB, in collaboration with the University of Latvia, has been able to demonstrate in this way that individual ballistic electrons can be manipulated to interact significantly on demand; the strength of this interaction allows different applications in the field of quantum technology to be realized. These include novel ultrafast electronic sensors and switches as well as the generation of quantum-mechanically entangled electronic states as carriers of quantum information for quantum computers.


Niels Ubbelohde
Department 2.5
Semiconductors and Magnetism
Phone: +49 531 592-2534
Opens local program for sending emailniels.ubbelohde(at)ptb.de

Scientific publication

N. Ubbelohde et al.: Two electrons interacting at a mesoscopic beam splitter. Nat. Nanotechnol. 18, 733 (2023).