A quantum dot is a semiconductor nanostructure that is capable of confining electrons in a space with a characteristic size of a few dozen nanometers. This kind of artificial atom could be used as a quantum bit (or qubit).

Measuring this qubit requires an ultra-sensitive current sensor, such as a quantum point contact made by constriction of a conductor. However, this type of technology is difficult to extrapolate to dense qubit architectures. The integrability of these sensors is therefore an essential point for progress in the perspective of a future quantum computer. In this context, radiofrequency reflectometry appears to be a promising alternative.

The researchers from Inac used a metal-oxide semiconductor (MOS) double-gate silicon transistor at low temperature, comprising two quantum dots located below the two gate electrodes. They connected each of the gate electrodes to an individual radiofrequency resonator in order to probe the state of each quantum dot. Using a simultaneous reflectometry technique on both electrodes, they were able to measure the electronic transitions between the two quantum dots, in each dot and in the other transistor electrodes (drain and source contacts).

Multi-gate reflectometry on a larger scale should allow a single readout of quantum dot "strips".