Implementing quantum bits in silicon requires operations at low temperatures to preserve their quantum state as much as possible.  What about their control electronics? Operating these components at room temperature significantly limits the speed of signal processing.  It is therefore necessary to bring the control electronics as close as possible to the quantum device and to cool them as well.

The Grenoble researchers are providing proof of concept for such cryogenic CMOS (Complementary Metal Oxide Semiconductor) electronics, connected with silicon quantum dots, which, developed with the same technology, form the building blocks of silicon quantum bits.

They have integrated on the same FD-SOI substrate quantum dots and a CMOS current-to-voltage converter (transimpedance amplifier or TIA), capable of detecting the small current associated with the passage of single electrons (picoampere, 10^-12 A) through the quantum dots.

The TIA circuit operates at 10 mK, with only 1 μW of power consumption, thus avoiding heating of the cryostat. It has a linear response down to ± 40 nA with a bandwidth of 2.6 kHz that could be extended to about 200 kHz by optimizing its design.

In a more complete version, the chip integrates other analog and digital functions (multiplexer, buffer, signal amplifier, oscillator, level shifter) for current measurements with excitation in the GHz range.

These promising results open the way for dedicated cryogenic electronics in FD-SOI technology to improve the control and detection of quantum states (qubits) in a cryostat at very low temperatures.