Quantum device and method for producing the same

A quantum device comprising a transistor pattern carried by a substrate, the transistor pattern comprising, in a stack stacked in a stacking direction:

• a gate dielectric on a front face of the substrate, and
• a superconducting gate on a top face of the gate dielectric, the superconducting gate having a base face in contact with the top face of the gate dielectric, a top face opposite the base face and sidewalls extending between the base face and the top face of the superconducting gate, the superconducting gate comprising at least one superconducting region made of a metal material based on at least one superconducting element, the superconducting gate having a diffusion front of the at least one superconducting element oriented in the stacking direction, wherein
• the superconducting gate comprises a basal portion and a top portion, the basal portion extending in the stacking direction from the base face to the top portion and the top portion extending in the stacking direction from the basal portion to the top face of the superconducting gate, the basal portion having a first dimension, taken in a first direction of a basal plane parallel to the base face, the first dimension being smaller than a second dimension of the top portion, taken in the first direction, and the first dimension being smaller than a third dimension of the top face of the gate dielectric, taken in the first direction,
• the basal portion is recessed with respect to the top portion and to the gate dielectric in the first direction, the recess forming at least one cavity, and
• the transistor pattern further comprises a dielectric portion made of a dielectric material in the at least one cavity.