  Quantum computers require interfaces with classical electronics for efficient
qubit control, measurement and fast data processing. Fabricating the qubit and
the classical control layer using the same technology is appealing because it
will facilitate the integration process, improving feedback speeds and offer
potential solutions to wiring and layout challenges. Integrating classical and
quantum devices monolithically, using complementary metal-oxide-transistor
(CMOS) processes, enables the processor to profit from the most mature
industrial technology for the fabrication of large scale circuits. Here we
demonstrate the integration of a single-electron charge storage CMOS quantum
dot with a CMOS transistor for control of the readout via gate-based dispersive
sensing using a lumped element $LC$ resonator. The control field-effect
transistor (FET) and quantum dot are fabricated on the same chip using
fully-depleted silicon-on-insulator technology. We obtain a charge sensitivity
of $\delta q=165\, \mu e \mathrm{Hz}^{-1/2}$ when the quantum dot readout is
enabled by the control FET. Additionally, we observe a single-electron
retention time of the order of a second when storing a single-electron charge
on the quantum dot at milli-Kelvin temperatures. These results demonstrate
first steps towards time-based multiplexing of gate-based dispersive qubit
readout in CMOS technology opening the path for the development of an
all-silicon quantum-classical processor.
