  We study a hybrid device defined in an InAs nanowire with an epitaxial Al
shell that consists of a quantum dot in contact with a superconducting island.
The device is electrically floating, prohibiting transport measurements, but
providing access to states that would otherwise be highly excited and unstable.
Radio-frequency reflectometry with lumped-element resonators couples
capacitatively to the quantum dot, and detects the presence of discrete subgap
states. We perform a detailed study of the case with no island states, but with
quantum-dot-induced subgap states controlled by the tunnel coupling. When the
gap to the quasi-continuum of the excited states is small, the capacitance
loading the resonator is strongly suppressed by thermal excitations, an effect
we dub "thermal screening". The resonance frequency shift and changes in the
quality factor at charge transitions can be accounted for using a single-level
Anderson impurity model. The established measurement method, as well as the
analysis and simulation framework, are applicable to more complex hybrid
devices such as Andreev molecules or Kitaev chains.
