  We use microwave radiation generated by a semiconductor double quantum dot
(DQD) micromaser for charge state detection. A cavity is populated with n_c ~
6000 photons by driving a current through an emitter DQD. These photons are
used to sense the charge state of a target DQD that is located at the opposite
end of the cavity. Charge dynamics in the target DQD influence the output power
and emission frequency of the maser. Three different readout mechanisms are
compared. The detection scheme requires no cavity input field and may
potentially be used to improve the scalability of semiconductor and
superconducting qubit readout technologies.
