  We study the quantum transduction of a superconducting qubit to an optical
photon in electro-optomechanical and electro-optomagnonical systems. The
electro-optomechanical system comprises a flux-tunable transmon qubit coupled
to a suspended mechanical beam, which then couples to an optical cavity.
Similarly, in an electro-optomagnonical system, a flux-tunable transmon qubit
is coupled to an optical whispering gallery mode via a magnon excitation in a
YIG ferromagnetic sphere. In both systems, the transduction process is done in
sequence. In the first sequence, the qubit states are encoded in coherent
excitations of phonon/magnon modes through the phonon/magnon-qubit interaction,
which is non-demolition in the qubit part. We then measure the phonon/magnon
excitations, which reveal the qubit states, by counting the average number of
photons in the optical cavities. The measurement of the phonon/magnon
excitations can be performed at a regular intervals of time.

Quantum Physics