… Abstract: We perform dispersive readout of a superconducting qubit using optical heterodyne
detection via a mechanical electro-optic transducer, without causing significant backaction
on the qubit. This is a key milestone in linking remote superconducting quantum processors. …
We show that the qubit dephasing rate is minimally affected by the operation of the
transducer: it imparts backaction equivalent to that of an additional An = (3±1)×10−3 photons
occupying the microwave readout cavity that is dispersively coupled to the transmon …