  Superconducting quantum processors have made significant progress in size and
computing potential. As a result, the practical cryogenic limitations of
operating large numbers of superconducting qubits are becoming a bottleneck for
further scaling. Due to the low thermal conductivity and the dense optical
multiplexing capacity of telecommunications fiber, converting qubit signal
processing to the optical domain using microwave-to-optics transduction would
significantly relax the strain on cryogenic space and thermal budgets. Here, we
demonstrate high-fidelity multi-shot optical readout through an optical fiber
of a superconducting transmon qubit connected via a coaxial cable to a fully
integrated piezo-optomechanical transducer. Using a demolition readout
technique, we achieve a multi-shot readout fidelity of >0.99 at 6 $\mu$W of
optical power transmitted into the cryostat with as few as 200 averages,
without the use of a quantum-limited amplifier. With improved frequency
matching between the transducer and the qubit readout resonator, we anticipate
that single-shot optical readout is achievable. Due to the small footprint
(<0.15mm$^2$) and the modular fiber-based architecture, this device platform
has the potential to scale towards use with thousands of qubits. Our results
illustrate the potential of piezo-optomechanical transduction for
low-dissipation operation of large quantum processors.
