  The interaction-free measurement is a fundamental quantum effect whereby the
presence of a photosensitive object is determined without irreversible photon
absorption. Here we propose the concept of coherent interaction-free detection
and demonstrate it experimentally using a three-level superconducting transmon
circuit. In contrast to standard interaction-free measurement setups, where the
dynamics involves a series of projection operations, our protocol employs a
fully coherent evolution that results, surprisingly, in a higher probability of
success. We show that it is possible to ascertain the presence of a microwave
pulse resonant with the second transition of the transmon, while at the same
time avoid exciting the device onto the third level. Experimentally, this is
done by using a series of Ramsey microwave pulses coupled into the first
transition and monitoring the ground-state population.
