  It has long been known that the lifetimes of superconducting qubits suffer
during readout, increasing readout errors. We show that this degradation is due
to the anti-Zeno effect, as readout-induced dephasing broadens the qubit so
that it overlaps 'hot spots' of strong dissipation, likely due to two-level
systems in the qubit's bath. Using a flux-tunable qubit to probe the qubit's
frequency dependent loss, we accurately predict the change in lifetime during
readout with a new self-consistent master equation that incorporates the
modification to qubit relaxation due to measurement-induced dephasing.
Moreover, we controllably demonstrate both the Zeno and anti-Zeno effects,
which explain suppression and the rarer enhancement of qubit lifetimes during
readout.
