Decoherence originates from the leakage of quantum information into external
degrees of freedom. For a qubit the two main decoherence channels are
relaxation and dephasing. Here, we report an experiment on a superconducting
qubit where we retrieve part of the lost information in both of these channels.
We demonstrate that raw averaging the corresponding measurement records
provides a full quantum tomography of the qubit state where all three
components of the effective spin-1/2 are simultaneously measured. From single
realizations of the experiment, it is possible to infer the quantum
trajectories followed by the qubit state conditioned on relaxation and/or
dephasing channels. The incompatibility between these quantum measurements of
the qubit leads to observable consequences in the statistics of quantum states.
The high level of controllability of superconducting circuits enables us to
explore many regimes from the Zeno effect to underdamped Rabi oscillations
depending on the relative strengths of driving, dephasing and relaxation.Comment: Supplemental videos can be found at
http://physinfo.fr/publications/Ficheux1710.html and supplemental information
can be found as an ancillary file on arxi