Leakage RB

One significant source of error in CR gates, especially when minimizing gate time, is leakage of the quantum state out of the computational subspace, in particular to the second excited state of the control transmon. We have observed and characterized this leakage channel during the CR gate by monitoring directly the second excited states of the transmons, denoted |2>. 

To quantify leakage of the CR gate, we monitor the |2>-state while performing two-qubit randomized benchmarking experiments. The exponential decay observed is a measure of the leakage.