  Many physical implementations of qubits---including ion traps, optical
lattices and linear optics---suffer from loss. A nonzero probability of
irretrievably losing a qubit can be a substantial obstacle to fault-tolerant
methods of processing quantum information, requiring new techniques to
safeguard against loss that introduce an additional overhead that depends upon
the loss rate. Here we present a scalable and platform-independent protocol for
estimating the average loss rate (averaged over all input states) resulting
from an arbitrary Markovian noise process, as well as an independent estimate
of detector efficiency. Moreover, we show that our protocol gives an additional
constraint on estimated parameters from randomized benchmarking that improves
the reliability of the estimated error rate and provides a new indicator for
non-Markovian signatures in the experimental data. We also derive a bound for
the state-dependent loss rate in terms of the average loss rate.
