Markov chain Monte Carlo detector tomography applied to a NbTiN nanobridge

We demonstrate the use of a flexible and highly accurate Markov chain Monte Carlo quantum detector tomography method as a minimization algorithm to best describe the response of an efficient 120 nm wide NbTiN superconducting nanobridge single photon detector. Separation of the internal quantum efficiency and external quantum efficiency is possible due to the difference in saturation behavior of an ideal one-photon threshold detector as compared to a detector with non-unity one-photon internal quantum efficiency. From a statistical analysis of our measurements (at T=(4.23 ± 0.01) K, I=(29.4 ± 0.1) μA, I/Iswitch=(0.90 ± 0.01)), we find an external quantum efficiency of η=(1.60 ± 0.05)×10−6, a one-photon internal quantum efficiency of p1=0.568 ± 0.008, and a unity multi-photon (two or more) internal quantum efficiency.