title: Soft decoding of a qubit readout apparatus.
abstract: Qubit readout is commonly performed by thresholding a collection of analog detector signals to obtain a sequence of single-shot bit values. The intrinsic irreversibility of the mapping from analog to digital signals discards soft information associated with an a posteriori confidence that can be assigned to each bit value when a detector is well characterized. Accounting for soft information, we show significant improvements in enhanced state detection with the quantum repetition code as well as quantum state or parameter estimation. These advantages persist in spite of non-Gaussian features of realistic readout models, experimentally relevant small numbers of qubits, and finite encoding errors. These results show useful and achievable advantages for a wide range of current experiments on quantum state tomography, parameter estimation, and qubit readout.
authors.affiliation: Department of Physics, McGill University, Montreal, Quebec H3A 2T8, Canada.
authors.forename: B
authors.initials: B
authors.lastname: D'Anjou
authors.affiliation: Department of Physics, McGill University, Montreal, Quebec H3A 2T8, Canada and Canadian Institute for Advanced Research, Toronto, Ontario M5G 1Z8, Canada.
authors.forename: W A
authors.initials: WA
authors.lastname: Coish