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 \emph{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.

17 pages, 8 figures; updated text, figures, supplemental material and references

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• Tomography via Correlation of Noisy Measurement Records
• Repetitive quantum non-demolition measurement and soft decoding of a silicon spin qubit
• Bayesian estimation for quantum sensing in the absence of single-shot detection
• Hamiltonian engineering for robust quantum state transfer and qubit readout in cavity QED
• Generalized figure of merit for qubit readout
• Maximizing the purity of a qubit evolving in an anisotropic environment
• Flying-cat parity checks for quantum error correction
• Spin-qubit readout analysis based on a hidden Markov model
• Four-state discrimination for a pair of spin qubits via gate reflectometry
• Multi-shot readout error benchmark of the nitrogen-vacancy center's electronic qubit