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Improving quantum state detection with adaptive sequential observations



Emanuel Knill, Scott Glancy, Daniel Cole, Shawn Geller


For many quantum systems intended for information processing, one detects the logical state of a qubit by integrating a continuously observed quantity over time. For example, ion and atom qubits are typically measured by driving a cycling transition and counting the number of photons observed from the resulting fluorescence. Instead of recording only the total observed count, one can observe the photon arrival times and get a state detection advantage by using the temporal structure in a model such as a Hidden Markov Model. We initiate the study of what further advantage may be achieved by applying pulses to adaptively transform the state during the observation. We give a three-state example where adaptively chosen transformations yield a clear advantage, and we compare performances on a prototypical ion example, where we see improvements in some regimes. We make available a software package that can be used for exploration of temporally resolved strategies with and without adaptively chosen transformations.
Quantum Science and Technology


quantum bit measurement, hidden Markov models


Knill, E. , Glancy, S. , Cole, D. and Geller, S. (2022), Improving quantum state detection with adaptive sequential observations, Quantum Science and Technology, [online],, (Accessed May 21, 2024)


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Created May 13, 2022, Updated June 7, 2023