Coherence-Sensitive Readout Models for Quantum Devices: Beyond the Classical Assignment Matrix

• URL: http://arxiv.org/abs/2512.13949v1
• Date: Mon, 15 Dec 2025 23:04:33 GMT
• Title: Coherence-Sensitive Readout Models for Quantum Devices: Beyond the Classical Assignment Matrix
• Authors: Zachariah Malik, Zain Saleem,
• Abstract summary: Readout error models for noisy quantum devices almost universally assume that measurement noise is classical.<n>This work provides a natural, fully general framework for coherence-sensitive readout modeling on current and future quantum devices.
• Score: 0.0
• License: http://creativecommons.org/licenses/by/4.0/
• Abstract: Readout error models for noisy quantum devices almost universally assume that measurement noise is classical: the measurement statistics are obtained from the ideal computational-basis populations by a column-stochastic assignment matrix $A$. This description is equivalent to assuming that the effective positive-operator-valued measurement (POVM) is diagonal in the measurement basis, and therefore completely insensitive to quantum coherences. We relax this assumption and derive a fully general expression for the observed measurement probabilities under arbitrary completely positive trace-preserving (CPTP) noise preceding a computational-basis measurement. Writing the ideal post-circuit stat $\tildeρ$ in terms of its populations $x$ and coherences $y$, we show that the observed probability vector $z$ satisfies $z = A x + C y$, where $A$ is the familiar classical assignment matrix and $C$ is a coherence-response matrix constructed from the off-diagonal matrix elements of the effective POVM in the computational basis. The classical model $z = A x$ arises if and only if all POVM elements are diagonal; in this sense $C$ quantifies accessible information about coherent readout distortions and interference between computational-basis states, all of which are invisible to models that retain only $A$. This work therefore provides a natural, fully general framework for coherence-sensitive readout modeling on current and future quantum devices.

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