117 citations · 207 across the 16 of their papers we have counts for
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An attainable Gill-Massar-type bound for spin-factor models
Koichi Yamagata
We determine the exact local precision limits for single-copy estimation of smooth multiparameter quantum statistical models contained in spin factors, a class of matrix Jordan alg…
Bayesian Gill-Massar Bound: An Attainable Lower Bound for Qubit Parameter Estimation
Ke-Han Zhao, Koichi Yamagata, Jun Suzuki
We study lower bounds for Bayesian quantum parameter estimation, with a particular focus on qubit models. While several lower bounds on the Bayes risk have been proposed, including…
Bayesian Monotone Metrics for Multiparameter Quantum Estimation
Jianchao Zhang, Koichi Yamagata, Jun Suzuki
Bayesian quantum estimation offers a finite-data framework for quantum sensing and metrology, yet a unified geometric formulation for multiparameter Bayes risk has been lacking. We…
Quantum Sufficiency for Self-Adjoint Statistical Models via Likelihood-Type Operators on Real -Subalgebras and Real Jordan Algebras
Koichi Yamagata
We develop a theory of quantum sufficiency on real *-subalgebras and real Jordan algebras for models consisting of general self-adjoint operators, including derivatives of states.…
Sufficient support size of measurements for quantum estimation
Koichi Yamagata
In quantum estimation for a -parameter family of density operators on a finite-dimensional Hilbert space , an estimator is specified by a pair $\left(M,\hatθ\right)…
A game-theoretic probability approach to loopholes in CHSH experiments
Takara Nomura, Koichi Yamagata, Akio Fujiwara
We study the CHSH inequality from an informational, timing-sensitive viewpoint using game-theoretic probability, which avoids assuming an underlying probability space. The locality…