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Equation 36 · The Bit Comes Back Before the Bearing

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g^\hat g

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g^\hat g

Symbol hat g

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For the compass, returned has to mean something else, because g is a continuous parameter and no channel can reproduce an unknown continuous value exactly. The honest promise is metrological: the same agent, using the same R∪\cup CtC_t , applies the best available measurement and estimator g^\hat g , and the achievable mean-squared error is bounded below by the quantum Cramér-Rao bound,

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