Symbol A

Its job in the formula

A is a part of this expression. Its role is fixed by the surrounding article and by the operations shown in the formula.

Where the article explains it

For the qubit, returned means: there exists a recovery channel $\mathcal R$ , built from quantum operations an agent holding both the full early radiation R and a further batch of radiation $C_t$ collected up to time t can actually perform, whose entanglement fidelity to the identity channel on A is within $\epsilon$ of perfect,

Learn the underlying idea

A variable is a named place for a value. Its letter is a local label: x can mean position in one formula and a data point in another.

Open the illustrated variables: a letter stands for a value guide →