= Amplitude damping channel
{title2=$A_0=|0\rangle\langle0|+\sqrt{1-p}|1\rangle\langle1|,\quad A_1=\sqrt p|0\rangle\langle1|$}
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A zero-temperature energy-relaxation channel transfers the excited population of a <qubit> to its ground state. Its <Kraus operators> are $A_0=\operatorname{diag}(1,\sqrt{1-p})$ and $A_1=\sqrt p|0\rangle\langle1|$ for $0\leq p\leq1$. They satisfy $\sum_jA_j^\dagger A_j=I$. The excited population is multiplied by $1-p$ and coherences by $\sqrt{1-p}$. For nonzero $p$, it is not a <unital quantum channel>.
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