Decomposable positive map
= Decomposable positive map
A decomposable positive map between complex matrix algebras has the form $\Phi=\Phi_1+\Phi_2\circ T$, where $\Phi_1,\Phi_2$ are <completely positive maps> and $T$ is the <matrix transpose>. Such a map cannot detect a <positive partial transpose> entangled state: applying it to one subsystem gives a sum of two positive operators.