  Einstein-Podolsky-Rosen (EPR) steering is a type of quantum correlation which
allows one to remotely prepare, or steer, the state of a distant quantum
system. While EPR steering can be thought of as a purely spatial correlation
there does exist a temporal analogue, in the form of single-system temporal
steering. However, a precise quantification of such temporal steering has been
lacking. Here we show that it can be measured, via semidefinite programming,
with a temporal steerable weight, in direct analogy to the recently proposed
EPR steerable weight. We find a useful property of the temporal steerable
weight in that it is a non-increasing function under completely-positive
trace-preserving maps and can be used to define a sufficient and practical
measure of strong non-Markovianity.
