  When two qubits A and B are in an appropriate state, Alice can remotely steer
Bob's system B into different ensembles by making different measurements on A.
This famous phenomenon is known as quantum steering, or Einstein-Podolsky-Rosen
steering. Importantly, quantum steering establishes the correspondence not only
between a measurement on A (made by Alice) and an ensemble of B (owned by Bob)
but also between each of Alice's measurement outcomes and an unnormalized
conditional state of Bob's system. The unnormalized conditional states of B
corresponding to all possible measurement outcomes of Alice are called Alice's
steering outcomes. We show that, surprisingly, the $4$-dimensional geometry of
Alice's steering outcomes completely determines both the non-separability of
the two-qubit state and its steerability from her side. Consequently, the
problem of classifying two-qubit states into non-separable and steerable
classes is equivalent to geometrically classifying certain $4$-dimensional
skewed double-cones.
