Figure 2
From: Discrimination of two-qubit unitaries via local operations and classical communication
A convex hull in Eq. (11) of the spectrum of a unitary transformation is shown.
Vertices A, B, C and D correspond to 
, 
, 
and 
, respectively, since λ4 ≥ λ1 ≥ λ2 ≥ λ3. In (a), the local convex hull is constructed as □PQRS where {P, Q, R, S} are midpoints of {DA, AB, BC, CD} respectively. In (b), it is shown that for any of {P, Q, R, S} if a line orthogonal to {DA, AB, BC, CD} is drawn, it passes through the origin. It means that if 
, then it also holds true that 
.
