How to combine three quantum states

Understand

We devise a ternary operation for combining three quantum states: it consists of permuting the input systems in a continuous fashion and then discarding all but one of them.

• This generalizes a binary operation recently studied by Audenaert et al.
• [arXiv:1503.04213] in the context of entropy power inequalities.
• Our ternary operation continuously interpolates between all such nested binary operations.