PT phase control in circular multi-core fibers.

We consider light dynamics in a circular multi-core fiber with balanced gain and loss core distribution, and show that transition from unbroken to broken PT phases can be conveniently controlled by geometric twist of the fiber. The twist introduces Peierls phases in the coupling constants and, thus, acts as an artificial gauge field. As an application, we discuss twist-induced tuning of optical transmission in a six-core fiber with one lossy core.