[Perspective] Optical circulators reach the quantum level

Optical circuits for information processing offer higher data rates (channel capacities) and lower power consumption as compared with those of electronic circuits. Many optical devices (such as switches and isolators) have analogous electronic components (transistors and diodes), but some have special capabilities. For example, optical circulators form part of an unusual class of components known as nonreciprocal devices (1)—their optical properties depend on the direction of light passing thr