LAUSR

Unitary control changes the absorption and emission of an object by transforming the external light modes. It is widely used and underlies coherent perfect absorption. Yet two basic questions remain unanswered: For a given object under unitary control, what absorptivity α, emissivity e, and their contrast δ=e-α are attainable? How to obtain a given α, e, or δ? We answer both questions using the mathematics of majorization. We show that unitary control can achieve perfect violation or preservation of Kirchhoff's law in nonreciprocal objects, and uniform absorption or emission for any object.