  Chiral spin pumping is the generation of a unidirectional spin current in
half of ferromagnetic films or conductors by dynamic dipolar stray fields from
close-by nanomagnets. We formulate a general theory of long-range chiral
interactions between magnets mediated by unidirectional traveling waves, e.g.,
spin waves in a magnetic film or microwaves in a waveguide. The traveling waves
emitted by an excited magnet can be perfectly trapped by a second, initially
passive, magnet by a dynamical interference effect. When both magnets are
excited by a uniform microwave, the chiral interaction between them creates a
large imbalance in their magnon numbers.
