  In this work, we show that in a four-quantum-dot ring, via introducing a
local Rashba spin-orbit interaction the spin bias in the transverse terminals
can be detected by observing the charge currents in the longitudinal probes. It
is found that due to the Rashba interaction, the quantum interference in this
system becomes spin-dependent and the opposite-spin currents induced by the
spin bias can present different magnitudes, so charge currents emerge. Besides,
the charge currents rely on both the magnitude and spin polarization direction
of the spin bias. It is believed that this method provides an electrical but
practical scheme to detect the spin bias (or the spin current).
