  The quantum anomalous Hall (QAH) effect is characterized by a dissipationless
chiral edge state with a quantized Hall resistance at zero magnetic field.
Manipulating the QAH state is of great importance in both the understanding of
topological quantum physics and the implementation of dissipationless
electronics. Here, we realized the QAH effect in the magnetic topological
insulator Cr-doped (Bi,Sb)2Te3 (CBST) grown on an uncompensated
antiferromagnetic insulator Al-doped Cr2O3. Through polarized neutron
reflectometry (PNR), we find a strong exchange coupling between CBST and
Al-Cr2O3 surface spins fixing interfacial magnetic moments perpendicular to the
film plane. The interfacial coupling results in an exchange-biased QAH effect.
We further demonstrate that the magnitude and sign of the exchange bias can be
effectively controlled using a field training process to set the magnetization
of the Al-Cr2O3 layer. Our work demonstrates the use of the exchange bias
effect to effectively manipulate the QAH state, opening new possibilities in
QAH-based spintronics.
