  The quantum anomalous Hall (QAH) insulator is a topological quantum state
with quantized Hall resistance and zero longitudinal resistance in the absence
of an external magnetic field. The QAH insulator carries spin-polarized
dissipation-free chiral edge current and thus provides a unique opportunity to
develop energy-efficient transformative information technology. Despite
promising advances on the QAH effect over the past decade, the QAH insulator
has thus far eluded any practical applications. In addition to its low working
temperature, the QAH state in magnetically doped topological insulator (TI)
films/heterostructures usually deteriorates with time in ambient conditions. In
this work, we prepare three QAH devices with similar initial properties and
store them in different environments to investigate the evolution of their
transport properties. The QAH device without a protection layer in air show
clear degradation and becomes hole-doped with the charge neutral point shifting
significantly to positive gate voltages. The QAH device kept in an argon glove
box without a protection layer shows no measurable degradation after 560 hours
and the device protected by a 3 nm AlOx protection layer in air shows minimal
degradation with stable QAH properties. Our work shows a route to preserve the
dissipation-free chiral edge state in QAH devices for potential applications in
quantum information technology.
