  An experimental technique for the indirect manipulation and detection of
electron spins entangled in two-dimensional magnetoexcitons has been developed.
The kinetics of the spin relaxation has been investigated. Photoexcited
spin-magnetoexcitons were found to exhibit extremely slow relaxation in
specific quantum Hall systems, fabricated in high mobility GaAs/AlGaAs
structures, namely, the relaxation time reaches values over one hundred
microseconds. A qualitative explanation of this spin-relaxation kinetics is
presented. Its temperature and magnetic field dependencies are discussed within
the available theoretical framework.
