Evaluation of hole-spin superposition in GaAs/AlGaAs quantum wells through time-resolved photoluminescence measurements

Relaxation dynamics of the up–down superposition of hole spins in undoped GaAs/AlGaAs quantum wells were investigated by means of time-resolved photoluminescence (PL) measurements with a view toward achieving quantum bits using hole spins. Linearly polarized PL signals reflecting the hole-spin superposition were observed using linearly polarized excitation light under quasi-resonant excitation conditions. In contrast to circular-polarization experiments conducted under nonresonant excitation conditions, the decay time of the degree of linear polarization obtained from the time-resolved PL signal increased slightly with increasing quantum confinement energy. These experimental results demonstrate that the creation and observation of hole-spin superposition under resonant conditions are crucial for manipulating hole-spin quantum bits.