  Quantum dots are arguably the best interface between matter spin qubits and
flying photonic qubits. Using quantum dot devices to produce joint
spin-photonic states requires the electronic spin qubits to be stored for
extended times. Therefore, the study of the coherence of spins of various
quantum dot confined charge carriers is important both scientifically and
technologically. In this study we report on spin relaxation measurements
performed on five different forms of electronic spin qubits confined in the
very same quantum dot. In particular, we use all optical techniques to measure
the spin relaxation of the confined heavy hole and that of the dark exciton - a
long lived electron-heavy hole pair with parallel spins. Our measured results
for the spin relaxation of the electron, the heavy-hole, the dark exciton, the
negative and the positive trions, in the absence of externally applied magnetic
field, are in agreement with a central spin theory which attributes the
dephasing of the carriers' spin to their hyperfine interactions with the
nuclear spins of the atoms forming the quantum dots. We demonstrate that the
heavy hole dephases much slower than the electron. We also show, both
experimentally and theoretically, that the dark exciton dephases slower than
the heavy hole, due to the electron-hole exchange interaction, which partially
protects its spin state from dephasing.
