Spin mixing of two electrons in a quantum dot

The optical initialization and readout of an electron spin in a quantum dot involves often the lowest excited states of two electrons in a negative trion. The dynamics involves mixing of electron triplets and excited singlets. Typically, the mixing mechanism invoked has been electron-hole exchange in the presence of dot lateral asymmetries, but this has not been always consistent with the observed dephasing rates. We describe here a more general and stronger singlet-triplet mixing mechanism that does not require dot asymmetry.