Broken symmetry and quantum entanglement of an exciton inInxGa1−xAs∕GaAsquantum dot molecules

Abstract

The ability of a quantum dot to confine photogenerated electron-hole pairs created interest in the behavior of such an exciton in a ``dot molecule,'' being a possible register in quantum computing. When two quantum dots are brought close together, the quantum state of the exciton may extend across both dots. The exciton wave function in such a dot molecule may exhibit entanglement. Atomistic pseudopotential calculations of the wave function for an electron-hole pair in a dot molecule made of two identical ${\mathrm{In}}_{x}{\mathrm{Ga}}_{1\ensuremath{-}x}\mathrm{As}∕\mathrm{Ga}\mathrm{As}$ dots reveal that the common assumption of single-particle wave functions forming bonding and antibonding states is erroneous. The true behavior of single-particle electrons and holes leads to symmetry-broken excitonic two-particle wave functions, dramatically suppressing entanglement. We find that at large interdot separations, the exciton states are built from heteronuclear single-particle states while at small interdot separations the exciton is derived from heteronuclear hole states and homonuclear electron states. We calculate the entanglement of the excitons and find a maximum value of 80% at an interdot separation of $8.5\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$ and very small values for larger and smaller distances.