Coupling and entangling of quantum states in quantum dot molecules

We demonstrate coupling and entangling of quantum states in a pair of verti cally aligned, self-assembled quantum dots by studying the emission of an i nteracting electron-hole pair (exciton) in a single dot molecule as a funct ion of the separation between the dots. An interaction-induced energy split ting of the exciton is observed that exceeds 30 millielectron volts for a d ot layer separation of 4 nanometers. The results are interpreted by mapping the tunneling of a particle in a double dot to the problem of a single spi n. The electron-hole complex is shown to be equivalent to entangled states of two interacting spins.