Coherent dynamics of coupled electron and hole spins in semiconductors

We observe the coherent dynamics of coupled electron and hole spins within 2D-excitons. The dynamics are induced by the exchange interaction of electron and hole and by an external magnetic field tilted from the plane of a 3 nm GaAs/(AlGa)As quantum well. The observed quantum beats are well described by a Schrِdinger equation for the pair of spins in a magnetic field which is solved analytically. The results lead to a controlled not (CNOT) gate, a key element in quantum computation, realized with semiconductor nanostructures.