Feasibility study of the quantum XOR gate based on coupled asymmetric semiconductor quantum dots

We propose an implementation of the quantum XOR (controlled-NOT) gate on th e basis of coupled asymmetric quantum dots. Results of our numerical simula tions show that the coupling constant of the dipole-dipole interaction and the probability of spontaneous emission can be tuned over a wide range by a proper choice of the potential profile, material parameters, and distances between the dots. We argue that the use of the asymmetric potential profil e provides better conditions for having the Ising-type interaction between the dots than earlier proposed schemes based on regular symmetric quantum d ots biased with an electric field. Our system gives better resolution of di fferent quantum states, avoids any undesirable time evolution of these stat es, and can be driven with a femtosecond laser. The qubit manipulation and time coherency requirements are also discussed. (C) 1999 Academic Press.