Gate voltage control of exchange interaction for phosphorous donors in silicon.*

We perform realistic calculations for coupled phospherous donors in silicon delta-doping sheet, which is relevant for silicon-based quantum computation. With the help of generalized unrestricted Hartree-Fock method, we study the influence of valley-orbit interaction on the exchange coupling. We also solve the tunable gate potential by Poisson's equation and study the gate votage dependence of the exchange splitting. The implications are examined for silicon-based quantum computer architecture, where phospherous donor electron spin encodes logic qubit and exchange interaction is employed to generate entanglement among qubits.