Simple pulses for universal quantum computation with a Heisenberg ABA B chain -: art. no. 054303

Recently, Levy has shown that quantum computation may be performed using an ABAB... chain of spin-1/2 systems with nearest-neighbor Heisenberg interactions. Levy notes that all necessary elementary Computational gates may be achieved purely by manipulating the spin-spin interaction: he proposes using.,spin-resonance techniques involving modulating the interaction strength at high frequency. Here, we establish an alternative: it is possible to perform the elementary gates via simple, nonoscillatory switching of the interaction strength. This approach removes a time bottle neck in Levy's scheme. so that all elementary operations may now be performed within a time scale of order (h) over bar/(E-A-E-B).