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 interac tions. Levy notes that all necessary elementary Computational "gates" may b e achieved purely by manipulating the spin-spin interaction: he proposes us ing.,spin-resonance" techniques involving modulating the interaction streng th at high frequency. Here, we establish an alternative: it is possible to perform the elementary gates via simple, nonoscillatory switching of the in teraction strength. This approach removes a time "bottle neck" in Levy's sc heme. so that all elementary operations may now be performed within a time scale of order (h) over bar/(E-A-E-B).