Simple pulses for universal quantum computation with a Heisenberg ABAB chain
Simon C. Benjamin · Physical Review A · 2001
Recently, Levy has shown that quantum computation may be performed using an $\mathrm{ABAB}\dots{}$ 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 $\ensuremath{\Elzxh}{/(E}_{A}\ensuremath{-}{E}_{B}).$