  We propose a protocol to realize quantum simulation and computation in spin
systems with long-range interactions. Our approach relies on the local
addressing of single spins with external fields parametrized by Walsh
functions. This enables a mapping from a class of target Hamiltonians, defined
by the graph structure of their interactions, to pulse sequences. We then
obtain a recipe to implement arbitrary two-body Hamiltonians and universal
quantum circuits. Performance guarantees are provided in terms of bounds on
Trotter errors and total number of pulses. Additionally, Walsh pulse sequences
are shown to be robust against various types of pulse errors, in contrast to
previous hybrid digital-analog schemes of quantum computation. We demonstrate
and numerically benchmark our protocol with examples from the dynamics of spin
models, quantum error correction and quantum optimization algorithms.
