  We present a scheme designed to suppress the dominant source of infidelity in
entangling gates between quantum systems coupled through intermediate bosonic
oscillator modes. Such systems are particularly susceptible to residual
qubit-oscillator entanglement at the conclusion of a gate period which reduces
the fidelity of the target entangling operation. We demonstrate how the
exclusive use of discrete phase shifts in the field moderating the
qubit-oscillator interaction - easily implemented with modern synthesizers - is
sufficient to both ensure multiple oscillator modes are decoupled and to
suppress the effects of fluctuations in the driving field. This approach is
amenable to a wide variety of technical implementations including geometric
phase gates in superconducting qubits and the Molmer-Sorensen gate for trapped
ions. We present detailed example protocols tailored to trapped-ion experiments
and demonstrate that our approach allows multiqubit gate implementation with a
significant reduction in technical complexity relative to previously
demonstrated protocols.
