  Although geometric phases in quantum evolution were historically overlooked,
their active control now stimulates strategies for constructing robust quantum
technologies. Here, we demonstrate arbitrary single-qubit holonomic gates from
a single cycle of non-adiabatic evolution, eliminating the need to concatenate
two separate cycles. Our method varies the amplitude, phase, and detuning of a
two-tone optical field to control the non-Abelian geometric phase acquired by a
nitrogen-vacancy center in diamond over a coherent excitation cycle. We
demonstrate the enhanced robustness of detuned gates to excited-state
decoherence and provide insights for optimizing fast holonomic control in
dissipative quantum systems.
