The diffusion of defects in crystalline materials governs macroscopic behaviour in a wide range of processes, including alloying, precipitation, phase transformation, and creep. In real materials, intrinsic defects are unavoidably bound to static trapping centres such as impurity atoms, meaning that their diffusion is controlled by the de-trapping process. It is generally held that de-trapping occurs only by thermal activation. In this Letter we report the first direct observation of the quantum de-trapping of defects below around 1/3 of the Debye temperature. We successfully monitored the de-trapping and migration of self-interstitial atom clusters, strongly trapped by impurity atoms in tungsten, by triggering de-trapping out of equilibrium at cryogenic temperatures, using high-energy electron irradiation and in-situ transmission electron microscopy. The quantum-assisted de-trapping leads to low temperature diffusion rates orders of magnitude higher than a naive classical estimate suggests. Our analysis shows that this phenomenon is generic to any crystalline material.