  Quantum multicritical points (QMCPs) emerge at the junction of two or more
quantum phase transitions due to the interplay of disparate fluctuations,
leading to novel universality classes. While quantum critical points have been
well characterized, our understanding of QMCPs is much more limited, even
though they might be less elusive to study experimentally than quantum critical
points. Here, we characterize the QMCP of an interacting heterogeneous quantum
system in two and three dimensions, the ferromagnetic random transverse-field
Ising model (RTIM). The QMCP of the RTIM emerges due to both geometric and
quantum fluctuations, studied here numerically by the strong disorder
renormalization group method. The QMCP of the RTIM is found to exhibit
ultraslow, activated dynamic scaling, governed by an infinite disorder fixed
point. This ensures that the obtained multicritical exponents tend to the exact
values at large scales, while also being universal -- i.e. independent of the
form of disorder -- , providing a solid theoretical basis for future
experiments.
