  Spectroscopic and interferometric measurements complement each other in
extracting the fundamental properties of quantum many-body systems. While
spectroscopy provides precise measurements of equilibrated energies,
interferometry can elucidate the dynamical evolution of the system. For an
impurity immersed in a bosonic medium, both are equally important for
understanding the quasiparticle physics of the Bose polaron. Here, we compare
the interferometric and spectroscopic timescales to the underlying dynamical
regimes of the impurity dynamics and the polaron lifetime, highlighting the
capability of the interferometric approach to clearly resolve polaron dynamics.
In particular, interferometric measurements of the coherence amplitude at
strong interactions reveal faster quantum dynamics at large repulsive
interaction strengths than at unitarity. These observations are in excellent
agreement with a short-time theoretical prediction including both the continuum
and the attractive polaron branch. For longer times, qualitative agreement with
a many-body theoretical prediction which includes both branches is obtained.
Moreover, the polaron energy is extracted from interferometric measurements of
the observed phase velocity in agreement with previous spectroscopic results
from weak to strong attractive interactions. Finally, the phase evolution
allows for the measurement of an energetic equilibration timescale, describing
the initial approach of the phase velocity to the polaron energy.
Theoretically, this is shown to lie within the regime of universal dynamics
revealing a fast initial evolution towards the formation of polarons. Our
results give a comprehensive picture of the many-body physics governing the
Bose polaron and thus validates the quasiparticle framework for further
studies.
