  Relaxation and dephasing of hole spins are measured in a gate-defined Ge/Si
nanowire double quantum dot using a fast pulsed-gate method and dispersive
readout. An inhomogeneous dephasing time $T_2^* \sim 0.18~\mathrm{\mu s}$
exceeds corresponding measurements in III-V semiconductors by more than an
order of magnitude, as expected for predominately nuclear-spin-free materials.
Dephasing is observed to be exponential in time, indicating the presence of a
broadband noise source, rather than Gaussian, previously seen in systems with
nuclear-spin-dominated dephasing.
