In this study, we evidence hole spin mode locking in a largely inhomogeneous p-doped InAs quantum dot (QD) ensemble, g h x /g h x ≈ 34%, which allows us to reveal a long spin coherence time of T h 2 ≈ 0.8 μs. In addition, with a two-pump experiment, we demonstrate, in a low magnetic range 60-120 mT, the possibility to synchronize and tune a single subset of QDs through the distribution. Experiments are supported by an analysis within the density matrix approach.The resident spin of a carrier confined in a quantum dot (QD) is a promising candidate for quantum information systems. Until recently, most theoretical and experimental studies have been centered on the electron spin, and have demonstrated that the ultimate limitation, at low temperature and zero magnetic field, is the hyperfine interaction of an electron with a nuclear-spin ensemble. Due to the limited number of QD nuclei interacting with the electron spin, on the order of 10 5 , random fluctuations of the nuclearspin bath lead to a dephasing time on the order of ns for InAs QDs. Recently, the initialization of hole spin has been demonstrated, 1-7 and it has emerged as a more attractive candidate, with a one-order-of-magnitude weaker hyperfine coupling. 4,[8][9][10][11][12] Several studies have reported a long hole spin relaxation time T h 1 , from μs to ms, under different conditions of temperature and magnetic field. 1,13-16 In early single-hole experiments of coherent population trapping, the hole spin coherence time was estimated to be larger than 100 ns. 17 In more recent experiments in time domain, the hole-spin coherence time has been found to be 20 ns, but these single hole-spin measurements were affected by electrical-noise 18,19 or nuclear-spin 20 fluctuations. Recent spin-echo experiments allow to circumvent the inhomogeneous decoherence and measure a much longer hole-spin coherence time T h 2 , in the microsecond range between 6 and 10 T. 18 This value is of the same order of magnitude as for electrons 21 and represents an upper bound on the free-induction decay time of hole spin coherence. 22 For electron spins, the possibility to go beyond the ensemble inhomogeneities and to measure a long coherence time by using a periodic train of circularly polarized pulses has been demonstrated. A single pulse creates an ensemble of electron spins along its propagation direction and perpendicular to an external magnetic field (Voigt geometry). Each electron spin precesses about the field and, due to the inhomogeneity of the precession frequencies, the phase coherence is quickly lost. The train of pulses allows the phase synchronization of subsets of the whole spin ensemble, for which the precession frequency is a multiple of the laser repetition rate. This effect was called "electron spin mode locking." 23,24 It has allowed the measurement of an electron spin coherence time of 600 ns at 2 T, 25 and 3 μs at 6 T, 23 in an ensemble of InGaAs QDs with a relative dispersion of the in-plane electron Landé factor g e x /g e x ≈ 1%.Holes are more sensitive than...