Intrinsic spin fluctuations reveal the dynamical response function of   holes coupled to nuclear spin baths in (In,Ga)As quantum dots
  The problem of how single "central" spins interact with a nuclear spin bath is essential for understanding decoherence and relaxation in many quantum systems, yet is highly nontrivial owing to the many-body couplings involved. Different models yield widely varying timescales and dynamical responses (exponential, power-law, Gaussian, etc). Here we detect the small random fluctuations of central spins in thermal equilibrium (holes in singly-charged (In,Ga)As quantum dots) to reveal the timescales and functional form of bath-induced spin relaxation. This spin noise indicates long (400 ns) spin correlation times at zero magnetic field, that increase to $\sim$5 $\mu$s as hole-nuclear coupling is suppressed with small (100 G) applied fields. Concomitantly, the noise lineshape evolves from Lorentzian to power-law, indicating a crossover from exponential to inverse-log dynamics. 
Yan Li, N. Sinitsyn, D. L. Smith, D. Reuter, A. D. Wieck, D. R.   Yakovlev, M. Bayer, S. A. Crooker
cond-mat.mes-hall cond-mat.mtrl-sci