Abstract: When a quantum system is subjected to a quantum quench, its subsequent dynamics is governed by energy scales that become ever lower with increasing time: whereas the transient behavior right after the quench depends on high-energy excitations, the asymptotic long-time evolution is determined by low-lying excitations close to the final ground state. Thus, time- or frequency-resolved probes of the dynamics after a quantum quench offers insight into the nature of the system's eigenstates across the entire energy spectrum. We recently proposed  that such a quantum quench for the single-impurity Anderson Model can be induced by the sudden creation of an exciton in a quantum dot via optical absorption of an incident photon of definite frequency. The subsequent emergence of correlations between the spin degrees of freedom of the dot and a tunnel-coupled low-temperature Fermionic reservoir, ultimately leading to the Kondo effect, can be accurately mapped out through an optical absorption experiment. This experiment was recently carried out  with semiconductor quantum dots coupled to a degenerate electron gas, demonstrating experimentally for the first time the optical signature of Kondo correlations. I will discuss the theory behind the resulting lineshape that is found to unveil three very different dynamical regimes, corresponding to short, intermediate and long times after the initial excitation, which are in turn described by the three renormalization group fixed points of the Anderson Model. At low temperatures and just beyond the absorption threshold, the lineshape is dominated by a power-law singularity, with an exponent that is a universal function of magnetic field and gate voltage.
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