Title: Holography and thermalization in optical pump-probe spectroscopy,
Abstract: Using holography, we model experiments in which a 2+1D strange metal is
pumped by a laser pulse into a highly excited state, after which the time
evolution of the optical conductivity is probed. We consider a finite-density
state with mildly broken translation invariance and excite it by oscillating
electric field pulses. At zero density, the optical conductivity would assume
its thermalized value immediately after the pumping has ended. At finite
density, pulses with significant DC components give rise to slow exponential
relaxation, governed by a vector quasinormal mode. In contrast, for
high-frequency pulses the amplitude of the quasinormal mode is strongly
suppressed, so that the optical conductivity assumes its thermalized value
effectively instantaneously. This surprising prediction may provide a stimulus
for taking up the challenge to realize these experiments in the laboratory.
Such experiments would test a crucial open question faced by applied
holography: Are its predictions artefacts of the large $N$ limit or do they
enjoy sufficient UV independence to hold at least qualitatively in real-world
systems?