  Both metaphysical and practical considerations related to time inversion have
intrigued scientists for generations. Physicists have strived to devise and
implement time-inversion protocols, in particular different forms of "time
mirrors" for classical waves. Here we propose an instantaneous time mirror for
quantum systems, i.e., a controlled time discontinuity generating wave function
echoes with high fidelities. This concept exploits coherent particle-hole
oscillations in a Dirac spectrum in order to achieve population reversal, and
can be implemented in systems such as (real or artificial) graphene.
