Sommaire:

The evolution of quantum systems is characterised by the interference of coherent amplitudes associated with single or many-particle paths. By fixing the phase relation between these amplitudes, symmetries of the system fashion the resulting dynamics. I will briefly mention two examples where the exchange symmetry between identical particles plays an important role: totally destructive many-particle interference and dynamics of partially distinguishable bosons. I will then focus on a single-particle problem inspired by energy transport in biological photosynthetic complexes: the transfer of an excitation across a random network of two-level systems. Symmetry of the Hamiltonian under reflection is known to favour efficient transport despite the disordered nature of the system. However, this is incompatible with the large detuning of excitation energies observed in biological systems, where coupling to vibrational degrees of freedom is necessary to bridge the energy gap. We therefore consider periodically driven random networks and show that a generalised symmetry on Floquet-Hilbert space leads to an enhancement of the transfer probability.

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