Phasonic Spectroscopy of Tunable Cold-Atom Quasicrystals*

We describe and demonstrate a new spectroscopic probe of tunable quantum quasicrystals, realized with cold atoms in a quasiperiodic optical lattice. The formation, stability, excitation, and electronic structure of quasicrystals remain incompletely understood. In particular, phasonic modes (a quasicrystalline analogue of phonon modes) have important but poorly-understood effects on thermal and electronic transport in real quasicrystals. The extreme tunability of cold-atom experiments enables a new technique for investigation of these open questions: coherent phasonic spectroscopy of tunable quantum quasicrystals. We present the first results from this new kind of lattice spectroscopy, measuring the effect of phasonic and phononic driving on an ultracold quantum gas in a quasiperiodic optical potential above and below the Aubry-Andre localization transition.