Periodic driving induced helical Floquet channels with ultracold atoms in momentum space

Abstract

Employing the external degrees of freedom of atoms as synthetic dimensions renders easy and new accesses to quantum engineering and quantum simulation. As a recent development, ultracold atoms suffering from two-photon Bragg transitions can be diffracted into a series of discrete momentum states to form a momentum lattice. Here we provide a detailed analysis on such a system, and, as a concrete example, report the observation of robust helical Floquet channels, by introducing periodic driving sequences. The robustness of these channels against perturbations is confirmed, as a test for their topological origin captured by Floquet winding numbers. The periodic switching demonstrated here serves as a testbed for more complicated Floquet engieering schemes, and offers exciting opportunities to study novel topological physics in a many-body setting with tunable interactions.

Floquet engineering topological Dirac bands

“…We show that, taken over the whole BZ, these trajectories cover the Bloch sphere, giving winding numbers of ±1 for initial pseudospins |↑↓ . A related experiment in a small synthetic dimension chain observed the drift of initially localized states [12] but not the linear drift of crystal momentum eigenstates nor the band topology.…”

Synthetic topology and Floquet dynamic quantum phase transition in a periodically driven Raman lattice

“…Alternatively, dynamic topological phenomena also emerge in periodically driven Floquet systems [21][22][23][24][25][26][27][28][29][42][43][44][45][46][47][48]. In the simplest Floquet configuration, a Floquet operator U is repeatedly acted on the instantaneous state of the system, such that the overall time evolution is seen as a stroboscopic simulation of the continuous-time evolution driven by an effective Hamiltonian H eff , with U = e −iH eff T [51][52][53].…”

“…Since H eff can possess band topology, the Floquet dynamics can be regarded as a discrete-time quench process of a topological Hamiltonian. Along this vein of thought, dynamic skyrmions and DQPTs have recently been observed in discrete-time quantum walks of single-photons and cold atoms [28,48,49]. Here DQPT is the temporal analogue of continuous phase transitions, characterized by non-analyticities in the time evolution of physical observables.…”