Abstract: Periodic driving has become one highly controllable and versatile tool in quantum control. Many efforts have be devoted to explore novel quantum phase transition induced by periodic driving on quantum many-body systems. Different from static systems, quantum phase transition for periodically driven systems cannot characterized by their eigen-energy, because the energy of periodically driven systems is not conserved. Thanks to Floquet theory, the properties of periodically driven systems can be well described by the Floquet eigen-states and eigen-values, which, respectively, act as quasi-stationary states and quasi-energies for such time-dependent systems.

In this talk, I will report that interesting non-equilibrium quantum phase transition can be triggered by engineering non-trivial band-gap structure and midgap bound state in Floquet quasi-energy spectrum using periodic driving. I will clarify this idea by two examples. One is to induce more colorful topological quantum phase transition in one-dimensional Kitaev model by periodic driving. A tunable number of Majorana edge modes can be generated by the well-designed periodic driving. The tenability of the number of the Majorana modes may supply a novel way to identify the formation of the Majorana modes. Another is to induce non-equilibrium quantum phase transition in the system consisting of a two-level system interacting with a coupled cavity array by periodic driving. It is found that whenever the quantum phase transition manifested by the formation of a midgap state in the Floquet quasi-energy spectrum occurs, the decoherence of the two-level system induced by the cavity array can be suppressed. This opens a door to control decoherence by periodic driving.

About the Speaker: Prof. An Jun-Hong received his Ph. D. in Physics from Lanzhou University in 2005 and then joined Lanzhou University. From 2006 to 2007, he performed postdoctoral research in National Cheng-Kung University. From 2007 to 2008 and 2009 to 2010, he worked in National University of Singapore as a research fellow. From 2010 to today, he was appointed as a visiting research fellow in National University of Singapore. Prof. An's recent research work involves decoherence of open quantum system and its control, topological phase transition, and cavity optomechanics.