Dynamical quantum phase transitions in discrete time crystals

TL;DR

This paper demonstrates that dynamical quantum phase transitions, previously observed in time-independent systems, also occur in periodically driven discrete time crystals, with potential observation in ultra-cold atomic gases.

Contribution

It extends the concept of dynamical quantum phase transitions to non-equilibrium periodically driven systems like discrete time crystals.

Findings

Dynamical quantum phase transitions occur in discrete time crystals.

Return probability shows singularities indicating phase transitions.

Potential experimental observation in ultra-cold atomic gases.

Abstract

Discrete time crystals are related to non-equilibrium dynamics of periodically driven quantum many-body systems where the discrete time translation symmetry of the Hamiltonian is spontaneously broken into another discrete symmetry. Recently, the concept of phase transitions has been extended to non-equilibrium dynamics of time-independent systems induced by a quantum quench, i.e. a sudden change of some parameter of the Hamiltonian. There, the return probability of a system to the ground state reveals singularities in time which are dubbed dynamical quantum phase transitions. We show that the quantum quench in a discrete time crystal leads to dynamical quantum phase transitions where the return probability of a periodically driven system to a Floquet eigenstate before the quench reveals singularities in time. It indicates that dynamical quantum phase transitions are not restricted to time-independent systems and can be also observed in systems that are periodically driven. We discuss how the phenomenon can be observed in ultra-cold atomic gases.