Pulse control of sudden transition for two qubits in XY spin baths and quantum phase transition

摘要

We study the dynamics of two initially correlated qubits coupled to their ownseparate spin baths modeled by a XY spin chain and find the explicit expressionof the quantum discord for the system. A sudden transition is found to existbetween classical and quantum decoherence by choosing certain initial states.We show that the sudden transition happens near the critical point, whichprovides a new way to characterize the quantum phase transition. Furthermore,we propose a scheme to prolong the transition time of the quantum discord byapplying the bang-bang pulses.