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

TL;DR

This paper investigates how two qubits coupled to XY spin baths exhibit a sudden transition in decoherence, which can be used to characterize quantum phase transitions and can be controlled using bang-bang pulses.

Contribution

It provides an explicit expression for quantum discord in this system and demonstrates control over the transition time with pulse schemes.

Findings

Sudden transition occurs near the critical point of the spin bath.

Quantum discord dynamics can be explicitly calculated.

Bang-bang pulses can prolong the transition time.

Abstract

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