Enhancement of genuine multipartite entanglement and purity of three qubits under decoherence via bang–bang pulses with finite period

Abstract

We propose a scheme to control the dynamics of genuine multipartite entanglement and purity of qubits within spatially separated thermal baths using the bang---bang pulses with finite period. The qubits are initially entangled and have no direct interactions. The genuine multipartite entanglement of the system is measured by an entanglement monotone based on a generalization of the Peres---Horodecki criterion to multipartite systems. We first derive a master equation to describe the non-Markovian dynamics of an arbitrary number of qubits within their baths with decoherence and dynamical decoupling. Then, we calculate the entanglement monotone and purity of three qubits in super-Ohmic, sub-Ohmic, and Ohmic baths numerically. The effects of the period of pulses on the non-Markovian dynamics of qubits are discussed. We show the genuine multipartite entanglement and purity can be simultaneously improved by applying the bang---bang pulses with finite period. In particular, the bang---bang pulses with finite period are more efficient when the qubits are put into the sub-Ohmic or Ohmic baths than the case of the super-Ohmic bath.