Correlations in optically-controlled quantum emitters

TL;DR

This paper investigates how external laser excitation influences quantum and classical correlations in individual quantum emitters, revealing conditions where quantum correlations surpass classical ones and emphasizing the importance of proper entanglement measures.

Contribution

It analytically demonstrates that quantum discord can exceed classical correlations in quantum emitters, challenging previous assumptions, and explores how laser control can optimize quantum correlations.

Findings

Quantum discord can be greater than classical correlations during evolution.

External laser fields can enhance quantum correlations.

Proper entanglement measures are crucial for accurate analysis.

Abstract

We address the problem of optically controlling and quantifying the dissipative dynamics of quantum and classical correlations in a set-up of individual quantum emitters under external laser excitation. We show that both types of correlations, the former measured by the quantum discord, are present in the system's evolution even though the emitters may exhibit an early stage disentanglement. In the absence of external laser pumping,we demonstrate analytically, for a set of suitable initial states, that there is an entropy bound for which quantum discord and entanglement of the emitters are always greater than classical correlations, thus disproving an early conjecture that classical correlations are greater than quantum correlations. Furthermore, we show that quantum correlations can also be greater than classical correlations when the system is driven by a laser field. For scenarios where the emitters' quantum correlations are below their classical counterparts, an optimization of the evolution of the quantum correlations can be carried out by appropriately tailoring the amplitude of the laser field and the emitters' dipole-dipole interaction. We stress the importance of using the entanglement of formation, rather than the concurrence, as the entanglement measure, since the latter can grow beyond the total correlations and thus give incorrect results on the actual system's degree of entanglement.