Quantum correlations and violation of Bell inequality induced by External Field in a two photon radiative cascade

TL;DR

This paper demonstrates that an external field can revive quantum correlations and enable Bell inequality violation in a two-photon cascade, despite energy splitting and dephasing effects.

Contribution

It introduces a method to control and preserve quantum correlations in photon pairs using an external field, overcoming typical degradation factors.

Findings

External field induces Stark shift and dressed states, reviving correlations.

Quantum correlations can be maintained despite energy splitting and dephasing.

External control enables Bell inequality violation under conditions previously prohibitive.

Abstract

We study the polarization dependent second order correlation of a pair of photons emitted in a four level radiative cascade driven by an external field. It is found that the quantum correlations of the emitted photons, degraded by the energy splitting of the intermediate levels in the radiative cascade can be efficiently revived by a far detuned external field. The physics of this revival is linked to an induced stark shift and the formation of dressed states in the system by the non-resonant external field. Further, we investigated the competition between the effect of the coherent external field and incoherent dephasing of the intermediate levels. We found that the degradation of quantum correlations due to the incoherent dephasing can be content for small dephasing with the external field. We also studied the non-locality of the correlations by evaluating the Bell's inequality in the linear polarization basis for the radiative cascade. We find that the Bell parameter decreases rapidly with increase in the intermediate level energy splitting or incoherent dephasing rate to the extent that there is no violation. However, the presence of an external field leads to control over the degrading mechanisms and preservation of nonlocal correlation among the photons. This in turn can induce, violation of Bell's inequality in the radiative cascade for arbitrary intermediate level splitting and small incoherent dephasing.