Different Types of Photon Entanglement from a Constantly Driven Quantum Emitter Inside a Cavity

Abstract

Bell states are the most prominent maximally entangled photon states. In a typical four‐level emitter, like a semiconductor quantum dot, the photon states exhibit only one type of Bell state entanglement. By adding an external driving to the emitter system, also other types of Bell state entanglement are reachable without changing the polarization basis. In this work, it is shown under which conditions the different types of entanglement occur and analytical equations are given to explain these findings. Furthermore, special points are identified, where the concurrence, being a measure for the degree of entanglement, drops to zero, while the coherences between the two‐photon states stay strong. Results of this work pave the way to achieve a controlled manipulation of the entanglement type in practical devices.

Time-dependent switching of the photon entanglement type using a driven quantum emitter–cavity system

“…Employing a FLE, ΦBS entanglement in the chosen basis of linearly polarized photons was demonstrated for various conditions in both theoretical and experimental studies . In contrast, ΨBS entanglement in the same linearly polarized basis has only been predicted in the case of continuous laser driving 38,39 . For the driven FLE laser-dressed states emerge, which have been observed experimentally 40,41 .…”

“…For the driven FLE laser-dressed states emerge, which have been observed experimentally 40,41 . By embedding the FLE inside a microcavity with cavity modes tuned in resonance with the desired emission process, certain two-photon emission processes between the laser-dressed states can be favored 38,39 . The emerging type and degree of entanglement depends strongly on the dominant two-photon emission path between the laser-dressed states, which, in turn can be tuned by the external driving strength 39 .…”

“…Furthermore, important loss processes, i.e., radiative decay with rate γ and cavity losses with rate κ, are included using Lindblad-type operators 39,46 . The time evolution of the statistical operator of the system and twotime correlation functions are calculated by numerically solving the resulting Liouville-von Neumann equation 47 .…”

“…The system parameters for the calculations are displayed in Table I 38,39 . Initially the system is in the FLE ground state |G without any cavity photons.…”

“…In standard experiments ρ 2p is reconstructed employing quantum state tomography 49 and, consequently, it is obtained from the averaged correlation functions as detailed in Ref. 39.…”