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

Abstract

The cascaded decay in a four-level quantum emitter is a well-established mechanism to generate polarization-entangled photon pairs, the building blocks of many applications in quantum technologies. The four most prominent maximally entangled photon pair states are the Bell states. In a typical experiment based on an undriven emitter, only one type of Bell state entanglement can be observed in a given polarization basis. Other types of Bell state entanglement in the same basis can be created by continuously driving the system by an external laser. In this work, we propose a protocol for time-dependent entanglement switching in a four-level quantum emitter–cavity system that can be operated by changing the external driving strength. By selecting different two-photon resonances between the laser-dressed states, we can actively switch back and forth between the different types of Bell state entanglement in the same basis as well as between entangled and nonentangled photon pairs. This remarkable feature demonstrates the possibility to achieve a controlled, time-dependent manipulation of the entanglement type that could be used in many innovative applications.

Quantum Communication Using Semiconductor Quantum Dots

“…While the two‐photon state emitted by the XX‐X radiative cascade is typically limited to the $${\vert\Psi ^{\pm }\rangle}$$ Bell states, schemes for the generation of arbitrary entangled states were recently proposed. [ 141,142 ] Importantly, several in‐situ or post‐growth techniques can be used to tune the FSS to zero, with piezo‐induced strain tuning being one of the most powerful approaches to date. [ 143 ] The possibility to generate polarization entanglement—being one crucial ingredient for many schemes of quantum communication—is a major advantage of using engineered QD devices.…”

Phonon-induced transition between entangled and nonentangled photon emission in constantly driven quantum-dot--cavity systems

“…Indeed, various theoretical and experimental studies demonstrated the possibility to obtain ΦBS entanglement in the chosen basis of linearly polarized photons [11,18,19,. Furthermore, recent theoretical studies [10,21,46] showed that a four-level emitter-cavity system, e.g., a QD embedded inside a cavity, can also facilitate the creation of ΨBS entanglement, when a constant laser driving is applied to the emitter. In this setup, four laserdressed states emerge and their characteristics depend on the applied driving strength.…”

“…By adjusting the cavity modes to a direct two-photon transition between these dressed states, entangled photon pairs can be created. The resulting type and degree of entanglement depends crucially on the applied driving strength and the energy of the cavity modes [10,46].…”