Two-Photon Excitation Sets Limit to Entangled Photon Pair Generation from Quantum Emitters

Area of Science:

• Quantum optics
• Solid-state quantum emitters

Background:

• Entangled photon pairs are crucial for quantum technologies.
• Semiconductor quantum dots are promising sources for on-demand entangled photons.
• Excitonic fine-structure splitting limits entanglement fidelity.

Purpose of the Study:

• Investigate entanglement limitations in quantum dots beyond fine-structure splitting.
• Analyze the impact of finite excitation pulse duration on entanglement.
• Identify the origin of entanglement degradation in optically excited emitters.

Main Methods:

• Theoretical analysis of a two-photon resonance scheme in a four-level quantum emitter.
• Modeling the effect of finite laser pulse duration on exciton states.
• Calculating the degree of entanglement (concurrence) under dynamic conditions.

Main Results:

• Entanglement fidelity does not reach unity even when fine-structure splitting is absent.
• Finite excitation pulse duration dynamically induces exciton state splitting.
• The excitation process itself is a limiting factor for achievable photon entanglement.

Conclusions:

• The duration of the excitation pulse fundamentally limits the maximum achievable entanglement.
• Dynamically induced splitting by the laser pulse degrades photon entanglement.
• Achieving high-fidelity entangled photons requires careful consideration of the excitation process in quantum dot emitters.