Harnessing the power of quantum entanglement has long been a goal of scientists working in the field of quantum technologies. The ability to generate entangled photon pairs efficiently is crucial for the development of quantum light sources. Scientists from the National University of Singapore (NUS) have recently made significant progress in this area by demonstrating that excitonic resonances and interactions between excitons can enhance the efficiency of generating entangled photon pairs.
Excitonic interactions play a crucial role in increasing the efficiency of spontaneous parametric down-conversion (SPDC) – the process through which entangled photons are typically generated. These interactions occur between negative and positive charges created when light interacts with a non-linear optical crystal. Known as excitons, these pairs of opposite charges are fundamental excitations of the crystal.
The research team led by Associate Professor Su Ying Quek from the Department of Physics at NUS found that bringing these opposite charges closer together can significantly enhance the efficiency of SPDC. By analyzing the non-linear optical response of crystals using quantum mechanical calculations, the team was able to demonstrate that the probability of transitions between fundamental excitations increases when the opposite charges are in close proximity.
One of the technical challenges associated with SPDC is the phase matching problem, which is effectively addressed by using ultrathin crystals. While conventional wisdom suggested that the efficiency of SPDC decreases with the material volume in ultrathin crystals, the team at NUS discovered that stronger excitonic interactions in these crystals can actually alleviate this effect. This makes ultrathin crystals a promising source for producing entangled photons.
The team at NUS applied their theoretical approach to NbOI2, a layered non-linear optical material, and found that the excitonic enhancement is particularly strong when the frequency of the “pump” beam closely matches an excitation frequency in the crystal. This discovery opens up possibilities for generating entangled photons using ultrathin materials, which can be easily integrated into hybrid quantum-photonic platforms for next-generation devices.
The research conducted by the team at NUS holds significant promise for improving the efficiency of generating entangled photon pairs. By leveraging excitonic resonances and interactions in non-linear optical crystals, the team has demonstrated a novel approach to enhancing SPDC efficiency. This work not only contributes to the advancement of quantum technologies but also opens up new possibilities for the development of ultrathin quantum light sources.
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