In a groundbreaking study conducted by scientists from the National University of Singapore (NUS), it was demonstrated that excitonic resonances and interactions between excitons play a crucial role in increasing the efficiency of generating entangled photon pairs. This discovery holds immense significance as it could potentially lead to the development of highly efficient ultrathin quantum light sources, revolutionizing the field of quantum technologies.
Quantum entanglement serves as the foundation for numerous quantum technologies, showcasing a phenomenon where the properties of two quantum particles are interconnected, regardless of the distance between them. Entangled photons, being massless particles of light, are commonly produced through spontaneous parametric down-conversion (SPDC) by shining a “pump” beam on specific non-linear optical crystals. However, the efficiency of SPDC has always been a challenge, until now.
The research team, under the leadership of Associate Professor Su Ying Quek from the Department of Physics at NUS, revealed that many-body excitonic interactions within non-linear optical crystals can significantly enhance the efficiency of SPDC. Excitons, which are pairs of negative and positive charges arising from the crystal’s fundamental excitations, play a vital role in this process. The proximity of these charges influences SPDC efficiency based on the energy or frequency of the light.
The research findings, published in the journal Physical Review Letters, were based on in-depth quantum mechanical calculations analyzing the non-linear optical response of crystals to incident light while taking excitonic effects into account. Dr. Fengyuan Xuan, the lead author of the study, emphasized the importance of excitonic interactions in enhancing SPDC efficiency, showcasing the difference from conventional treatments.
The use of ultrathin crystals, contrary to the previous beliefs regarding decreased efficiency with material volume, offers a solution to the phase matching problem associated with SPDC. The stronger excitonic interactions in these ultrathin crystals alleviate efficiency concerns, making them a viable option for producing entangled photons.
The research team applied their theoretical approach to NbOI2, a layered non-linear optical material, to study both SPDC and second harmonic generation (SHG). The simulations of SHG intensities based on the polarization angle of incident light aligned well with experimental work, highlighting the efficacy of excitonic enhancements. Moreover, the frequency matching of the “pump” beam and crystal’s excitation frequencies further enhances SPDC efficiency.
The study’s findings pave the way for generating entangled photons using ultrathin materials, facilitating their seamless integration into hybrid quantum-photonic platforms for the development of next-generation quantum devices. The potential impact of excitonic interactions on enhancing quantum light sources opens up new possibilities in the realm of quantum technologies.
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