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arXiv · 2405.15022

Evidence of the quantum-optical nature of high-harmonic generation

David Theidel·Viviane Cotte·René Sondenheimer·Viktoriia Shiriaeva·Marie Froidevaux·Vladislav Severin·Philip Mosel·Adam Merdji-Larue·Sven Fröhlich·Kim-Alessandro Weber·Uwe Morgner·Milutin Kovacev·Jens Biegert·Hamed Merdji
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Abstract

High-harmonic generation is a light up-conversion process occurring in a strong laser field, leading to coherent bursts of extreme ultrashort broadband radiation [1]. As a new perspective, we propose that ultrafast strong-field electronic or photonic processes such as high-harmonic generation can potentially generate non-classical states of light well before the decoherence of the system occurs [2, 3]. This could address fundamental challenges in quantum technology such as scalability, decoherence or the generation of massively entangled states [4]. Here, we report experimental evidence of the non-classical nature of the harmonic emission in several semiconductors excited by a femtosecond infrared laser. By investigating single- and double beam intensity cross-correlation [5], we measure characteristic, non-classical features in the single photon statistics. We observe two-mode squeezing in the generated harmonic radiation, which depends on the laser intensity that governs the transition from Super-Poissonian to Poissonian photon statistics. The measured violation of the Cauchy-Schwarz inequality realizes a direct test of multipartite entanglement in high-harmonic generation [6]. This result is supported by the theory of multimodal detection and the Hamiltonian from which the effective squeezing modes of the harmonics can be derived [7, 8]. With this work, we show experimentally that high-harmonic generation is a new quantum bosonic platform that intrinsically produces non-classical states of light with unique features such as multipartite broadband entanglement or multimode squeezing. The source operates at room temperature using standard semiconductors and a standard commercial fiber laser, opening new routes for the quantum industry, such as optical quantum computing, communication and imaging.

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David Theidel, Viviane Cotte, René Sondenheimer, Viktoriia Shiriaeva, Marie Froidevaux, Vladislav Severin, Philip Mosel, Adam Merdji-Larue, Sven Fröhlich, Kim-Alessandro Weber, Uwe Morgner, Milutin Kovacev, Jens Biegert, Hamed Merdji. 2024-05-23. Evidence of the quantum-optical nature of high-harmonic generation. https://doi.org/10.1103/prxquantum.5.040319

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