We present a comprehensive theoretical investigation of high-order harmonic generation in ${\mathrm{H}}_{2}{}^{+}$ molecules within a quantum-optical framework. Our study focuses on characterizing various quantum-optical and quantum-information measures stemming from the correlations established between light and matter. We demonstrate the emergence of entanglement between electron and light states after the laser-matter interaction. We also identify the possibility of obtaining nonclassical states of light in targeted frequency modes by conditioning on specific electronic quantum states, which turn out to be crucial in the generation of highly nonclassical entangled states between distinct sets of harmonic modes. Our findings open up avenues for studying strong-laser-field-driven interactions in molecular systems under a fully quantum-mechanical framework.We present a comprehensive theoretical investigation of high-order harmonic generation in ${\mathrm{H}}_{2}{}^{+}$ molecules within a quantum-optical framework. Our study focuses on characterizing various quantum-optical and quantum-information measures stemming from the correlations established between light and matter. We demonstrate the emergence of entanglement between electron and light states after the laser-matter interaction. We also identify the possibility of obtaining nonclassical states of light in targeted frequency modes by conditioning on specific electronic quantum states, which turn out to be crucial in the generation of highly nonclassical entangled states between distinct sets of harmonic modes. Our findings open up avenues for studying strong-laser-field-driven interactions in molecular systems under a fully quantum-mechanical framework.

Physical Review AMar 8, 202415 citations

Non-classical States of Light After High-Harmonic Generation in Molecular and Solid Systems

Javier Rivera-Dean

Springer thesesJan 1, 20240 citations

Nonclassical effects in high-order harmonic radiation

Fu Yifei, ZHAO Di, GAO Shaoyan +1 more

High-order harmonic generation (HHG) is a significant nonlinear phenomenon triggered by the interaction of intense laser fields with matter. As a high-quality coherent light source, it has found extensive applications in areas such as attosecond pulse generation and ultrafast spectroscopy. Recent studies have revealed the prevalent existence of nonclassical effects in high-harmonic radiation, including nonclassical photon statistics, intermodal correlations, and entanglement. It holds broad development prospects in directions including the generation of nonclassical states with high photon numbers, precise control of entanglement in solid-state systems, and integration with cavity quantum electrodynamics. This review systematically summarizes the research progress concerning the nonclassical effects in HHG. It begins with an overview of the semiclassical model and strong-field quantum theory, clarifying the differences in the quantum properties of harmonic fields when driven by coherent states versus nonclassical states. Subsequently, it focuses on various physical schemes for generating nonclassical optical field states, such as optical cat states and squeezed states, via this process. Research on strong-field HHG not only deepens our understanding of the fundamental nature of intense laser physics but also opens new avenues for the generation and application of quantum light sources in the extreme ultraviolet to X-ray spectral regions.High-order harmonic generation (HHG) is a significant nonlinear phenomenon triggered by the interaction of intense laser fields with matter. As a high-quality coherent light source, it has found extensive applications in areas such as attosecond pulse generation and ultrafast spectroscopy. Recent studies have revealed the prevalent existence of nonclassical effects in high-harmonic radiation, including nonclassical photon statistics, intermodal correlations, and entanglement. It holds broad development prospects in directions including the generation of nonclassical states with high photon numbers, precise control of entanglement in solid-state systems, and integration with cavity quantum electrodynamics. This review systematically summarizes the research progress concerning the nonclassical effects in HHG. It begins with an overview of the semiclassical model and strong-field quantum theory, clarifying the differences in the quantum properties of harmonic fields when driven by coherent states versus nonclassical states. Subsequently, it focuses on various physical schemes for generating nonclassical optical field states, such as optical cat states and squeezed states, via this process. Research on strong-field HHG not only deepens our understanding of the fundamental nature of intense laser physics but also opens new avenues for the generation and application of quantum light sources in the extreme ultraviolet to X-ray spectral regions.

Zhongguo kexue. Wulixue Lixue TianwenxueMar 9, 20260 citations

Mechanisms for the Generation of Nonclassical Light

G. S. Agarwal

NATO ASI series. Series B : PhysicsJan 1, 19891 citation

Two-electron-state molecule in strong electric fields

József Somlói, András Lörincz

The paper deals with the interaction of strong and pulsed radiation fields with a two-electron-state molecule. The light pulses under discussion are shorter than a vibrational period. The molecule is treated within the framework of the Born-Oppenheimer approximation. The nuclear degree of freedom is modeled as displaced harmonic potentials for the ground and the excited electronic states, respectively. Using coherent states as expansion tools for the nuclear motion, analytical expressions are given for the short-pulse region defined by the duration of the light pulse and the displacement of the potentials. The resonance condition is derived for this region. It is shown that within the short-pulse region the two-electron-state molecule mimics the behavior of a two-electron-state atom. Longer pulses are treated with numerical methods. The concept of resonance is discussed for the longer-pulse case. Limitations on population inversion are considered.The paper deals with the interaction of strong and pulsed radiation fields with a two-electron-state molecule. The light pulses under discussion are shorter than a vibrational period. The molecule is treated within the framework of the Born-Oppenheimer approximation. The nuclear degree of freedom is modeled as displaced harmonic potentials for the ground and the excited electronic states, respectively. Using coherent states as expansion tools for the nuclear motion, analytical expressions are given for the short-pulse region defined by the duration of the light pulse and the displacement of the potentials. The resonance condition is derived for this region. It is shown that within the short-pulse region the two-electron-state molecule mimics the behavior of a two-electron-state atom. Longer pulses are treated with numerical methods. The concept of resonance is discussed for the longer-pulse case. Limitations on population inversion are considered.

Physical Review AMar 1, 19918 citations

We present a comprehensive theoretical investigation of high-order harmonic generation in

{\mathrm{H}}_{2}{}^{+}

molecules within a quantum-optical framework. Our study focuses on characterizing various quantum-optical and quantum-information measures stemming from the correlations established between light and matter. We demonstrate the emergence of entanglement between electron and light states after the laser-matter interaction. We also identify the possibility of obtaining nonclassical states of light in targeted frequency modes by conditioning on specific electronic quantum states, which turn out to be crucial in the generation of highly nonclassical entangled states between distinct sets of harmonic modes. Our findings open up avenues for studying strong-laser-field-driven interactions in molecular systems under a fully quantum-mechanical framework.