Non-perturbative interactions, which refer to interactions that are too strong to be described by perturbation theory, have long intrigued researchers in the field of light and matter. However, the quantum properties of light and their influence on these interactions have largely remained unexplored. In a recent study published in Nature Physics, researchers at the Technion–Israel Institute of Technology introduced a new theory that delves into the physics behind non-perturbative interactions driven by quantum light. This groundbreaking theory not only sheds light on fundamental phenomena but also paves the way for future experiments and the development of quantum technology.
The study was a result of a collaboration between three research groups at Technion, led by Prof. Ido Kaminer, Prof. Oren Cohen, and Prof. Michael Krueger. The paper’s co-first authors, Alexey Gorlach and Matan Even Tsur, spearheaded the study, with support and ideas from Michael Birk and Nick Rivera. The researchers embarked on a scientific journey in 2019, driven by their interest in high harmonic generation (HHG) and its quantum aspects. At that time, classical explanations dominated HHG experiments, and the team was eager to explore when and how quantum physics plays a role in this context.
The researchers were intrigued by the fact that several foundational phenomena in physics were explained by different theories, making it impossible to establish connections between them. For example, HHG relied on a theory that contradicted the theory applied to spontaneous emission. This incongruity prompted the team to seek a unifying framework that could account for all photonics phenomena, including HHG. In their 2020 paper published in Nature Communications, Prof. Kaminer and his research group proposed a version of this framework, analyzing HHG using the language of quantum optics. This study was a vital stepping stone towards understanding quantum HHG.
Despite the progress made in quantum HHG, all HHG experiments were still conducted using classical laser fields. The idea that quantum light could be intense enough to generate HHG seemed implausible until Prof. Maria Chekhova demonstrated the creation of intense quantum light in the form of bright squeezed vacuum. This groundbreaking work served as the motivation for the researchers’ new investigation.
In their recent study, Prof. Kaminer, Gorlach, and their colleagues devised a comprehensive framework that describes strong-field physics processes driven by quantum light. To validate their framework, they applied it to HHG and predicted the changes that would occur when driven by quantum light. Surprisingly, the researchers found that important features, such as intensity and spectrum, were significantly affected by the quantum photon statistics of the driving light source. Their paper also predicts experimentally feasible scenarios that can only be explained by considering the photon statistics. These upcoming experiments are expected to have a significant impact on the field of strong-field quantum optics.
It is important to note that the work carried out by the researchers at Technion so far is purely theoretical. Their paper presents the first theory of non-perturbative processes driven by quantum light and demonstrates that the quantum state of light influences measurable quantities, such as the emitted spectrum. The researchers developed a unique computational scheme based on the split representation of the driving light into the generalized Glauber distribution or the Husimi distribution. By combining these simulations with the time-dependent Schrodinger equation (TDSE), they derived an overall result applicable to any quantum state of light and system of emitters.
Expanding the Scope of Application
The theory proposed by Prof. Kaminer, Gorlach, and their colleagues holds great potential for further studies in various physics domains. Beyond HHG, the theory can be applied to a wide range of non-perturbative processes driven by non-classical light sources. For example, it can be directly applied to the generation of attosecond pulses via HHG, which plays a vital role in quantum sensing and imaging technologies. Another potential application lies in the Compton effect, a process used to generate X-ray pulses. The team has already published a follow-up paper on this topic in Science Advances and is actively working towards performing the experiment discussed in the paper.
As the researchers continue to advance their theory, their overarching goal is to expand its applicability beyond HHG and delve into the quantum effects of intense light in various materials. This convergence of quantum optics and condensed matter physics holds great promise for future developments in quantum technology. The study conducted by Prof. Kaminer, Gorlach, and their colleagues represents a significant breakthrough in understanding the role of quantum light in non-perturbative interactions. Their theoretical framework provides a foundation for further exploration and experimentation, opening up new possibilities for the field of strong-field quantum optics.
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