A strong physics theory of the unperturbed field driven by quantum light

Non-interference interactions (that is, interactions too strong to be explained by the so-called interference theory) between light and matter have been the subject of many research studies. However, the role that the quantum properties of light play in these interactions and the phenomena that arise from them have so far not been widely explored.

Researchers at the Technion-Israel Institute of Technology have recently introduced a new theory that explains the physics that underpins the interference-free communication driven by quantum light. Their theory, introduced into it Natural Physicsit can guide future experiments that explore strong physical phenomena, and the development of new quantum technologies.

This latest paper is the result of a close collaboration between three different research groups at the Technion, led by principal researchers Prof. Ido Kaminer, Prof. Oren Cohen and Prof. Michael Krueger. Students Alexey Gorlach and Matan Even Tsur, first authors of the paper, continued the study, with support and ideas from Michael Birk and Nick Rivera.

“This was a great scientific journey for us,” Prof. Kaminer and Gorlach told Phys.org. “We started to think about high harmonic generation (HHG) and its quantum properties already in 2019. After that, the light in all HHG experiments was described classically and we wanted to find out when quantum physics started to play a role there.

“In fact, it bothered us that many of the fundamentals of physics were each explained by a completely different theory, thus it was impossible to relate them. For example, HHG was based on an idea that contradicted the idea usually used to calculate spontaneous emission—each explained on a different basis.”

HHG is a highly nonlinear physical process involving strong interactions between light and matter. In particular, it occurs when intense pulses of light injected into matter cause it to emit the so-called high-harmonics of the pulse of intense light.

In a few years, Prof. Kaminer and his research team attempted to develop a quantum theory-based framework that would encompass all photonics phenomena, including HHG. Their first paper on this topic, published in Nature Communication in 2020, introduced a proposed version of this synthesis framework, analyzing HHG in the language of quantum optics.

“This study has contributed to opening up the now growing field of quantum HHG,” Prof. Kaminer and Gorlach explain. “Still, all HHG experiments were conducted with primitive laser fields. It seemed that there was no quantum light strong enough to create HHG. However, the works of Prof. Maria Chekhova showed that it is possible to create enough light in the quantum form known as light squeezed vacuum. This inspired our new research.”

As part of their new study, Prof. Kaminer, Gorlach and their colleagues developed a comprehensive framework that describes the strong physical processes driven by quantum light. To theoretically validate their framework, they applied it to HHG, predicting how this process would change if it were driven by quantum light.

“We have shown that contrary to expectations, many important factors such as intensity and spectrum, all change due to the use of a light source for conduction with different numbers of quantum photons,” said Prof. Kaminer and Gorlach. “The paper we wrote also predicts possible experimental conditions that cannot be explained in any other way than considering photon statistics. This upcoming experiment will have even greater impact and importance in the growing field of sight-field quantum optics.”

So far, the work done by this group of researchers is only conceptual. Their paper introduces the first theory of non-perturbative processes driven by quantum light, while also showing theoretically that the quantum state of light affects measurable quantities, such as the emission spectrum.

“The way our theory works is to split the driving light into one of two distributions called the generalized Glauber distribution or the Husimi distribution, then using a standard equation for the HHG field, the time-dependent Schrodinger equation (TDSE), to measure the different distribution points, before combining the measurements together to get the full effect, “Prof. Kaminer and Gorlach said.

“This connection of common human tools to the scheme of quantum-optical calculation is what makes our work powerful and useful – it works in the state of light and the invisible emission system.”

A new theory taken by Prof. Kaminer, Gorlach and their colleagues can quickly bring lessons to various fields of physics. In fact, their paper aims to take the idea beyond HHG, to many invisible processes, which can all be driven by non-classical light sources.

These theoretical predictions can be quickly tested and verified in experimental settings. For example, group theory can be directly applied to the generation of attosecond pulses by HHG, a process that can support the performance of quantum sensing and quantum imaging technologies.

In this regard, the team published a recent theoretical paper Nature Photos proposed to control attosecond pulse profiles using the quantum nature of light, for example showing promising conditions using a mixture of classical light and quantum light.

In addition, their theory can be applied to other phenomena based on solid physics, such as the Compton effect, a process used to generate X-ray pulses.

“We recently published the following article on this application Advances in Sciencethat ended up appearing earlier due to delays in the peer review process,” Kaminer and Gorlach added about the Compton result. “We are now working to conduct a test that discusses the theory in our paper.

“Another ambitious goal will be to develop a theory beyond HHG, and to investigate quantum effects in various objects driven by superluminosity, linking our new developments in quantum optics to the frontiers of matter physics.”