A new path toward high-energy quantum light

The laws of classical physics can describe the world we observe around us. But, when we see at the atomic scale, the strange world of quantum physics takes over.

Light is no different; from radio waves to sunlight, it can mainly be explained using classical physics. The so-called quantum fluctuations, however, start to operate at the micro- and nanoscale, and classical physics is unable to describe them.

Scientists from the University of Cambridge and colleagues from the US, Israel, and Austria overcame this constraint by building a quantum-optical theory of strongly driven many-body systems. Through this, they showed the presence of correlations among the emitters creates the emission of non-classical many-photon states of light.

In other words, they have developed a theory to describe a new state of light, which has controllable quantum properties over a broad range of frequencies, up as high as X-ray frequencies. Their theory states a new mechanism for generating high-energy’ quantum light’. This quantum light could help determine new properties of matter at the atomic scale.

Dr. Andrea Pizzi, who researched while based at Cambridge’s Cavendish Laboratory, said, “Quantum fluctuations make quantum light harder to study, but also more interesting: if correctly engineered, quantum fluctuations can be a resource. Controlling quantum light’s state could enable new microscopy and quantum computation techniques.”

Typically, intense lasers are used to generate light. When a powerful enough laser is directed onto a group of emitters, it can pull some of the emitters’ electrons away, energizing them. Some of these electrons eventually reunite with the emitters from which they were originally removed, and the extra energy they absorb is transformed into light. The low-frequency input light is converted into high-frequency output radiation through this mechanism.

It has been assumed that each emitter operates independently of the others, producing output light with minimal quantum fluctuations. The state of one particle provides information about the state of another; hence scientists were interested in studying a system where the emitters are not independent but rather correlated. The output light in this scenario begins to behave considerably differently, and its quantum fluctuations take on a highly organized appearance that makes them potentially more valuable.

To solve this many-body problem, scientists used a combination of theoretical analysis and computer simulations. There, the output light from a group of correlated emitters could be described using quantum physics.

The theory shows that correlated emitters with a powerful laser can produce regulated quantum light. The technique has high-energy output light and might be used to modify the X-rays’ quantum-optical structure.

Pizzi said, “We worked for months to get the equations cleaner and cleaner until we got to the point where we could describe the connection between the output light and the input correlations with just one compact equation. As a physicist, I find this beautiful. Looking forward, we would like to collaborate with experimentalists to provide validation of our predictions. On the theory side of things, our work suggests many-body systems as a resource for generating quantum light, a concept we want to investigate more broadly beyond the setup considered in this work.”

Journal Reference:

1. Andrea Pizzi et al.’ Light emission from strongly driven many-body systems.’ Nature Physics (2023). DOI: 10.1038/s41567-022-01910-7