The laws of classical physics can describe the world we observe around us. But when we look 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. However, the so-called quantum fluctuations begin to act on the micro and nano scale and classical physics cannot describe them.

Scientists from the University of Cambridge and colleagues from the US, Israel and Austria have overcome this limitation by building a quantum optic theory of highly driven many-particle systems. By doing so, they showed that the presence of correlations between the emitters causes 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 wide range of frequencies, up to X-ray frequencies. Their theory proposes 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 did research at the Cavendish Laboratory in Cambridge, said: “Quantum fluctuations make quantum light more difficult to study, but also more interesting. If designed correctly, quantum fluctuations can be a resource. Controlling the state of quantum light could enable new microscopy and quantum computation techniques.”

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

Each emitter is assumed to operate 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 in which the emitters are not independent but rather correlated. The output light in this scenario begins to behave significantly differently and the quantum fluctuations take on a highly organized appearance making 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 can be used to modify the quantum optical structure of X-rays.

pizza said, “We worked for months to get the equations cleaner and cleaner until we reached the point where we could describe the relationship between the output light and the input correlations with just one compact equation. As a physicist, I think this is wonderful. In the future, we would like to collaborate with experimenters to validate our predictions. In terms of theory, our work suggests many-particle systems as a tool for quantum light generation, a concept we intend to explore more broadly than the setup considered in this work.

Magazine reference:

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