‘Quantum light’ breakthrough could revolutionize science at the atomic level

CAMBRDIGE, United Kingdom — “Quantum light” may sound like something out of a Marvel movie, but scientists say it may hold the real-world key to revolutionizing science as we know it. An international team says generating this high-energy light and controlling it can unlock a whole new realm in quantum computing.

Researchers from the University of Cambridge, as well as scientists in the United States, Israel, and Austria, have come up with a theory describing this new state of light. They say it has controllable quantum properties and a wide range of frequencies which reach X-ray levels. Harnessing this power could lead to advances in microscopy — or the ability to see incredibly small things normally invisible to the naked eye.

Life looks completely different at the atomic level

Scientists say the world we see every day with our eyes follows the laws of classical physics. However, when you look at things on the atomic level, study authors say you’re able to see the “strange world of quantum physics.” While a rubber ball is just a ball that bounces under the laws of classical physics, the atoms that make up this ball follow a completely different set of rules.

“Light is no exception: from sunlight to radio waves, it can mostly be described using classical physics,” says lead author Dr. Andrea Pizzi, who carried out the research at Cambridge’s Cavendish Laboratory, in a university release. “But at the micro and nanoscale so-called quantum fluctuations start playing a role and classical physics cannot account for them.”

Pizzi and the team are now working on a theory that can predict a new way of controlling the quantum nature of light.

“Quantum fluctuations make quantum light harder to study, but also more interesting: if correctly engineered, quantum fluctuations can be a resource,” Pizzi says. “Controlling the state of quantum light could enable new techniques in microscopy and quantum computation.”

Scientists are trying to harness energy from laser light

One of the main ways scientists generate light is by using powerful lasers. When researchers point a strong laser beam at a collection of emitters, it literally rips electrons away from the emitters and energizes them. Eventually, these charged up particles merge with the emitter again, with the excess energy shining as visible light. This whole process turns low-frequency input light into high-frequency output radiation.

“The assumption has been that all these emitters are independent from one another, resulting in output light in which quantum fluctuations are pretty featureless,” Pizzi explains. “We wanted to study a system where the emitters are not independent, but correlated: the state of one particle tells you something about the state of another. In this case, the output light starts behaving very differently, and its quantum fluctuations become highly structured, and potentially more useful.”

Scientists refer to this issue as a “many body problem.” Using computer simulations, the team tried to solve the problem by describing the output light using quantum physics. Researchers say their model demonstrates that they can generate controllable quantum light on correlated emitters using a strong laser.

“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,” Pizzi concludes. “Looking forward, we would like to collaborate with experimentalists to provide a 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 that we want to investigate more broadly, beyond the setup considered in this work.”

What does all this have to do with quantum computers?

Controlling light and electrons is at the heart of quantum computing. While traditional computers use, binary digits or “bits” (0s and 1s) to process information, a quantum bit (qubit) exists in both states at the same time.

Qubits use quantum objects which act as information processors — such as spin (controlling the spin of charged particles in a semiconductor), trapped atoms or ions, photons (particles of light), or semiconducting circuits. Controlling the spin of these electrons is the key to making qubits work in an ultra-fast computer.

In a nutshell, quantum computers find better and quicker ways to solve problems. Scientists believe quantum technology could solve extremely complex problems in seconds, while traditional supercomputers you see today need months or even years to crack certain codes.

The study is published in the journal Nature Physics.

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