Scientists Make Quantum Light Breakthrough: 'This Experiment Is Beautiful'

In a mind-warping milestone experiment, scientists have been able to manipulate small numbers of individual photons of light, opening doors for the development of quantum technologies.

This research, published in the journal Nature Physics on March 20, describes how the researchers were able to make two photons of light interact and measure the difference between these interacting photons and a single photon.

"This experiment is beautiful, not only because it validates a fundamental effect – stimulated emission – at its ultimate limit, but it also represents a huge technological step towards advanced applications," co-lead author Natasha Tomm from the University of Basel, said in a statement.

Quantum physics is the study of subatomic particles, like photons, quarks and neutrinos. Photons are massless quantum particles that make up visible light and all other electromagnetic wavelengths, and they have wave–particle duality, meaning that their behavior features properties of both waves and particles.

"This opens the door to the manipulation of what we can call 'quantum light'," co-lead author Sahand Mahmoodian from the University of Sydney School of Physics, said in a statement. "This fundamental science opens the pathway for advances in quantum-enhanced measurement techniques and photonic quantum computing."

In their experiments, the scientists shot both a single photon and a pair of bound photons at an artificial atom called a quantum dot, and found that they could measure a direct time delay between the photon on its own and the ones that were bound.

"The device we built induced such strong interactions between photons that we were able to observe the difference between one photon interacting with it compared to two," Tomm said.

"We observed that one photon was delayed by a longer time compared to two photons. With this really strong photon-photon interaction, the two photons become entangled in the form of what is called a two-photon bound state."

Photons usually don't interact with each other, which makes light so good for its use in communication via optical fibers, as there is little information distortion. However, by making these small numbers of photons interact, scientists can use the measured difference between interacting photons and single photons to get high quality readings in cases where using large amounts of light would damage the sample or not give enough resolution, for example in biological microscopy.

The process that the scientists used to manipulate the small number of photons, stimulated light emission, is the same process that powers lasers, which uses many more photons. These manipulations of photons have allowed for a range of amazing technologies, including GPS, computers, medical imaging and global communications networks.

The researchers plan to carry out further experiments and eventually use these techniques to make better quantum computers.

"We can apply the same principles to develop more-efficient devices that give us photon bound states. This is very promising for applications in a wide range of areas: from biology to advanced manufacturing and quantum information processing," said Tomm.

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