New quantum “stopwatch” can improve imaging technologies

Researchers at the University of Colorado at Boulder have designed one of the most accurate stopwatches to date, not for timing Olympic sprinters and swimmers, but for counting single photons, or the tiny bundles of energy that make up the light.

The team’s invention could lead to great improvements in a range of imaging technologies, from sensors that map entire forests and mountain ranges to more detailed devices capable of diagnosing human illnesses such as Hickory’s Disease. Alzheimer’s and cancer. The group published its results this week in the journal OPTICAL.

Bowen Li, lead author of the new study, said the research is focused on a widely applied technology called time correlated single photon counting (TCSPC). It works much like the timers you see at the Olympics: Scientists first shine a laser light on a sample of their choice, from individual proteins to massive geological formation, and then record the photons returning to them. The more photons researchers collect, the more they can learn about this object.

“TCSPC gives you the total number of photons. It also shows when each photon hits your detector,” said Li, a postdoctoral researcher in the Department of Electrical, Computer, and Power Engineering (ECEE) at CU Boulder. “It works like a stopwatch.

Now this stopwatch has become better than ever. Using a high-speed optical tool called a “temporal lens,” Li and his colleagues show that they can measure the arrival of photons with more than 100 times the accuracy of existing tools.

Shu-Wei Huang, corresponding author of the new study, added that the group’s quantum time lens works even with the cheapest TCSPC devices available on the market.

“We can add this modification to almost any TCSPC system to improve its single-photon temporal resolution,” said Huang, assistant professor at ECEE.

The research is part of the new $ 25 million Center for Quantum Systems through Tangled Science and Engineering (Q-SEnSE) led by CU Boulder.

Photo finish

TCSPC may not be a household name, Huang said. But the technology, which was first developed in 1960, has revolutionized the way humans see the world. These photon counters are important components of lidar (or light sensing and ranging) sensors, which researchers use to create geological maps. They also appear in a smaller-scale imaging approach called fluorescence lifetime microscopy. Doctors use this technique to diagnose certain diseases such as macular degeneration, Alzheimer’s disease, and cancer.

“People project a pulse of light on their sample, then measure the time it takes to emit a photon,” Li said. “This moment tells you the property of the material, like the metabolism of a cell.”

Traditional TCSPC tools, however, can only measure this time up to a certain level of accuracy: if two photons hit your device too close to each other, say at 100 trillion seconds or less, the detector records them as a single photon. It’s like two sprinters coming to a photo finish in a 100-meter sprint.

Such tiny inconsistencies can seem like a baffle, but Li noted that they can make a big difference when trying to get a detailed look at insanely small molecules.

Time lenses

So he and his colleagues decided to try to solve the problem using what scientists call a “time lens”.

“In a microscope, we use optical lenses to magnify a small object into a large image,” Li said. “Our time objective works the same way but for time.”

To understand how this time distortion works, imagine two photons like two runners neck and neck, so close the timekeeper of the Olympics cannot tell them apart. Li and his colleagues pass these two photons through their temporal lens, made up of loops of silica fibers. In the process, one of the photons slows down, while the other speeds up. Instead of a tight race, there is now a large gap between runners, which a detector can register.

“The separation between the two photons will be amplified,” Li said.

And, the team found, the strategy works: TCSPC devices with integrated temporal lenses can distinguish photons arriving at a detector with a deviation of several hundred quadrillion of a second, orders of magnitude greater than normal devices. can reach.

Researchers still have work to do before lenses become commonplace in science labs. But they hope their tool will one day allow humans to see objects, from the very small to the very large, all with a clarity that was previously impossible.