University of Oslo Physicists Model New Photons Created by Cutting a Photon

Photons are elementary particles of light, and under normal conditions, they cannot be divided. But researchers looking closely at the dual nature of light as both a particle and an extended wave recently asked a simple question that had apparently never been posed before: What happens if you try to break a photon in half?

The analysis was conducted by theoretical physicist Johannes Skaar and his colleagues at the University of Oslo in Norway. Because photons possess spatial distribution as wave packets, the team modeled a theoretical scenario using an optical shutter—fast-moving mirrors designed to block or release light pulses—to effectively separate sections of a photon wave.

In the mathematical model, a single photon travels toward a mirror. The front half of the light wave strikes the mirror first and bounces back. Suddenly, the mirror is removed, freeing the back half of the wave to pass through. Using quantum field theory, the researchers calculated how this sudden truncation affects the waveform dynamics.

“Despite being a simple question, it appears that it has not been asked before.”

Physicists from the University of Oslo, via Gizmodo

Infinite Photons Erupting From the Quantum Vacuum

The mathematical results challenged initial expectations. Rather than producing two smaller pieces or leaving behind a vacuum and a single photon, the sudden removal of the barrier spawned a massive eruption of light particles.

According to the researchers, removing the mirror infinitely fast would conjure an infinity of light particles out of thin air. Pulling the mirror away more slowly still yields multiple new particles. As Skaar explained, you end up with a possibility of several photons, or a bunch of photons, with smaller numbers remaining much more likely than huge swarms.

The research team noted that removing the mirror creates a state that is a superposition of possibilities with different numbers of photons, and that while removing the mirror infinitely fast would conjure an infinity of light particles, pulling it away more slowly still results in a possibility of several photons.

In an accompanying commentary, the team explained that this phenomenon occurs because removing the mirror delivers a tug on the quantum field, pulling loose new light particles from empty space, or a vacuum. Daniele Faccio, a physicist at the University of Glasgow in Scotland, initially reacted to the study by calling it nonsense before reviewing the math. Then you read it, and I enjoyed it, he said, The technique is legit.

Measurement Statistics and Potential Quantum Sensor Applications

The study reveals a striking paradox regarding how the truncated state appears depending on the observer’s perspective. If an observer looks at both sides of the mirror setup simultaneously, they witness a complex eruption of countless superposed photons. However, if measurements are taken strictly on either side of the transition region, the results look entirely normal.

Measurements on the left side look exactly like a single-photon state, while the right side appears as a vacuum, separated by a very narrow transition region. Skaar called this outcome really crazy, noting that the complex quantum state produces the exact same measurement statistics as simple states when limited to local observables.

While the study remains purely theoretical, researchers suggest the calculations could inform future work involving quantum sensors. Faccio pointed out that probing the fundamental nature of individual photons might matter because there are funky things that people do with [photons] for sensing and measuring, citing gravitational wave catchers as a primary example.

Future research may also explore whether similar techniques can be applied to other fundamental particles that exhibit wave-like behaviors in quantum physics, such as electrons.