Theoretical physicists from the University of Oslo have determined that attempting to “cut” a single photon in half using a high-speed mirror system would result in a quantum state containing a superposition of photons up to infinity, according to a study published July 15, 2026, in Physical Review Letters.
In the standard model of physics, photons are elementary particles and are therefore indivisible. There is no such thing as half a photon. However, because light also behaves as an extended wave packet with a spatial distribution, researchers led by Johannes Skaar explored a quantum shortcut: what happens if you physically truncate that wave?
The team modeled a scenario where a single photon travels toward a mirror. As the leading edge of the photon’s wave packet reflects and begins moving backward, the mirror is suddenly removed. This action effectively cuts away a part of the photon, leaving the remaining portion of the wave to continue forward.
The Vacuum Tug and Infinite Photons
The results defy Newtonian intuition. Rather than producing two smaller photons or a mix of a photon and a vacuum, the process creates a complicated state involving photon numbers up to infinity
, according to the researchers in the paper titled “Truncated Photon.”
This phenomenon is rooted in quantum field theory. The researchers found that a single photon’s waveform cannot maintain a “sharp edge” like the one created by an abrupt mirror removal. To resolve this, the sudden change in the quantum-field modes exerts a tug on the quantum field
, which pulls photons out of the nearby vacuum to form that edge. The sharper the edge, the more photons are superposed.
Removing the mirror creates a state that is, in principle, a superposition of infinitely many photon-number terms, with realistic removals producing a finite, detectable excess of photons above what would be expected, as the researchers and team members noted.
The scale of this effect depends on the speed of the mirror’s removal. While an instantaneous removal would theoretically conjure an infinity of particles, slower, experimentally feasible scenarios would produce a smaller, though still detectable, number of photons.
The Measurement Paradox: Single Photons vs. Bajillions
One of the most counterintuitive aspects of the study is how this “infinite” state appears to an observer.
Nonlinear Events and Quantum Sensors
The study highlights the difference between linear and nonlinear processes. Most light interactions are linear, meaning photons do not typically divide or combine. However, the sudden removal of a mirror during reflection is a nonlinear event. To achieve this in a laboratory, researchers would likely need an optical shutter—mirrors moving at extreme speeds—to catch a photon mid-pulse.
While the current work is theoretical, it may have practical implications for high-precision technology. Daniele Faccio, a physicist at the University of Glasgow, suggested the findings might matter for sensing and measuring, specifically in fields that utilize quantum sensors like gravitational wave detectors.
Next Steps for the University of Oslo Team
The Oslo team views this as a starting point for exploring how information is contained within space and how quantum systems are measured. Because the experimental design is not overly complex, the researchers believe it is possible for experimentalists to replicate these calculations in a real-world setting.
Going forward, Skaar and his colleagues intend to investigate whether similar conditions could produce unusual physics when involving more than one photon.
