Cutting a photon in two creates an infinite swarm of particles
By definition, elementary particles can’t be broken into smaller pieces. But in a new theoretical study published in Physical Review Letters, Johannes Skaar and colleagues have revealed what would happen if you tried anyway for a single photon. The answer is deeply strange: attempting to cut a photon in two wouldn’t produce two smaller photons, but instead conjure an infinite number of them out of thin air.
Impossible to cut in half
Like any quantum particle, a photon exists simultaneously as a single, localized particle, and an extended wave, spread out across space. For their investigation, Skaar’s team considered what would happen if a single photon passed through an optical shutter—essentially a very fast mirror that can be switched on and off to block part of a pulse of light. If the shutter was fast enough, it could intercept the photon mid-pulse, snipping off part of this extended wave.
To find out what would happen afterward, the researchers applied quantum equations that describe how the photon’s underlying electromagnetic field behaves at the quantum level. Specifically, their analysis tracked precisely how the photon’s quantum state would be transformed by the shutter’s intervention.
Infinite superposition
Rather than producing a photon on one side and a vacuum on the other, the shutter generates something far more strange and complex: a superposition of states containing infinitely many photons simultaneously.
This happens because, in quantum mechanics, empty space isn’t truly empty—in reality, it seethes with fluctuations in the electromagnetic field. By rapidly switching the shutter, the team found that these fluctuations are disturbed—and in doing so, they spontaneously create new photons. Crucially though, if you were to look only at the region immediately either side of where the shutter operated, the state would appear deceptively normal: indistinguishable from a single photon on one side, and a simple vacuum on the other.
Deeper quantum investigations
The result offers a striking illustration of how quantum particles behave differently from everyday objects, and raises deeper questions about how quantum systems are measured and how information is localized in space. In their future research, Skaar and his colleagues now plan to push further—exploring whether the same bizarre physics would apply when more than one photon is involved, or when the analysis is extended to other elementary particles, such as electrons.
Source: phys.org
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Cutting a photon in two creates an infinite swarm of particles