Key Findings
A theoretical simulation investigated what happens when a photon is 'cut' by a fast-closing shutter, a situation made possible by wave-particle duality.
The results, accepted for publication in Physical Review Letters, indicate that the severed photon does not simply produce a single photon or none, but a mixture of states including zero to infinitely many photons. The expected number of photons becomes infinite only if the shutter closes infinitely fast; for realistic shutter speeds, even a thousand photons would be extremely unlikely.
When measured locally from one side of the shutter, the state appears as a simple single-photon state; from the other side, it appears as a vacuum (no photon). Globally, the state is the complex mixture.
Implications
The team, led by Johannes Skaar of the University of Oslo, suggests this local simplicity versus global complexity raises fundamental questions about particle nature. They plan to extend the analysis to other quantum particles like electrons.
A key motivation is to develop a description of particle interactions with a clear causal relationship, avoiding issues arising from interactions that in current theory stretch over infinite time.
Status
The work is theoretical and accepted in Physical Review Letters. More work is needed to fully develop the framework, but the result is considered an important step toward describing particle interactions with clear causality.