Quantum 2025 – scientific programme

Parts | Days | Selection | Search | Updates | Downloads | Help

MON: Monday Contributed Sessions

MON 7: Foundational / Mathematical Aspects – Quantum Measurement

MON 7.6: Talk

Monday, September 8, 2025, 15:30–15:45, ZHG008

Which-way knowledge increase via feed-forward of the interfering particle's phase — •Elisabeth Meusert, Marc-Oliver Pleinert, and Joachim von Zanthier — Friedrich-Alexander Universität, Erlangen, Germany

Complementarity constitutes a central aspect of quantum theory. It manifests itself for example in a two-way interferometer, where the simultaneous observation of an interference pattern and the aquisition of which-way information are limited by an inequality, known as the duality relation.

We investigate which-way information in a double-slit interferometer. We find that, depending on the which-way detector observable chosen, the which-way information can be correlated to the interfering particle's phase at the interferometer screen, leading to a phase-dependent which-way knowledge. In specific cases, this knowledge can locally exceed the limit set by the duality relation. Based on this observation, we propose a delayed choice protocol that aims at maximizing the which-way information locally for each phase after the particle has been read out. This allows us to surpass the duality relation limit on phase-average. We present analytical results as a proof of principle of our protocol as well as numerical outcomes quantifying the amount of achievable which-way knowledge.

Keywords: Which-way information; Wave-particle duality; Complementarity; Feed-forward