# Creating nonlocality using geometric phases between partially distinguishable photons

## TL;DR

This paper demonstrates that nonlocal correlations can be generated in a fixed interferometer by manipulating the geometric phases of input photons, using the quantum Zeno effect to overcome interference visibility limitations.

## Contribution

It introduces a novel method to create nonlocality through geometric phases in a fixed interferometer without variable phase shifts or measurement settings.

## Key findings

- Nonlocal correlations are achievable with independent photons via geometric phases.
- A trade-off exists between geometric phases and interference visibility.
- The quantum Zeno effect enables nonlocality with 12 or more photons.

## Abstract

The geometric (Berry-Pancharatnam) phase originates from the intrinsic geometry of the space of quantum states and can be observed in different situations, such as a cyclic evolution of a quantum system. Here, we utilize the geometric phase to obtain a surprising insight: It is possible to create nonlocal correlations in a fixed interferometer with independent photon inputs by varying the photons' internal states.In particular, we consider a cyclic interferometer that is fixed, i.e., that has no variable internal phase shifts or subsequent measurement settings. Instead, the measurement choices of the different parties correspond to the internal states of the input photons which influence the observed correlations via a collective $N$-photon geometric phase, constituting a different approach for the generation of nonlocality with respect to the usual paradigm. We observe a trade-off between the geometric phases and the visibility of the many-photon interference, impeding the generation of nonlocality. However, by making use of the dynamical quantum Zeno effect, we show that nonlocality can be created in the fixed cyclic interferometer using 12 (or more) independent photons.