# Realization of the tradeoff between internal and external entanglement

## TL;DR

This paper experimentally demonstrates a new entanglement monogamy relation showing that internal and external entanglement in twin photons limit each other, confirming theoretical predictions and advancing understanding of quantum entanglement constraints.

## Contribution

The study provides the first experimental observation of the tradeoff between internal and external entanglement, revealing a new monogamy relation in quantum entanglement.

## Key findings

- Internal and external entanglement limit each other
- Maximal internal entanglement leads to vanishing external entanglement
- Experimental results match theoretical predictions

## Abstract

We experimentally realize the internal and external entanglement tradeoff, which is a new kind of entanglement monogamy relation different from that usually discussed. Using a source of twin photons, we find that the external entanglement in polarization of twin photons, and the path-polarization internal entanglement of one photon, limit each other. In the extreme case, when the internal state is maximally entangled, the external entanglement must be vanishing, that illustrate entanglement monogamy. Our results of the experiment coincide with the theoretical predictions, and therefore provide a direct experimental observation of the internal and external entanglement monogamy relation.