Anti-symmetrization reveals hidden entanglement

TL;DR

This paper demonstrates that anti-symmetrization can reveal hidden entanglement in two-photon systems through anti-bunching at a beamsplitter, extending the concept to frequency-entangled photons and potentially other quantum systems.

Contribution

It introduces a method to detect hidden entanglement via anti-symmetrization and anti-bunching, applicable to various quantum systems beyond traditional measurements.

Findings

Anti-bunching indicates entanglement in specific antisymmetric states.

Experimental demonstration with frequency-entangled photons.

Potential application to atomic ensembles and Bose-Einstein condensates.

Abstract

Two-photon anti-bunching at a beamsplitter is only possible if the photons are entangled in a specific state, anti-symmetric in the spatial modes. Thus, observation of anti-bunching is an indication of entanglement in a degree of freedom which might not be easily accessible in an experiment. We experimentally demonstrate this concept in the case of the interference of two frequency entangled photons with continuous frequency detunings. The principle of anti-symmetrisation of the spatial part of a wavefunction and subsequent detection of hidden entanglement via anti-bunching at a beamsplitter may facilitate the observation of entanglement in other systems, like atomic ensembles or Bose-Einstein condensates. The analogue for fermionic systems would be to observe bunching.