Duality in entanglement of macroscopic states of light

TL;DR

This paper explores the duality in entanglement of macroscopic light states, proposing a new setup to test quantum indistinguishability and demonstrating the broader applicability of entanglement duality beyond single-particle systems.

Contribution

It introduces a novel experimental setup to test entanglement duality in macroscopic systems without fixed particle number assumptions.

Findings

Duality in entanglement can be observed in macroscopic light states.

The proposed setup does not require fixed particle number or single-particle assumptions.

Entanglement duality enables conversion of entanglement between different degrees of freedom.

Abstract

We investigate duality in entanglement of a bipartite multi-photon system generated from a coherent state of light. The system can exhibit polarization entanglement if the two parts are distinguished by their parity, or parity entanglement if the parts are distinguished by polarization. It was shown in [PRL 110, 140404 (2013)] that this phenomenon can be exploited as a method to test indistinguishability of two particles and it was conjectured that one can also test indistinguishability of macroscopic systems. We propose a setup to test this conjecture. Contrary to the previous studies using two-particle interference effect as in Hong-Ou- Mandel setup, our setup neither assumes that the tested state is composed of single particles nor requires that the total number of particles be fixed. Consequently the notion of entanglement duality is shown to be compatible with a broader class of physical systems. Moreover, by observing duality in entanglement in the above system one can confirm that macroscopic systems exhibit quantum behaviour. As a practical side, entanglement duality is a useful concept that enables adaptive conversion of entanglement of one degree of freedom (DOF) to that of another DOF according to varying quantum protocols.