# Advantage in two-way communication using non-classical states of light

## TL;DR

This paper demonstrates that various non-classical states of light, including generalized NOON states, can provide advantages in two-way quantum communication and Bell inequality violations, even under noisy conditions.

## Contribution

It extends the advantage of entangled states in two-way communication to a broader class of non-classical states, including single-mode pure states embedded in entangled states.

## Key findings

- Generalized NOON states achieve maximal advantage in two-way communication.
- Even-coherent NOON states maintain advantage under noisy conditions.
- Certain states violate reference-frame independent Bell inequalities.

## Abstract

The advantage of using a single-photon two-mode entangled state in two-way communication via maximal violation of an inequality associated with the `Guess Your Neighbour's Input' (GYNI) game has been theoretically [Phys. Rev. Lett. 120, 060503 (2018)] as well as experimentally [CLEO FID.4 (OSA, 2018)] established quite recently. We show that such an advantage can also be obtained using any single-mode pure non-classical state embedded in a two-mode pure entangled state, wherein the other mode is the vacuum (henceforth referred to as a generalized NOON state), regardless of the average photon number of the single mode state. For the special cases of the even-coherent, odd-coherent, and squeezed vacuum NOON states, we establish that the advantage is also maximal. We show that the usage of the even-coherent NOON states can provide an advantage under noisy apparatuses (beam splitters and photo detectors). As an aside, we study how some of these states fare in terms of violation of a reference-frame independent Bell-type inequality.