# Channel capacity enhancement with indefinite causal order

## TL;DR

This paper investigates whether quantum superposition and quantum switch are the same resource for enhancing classical communication capacity, finding superposition always helps while the switch can be beneficial or detrimental.

## Contribution

It demonstrates through simulations that quantum superposition consistently enhances capacity, whereas the quantum switch's effect varies, revealing different underlying quantum resources.

## Key findings

- Quantum superposition always increases communication capacity.
- Quantum switch can both increase or decrease capacity.
- The difference is due to superposition and non-commutativity effects.

## Abstract

Classical communication capacity of a channel can be enhanced either through a device called a 'quantum switch' or by putting the channel in a quantum superposition. The gains in the two cases, although different, have their origin in the use of a quantum resource, but is it the same resource? Here this question is explored through simulating large sets of random channels. We find that quantum superposition always provides an advantage, while the quantum switch does not: it can either increase or decrease communication capacity. The origin of this discrepancy can be attributed to a subtle combination of superposition and non-commutativity.