Superdense coding using the quantum superposition principle

TL;DR

This paper demonstrates a superdense coding protocol that leverages quantum superposition of spin and path degrees of freedom in a single particle, enabling transfer of four outcomes without entanglement.

Contribution

It introduces a superdense coding scheme based solely on quantum superposition, expanding the understanding of information transfer without entanglement.

Findings

Transfer of four distinguishable outcomes using superposition

Superdense coding achieved without entanglement resource

Adding more beam splitters does not improve the scheme

Abstract

By sending a classical two-level system, one can transfer information about only \emph{two} distinguishable outcomes. Here we show that in quantum mechanics, using both the spin and path degrees of freedom of a spin-1/2 particle, and a Mach-Zehnder type interferometric arrangement with two suitable Stern-Gerlach detectors, it is possible to transfer information about \emph{four} distinguishable outcomes. This procedure does \emph{not} require using quantum entanglement as a resource as in the well-known protocol of dense coding, but instead hinges entirely on the quantum superposition principle. We also study probabilistic dense coding using our set-up and show that the dense coding scheme using quantum superposition cannot be optimized any further by extending the interferometric arrangement with more beam splitters.