Realizing quantum advantage without entanglement in single-photon states

TL;DR

This paper demonstrates that quantum advantage can be achieved using single-photon states with quantum discord, without relying on entanglement, through an optical setup for symmetric two-qubit states.

Contribution

It introduces an optical method to realize symmetric two-qubit X-states with controllable quantum discord, enabling quantum advantage without entanglement.

Findings

Maximum quantum advantage without entanglement is 1/3 bit.

Quantum advantage of 0.311 bit achieved with simplified protocol.

States with quantum discord can be generated without initial entanglement.

Abstract

We discuss the realization of quantum advantage in a system without quantum entanglement but with non-zero quantum discord. We propose an optical realization of symmetric two-qubit $X$-states with controllable anti-diagonal elements. This approach does not requires initially entangled states, and it can generate states that have quantum discord, with or without entanglement. We discuss how quantum advantage can be attained in the context of a two-qubit game. We show that when entanglement is not present, the maximum quantum advantage is 1/3 bit. A comparable quantum advantage, 0.311 bit, can be realized with a simplified transaction protocol involving one vs. the three unitary operations needed for the maximum advantage.