Operational effects of the UNOT gate on classical and quantum correlations

TL;DR

This paper investigates how the quantum UNOT gate influences classical and quantum correlations, revealing it preserves classical correlations but can alter quantum discord, violating data processing inequalities, demonstrated experimentally with trapped ions.

Contribution

It uncovers the effects of the UNOT gate on correlations, showing preservation of classical but potential non-local changes in quantum discord, with experimental validation.

Findings

UNOT preserves classical correlations

UNOT can non-locally modify quantum discord

Experimental demonstration with trapped Yb ion

Abstract

The NOT gate that flips a classical bit is ubiquitous in classical information processing. However its quantum analogue, the universal NOT (UNOT) gate that flips a quantum spin in any alignment into its antipodal counterpart is strictly forbidden. Here we explore the connection between this discrepancy and how UNOT gates affect classical and quantum correlations. We show that while a UNOT gate always preserves classical correlations between two spins, it can non-locally increase or decrease their shared discord in ways that allow violation of the data processing inequality. We experimentally illustrate this using a multi-level trapped \Yb ion that allows simulation of anti-unitary operations.