# State-Independent Quantum Key Distribution with Two-Way Classical Communication

## TL;DR

This paper introduces a novel quantum key distribution protocol that is state-independent, uses two-way classical communication, and does not require basis matching, leveraging a Bell-type inequality for security verification.

## Contribution

It presents a new QKD protocol based on Bell inequalities that is state-independent and involves two-way classical communication, differing from traditional entanglement-based schemes.

## Key findings

- Protocol achieves raw key generation from single-qubit correlations.
- Uses Bell-CHSH inequality form for eavesdropping detection.
- Does not require basis matching between parties.

## Abstract

A quantum key distribution protocol is proposed that is a variation of BB84 that provides raw key generation from correlations that violate a Bell-type inequality for single qubit systems and not entangled pairs. Additionally, it 1) is state-independent, 2) involves two-way classical communication, and 3) does not require basis matching between the two parties. The Brukner-Taylor-Cheung-Vedral (BTCV) time-like form of the Bell-CHSH inequality [C. Brukner, S. Taylor, S. Cheung, V. Vedral arXiv:quant-ph/0402127] is employed as an eavesdropping check; sequential measurements lead to an inequality identical in form to the Bell-CHSH inequality, which relies only on the measurements performed with no regard for the qubit states. We show that this form manifests naturally from the non-commutativity of observables.