Use of Non-Maximal entangled state for free space BBM92 quantum key distribution protocol

TL;DR

This paper investigates how using non-maximally entangled states affects the security and efficiency of satellite-based BBM92 quantum key distribution, establishing bounds and relationships with Bell inequality violations.

Contribution

It introduces a lower bound on non-maximality for secure key extraction and links Bell violation extent to quantum bit error rate in satellite quantum communication.

Findings

Lower bound on non-maximality for security

Linear relationship between Bell violation and QBER

Enhanced understanding of non-maximal entanglement effects

Abstract

Satellite-based quantum communication for secure key distribution is becoming a more demanding field of research due to its unbreakable security. Prepare and measure protocols such as BB84 consider the satellite as a trusted device, fraught with danger looking at the current trend for satellite-based optical communication. Therefore, entanglement-based protocols must be preferred since, along with overcoming the distance limitation, one can consider the satellite as an untrusted device too. E91 protocol is a good candidate for satellite-based quantum communication; but the key rate is low as most of the measured qubits are utilized to verify a Bell-CHSH inequality to ensure security against Eve. An entanglement-based protocol requires a maximally entangled state for more secure key distribution. The current work discusses the effect of non-maximality on secure key distribution. It establishes a lower bound on the non-maximality condition below which no secure key can be extracted. BBM92 protocol will be more beneficial for key distribution as we found a linear connection between the extent of violation for Bell-CHSH inequality and the quantum bit error rate for a given setup.