Thermal relaxation error on QKD: Effect and A Probable Bypass

TL;DR

This paper investigates the impact of thermal relaxation errors on quantum key distribution protocols BB84 and E91, revealing security vulnerabilities and proposing a modification to BB84 to prevent eavesdropper advantage.

Contribution

It analyzes the effects of thermal relaxation noise on QKD protocols and introduces a modified BB84 protocol that maintains security despite channel noise.

Findings

E91 loses security immediately under thermal relaxation.

BB84's performance degrades to random guessing over time.

Modified BB84 prevents eavesdropper advantage even with channel knowledge.

Abstract

Quantum cryptography was proposed as a counter to the capacity of quantum computers to break classical cryptosystems. A broad subclass of quantum cryptography, called quantum key distribution (QKD), relies on quantum mechanical process for secure distribution of the keys. Quantum channels are inherently noisy, and therefore these protocols will be susceptible to noise as well. In this paper, we study the performance of two QKD protocols - BB84 and E91 under thermal relaxation error. We show that while E91 protocol loses its security immediately due to loss of entanglement, the performance of BB84 protocol reduces to random guessing with increasing time. Next, we consider the action of an Eve on the BB84 protocol under thermal relaxation noise, who is restricted to guessing the outcome of the protocol only. Under this restriction, we show that Eve can still do better than random guessing when equipped with the characteristics of the noisy channel. Finally, we propose a modification of the BB84 protocol which retains the security of the original protocol, but ensures that Eve cannot get any advantage in guessing the outcome, even with a complete channel information.