Hacking Quantum Networks: Extraction and Installation of Quantum Data

TL;DR

This paper investigates quantum hacking in networks, demonstrating that partially entangled probes can outperform maximally entangled ones, and analyzing how multi-user scenarios affect hacking fidelity, with implications for black-hole information recovery.

Contribution

It introduces a framework for quantum hacking with partially entangled probes, derives optimal decoding formulas, and explores multi-user effects on hacking success.

Findings

Partially entangled probes outperform maximally entangled ones in quantum hacking.

Optimal hacking fidelity depends on the ratio of hacking space to user space.

Multi-user scenarios can significantly reduce hacking fidelity, especially with additional parties.

Abstract

We study the problem of quantum hacking, which is the procedure of quantum-information extraction from and installation on a quantum network given only partial access. This problem generalizes a central topic in contemporary physics -- information recovery from systems undergoing scrambling dynamics, such as the Hayden--Preskill protocol in black-hole studies. We show that a properly prepared partially entangled probe state can generally outperform a maximally entangled one in quantum hacking. Moreover, we prove that finding an optimal decoder for this stronger task is equivalent to that for Hayden--Preskill-type protocols, and supply analytical formulas for the optimal hacking fidelity of large networks. In the two-user scenario where Bob attempts to hack Alice's data, we find that the optimal fidelity increases with Bob's hacking space relative to Alice's user space. However, if a third neutral party, Charlie, is accessing the computer concurrently, the optimal hacking fidelity against Alice drops with Charlie's user-space dimension, rendering targeted quantum hacking futile in high-dimensional multi-user scenarios without classical attacks. When applied to the black-hole information problem, the limited hacking fidelity implies a reflectivity decay of a black hole as an information mirror.