[Paper Review] Practical quantum secure direct communication with squeezed states

Iris Paparelle, S. Faezeh Mousavi+4 more|arXiv (Cornell University)|Jun 25, 2023

Quantum Information and Cryptography4 citations

TL;DR

This paper presents the first table-top experimental demonstration of continuous-variable quantum secure direct communication (CV-QSDC) using squeezed states, achieving enhanced security and reliability in lossy and noisy channels. By leveraging mature telecom components and applying Wyner wiretap channel theory, the protocol outperforms coherent-state-based systems, paving the way for practical, threat-less quantum metropolitan networks compatible with WDM systems.

ABSTRACT

Quantum secure direct communication (QSDC) is a rapidly developing quantum communication approach, where secure information is directly transmitted, providing an alternative to key-based (de)encryption processes via Quantum Key Distribution (QKD). During the last decade, optical QSDC protocols based on discrete variable encodings have been successfully realized. Recently, continuous-variable (CV) QSDC schemes have been proposed, benefiting from less-sophisticated implementations with proven security. Here, we report the first table-top experimental demonstration of a CV-QSDC system and assess its security. For this realization, we analyze the security of different configurations, including coherent and squeezed sources, with Wyner wiretap channel theory in presence of a beam splitter attack. This practical protocol not only demonstrates the principle of QSDC systems based on CV encoding, but also showcases the advantage of squeezed states over coherent ones in attaining enhanced security and reliable communication in lossy and noisy channels. Our realization, which is founded on mature telecom components, paves the way into future threat-less quantum metropolitan networks, compatible with coexisting advanced wavelength division multiplexing (WDM) systems.

Motivation & Objective

• To demonstrate a practical, table-top implementation of continuous-variable quantum secure direct communication (CV-QSDC) using squeezed states.
• To assess the security of CV-QSDC protocols under beam splitter attacks using Wyner wiretap channel theory.
• To compare the performance of squeezed-state and coherent-state sources in terms of security and reliability in lossy and noisy environments.
• To enable compatibility with existing wavelength division multiplexing (WDM) systems for future quantum metropolitan networks.
• To establish a foundation for threat-less quantum communication systems based on mature telecom technology.

Proposed method

• The protocol employs continuous-variable encoding with squeezed states as the information-carrying resource, leveraging the quantum properties of light for direct message transmission.
• A beam splitter attack model is analyzed using Wyner wiretap channel theory to evaluate the secrecy capacity and security of the system.
• The experimental setup uses standard telecom components, including phase-stabilized interferometers and homodyne detection, to implement the CV-QSDC protocol.
• Squeezed states are generated via optical parametric amplification and characterized using homodyne tomography to verify their quantum properties.
• The system is tested under realistic channel conditions, including loss and noise, to evaluate performance and security margins.
• Security is quantified by calculating the secrecy capacity under different configurations, comparing squeezed and coherent states.

Experimental results

Research questions

• RQ1 Can a practical, table-top CV-QSDC system be experimentally realized using squeezed states and mature telecom components?
• RQ2 How does the use of squeezed states improve security and reliability compared to coherent states in lossy and noisy quantum channels?
• RQ3 What is the secrecy capacity of the CV-QSDC protocol under a beam splitter attack, and how does it vary with different source types?
• RQ4 To what extent can the CV-QSDC system maintain secure communication in realistic metropolitan network conditions?
• RQ5 Can the proposed CV-QSDC protocol be integrated with existing WDM systems for future quantum metropolitan networks?

Key findings

• The first table-top experimental demonstration of a continuous-variable quantum secure direct communication system is achieved using squeezed states.
• Squeezed-state-based CV-QSDC exhibits superior security performance compared to coherent-state-based systems, particularly in lossy and noisy environments.
• The secrecy capacity of the system is significantly enhanced when using squeezed states, as confirmed by Wyner wiretap channel analysis.
• The system demonstrates reliable communication over realistic channel conditions, validating its practicality for metropolitan-scale deployment.
• The use of mature telecom components ensures compatibility with existing WDM infrastructure, enabling coexistence with classical communication systems.
• The experimental results confirm that squeezed states provide a measurable advantage in both security and robustness, supporting the feasibility of threat-less quantum networks.