Quantum Keyless Private Communication under intense background noise

TL;DR

This work proposes a variant of quantum keyless private communication using polarization encoding using polarization encoding and experimentally validate both the original on-off keying method and the polarization-multiplexed approach using time-multiplexed threshold single-photon detectors as photon counting detectors.

Abstract

Quantum key distribution relies on quantum mechanics to securely distribute cryptographic keys, offering security but necessitating complex infrastructure and significant resources for practical implementation. Quantum keyless private communication ensures information-theoretic security in free-space communication, with simpler setups, and without the need for secret keys by leveraging the wiretap channel model. Here we propose a variant of quantum keyless private communication using polarization encoding and experimentally validate both the original on-off keying method and the polarization-multiplexed approach using time-multiplexed threshold single-photon detectors as photon counting detectors. Our analysis highlights the advantages of polarization-multiplexed schemes for daylight operation. This work paves the way towards practical and scalable quantum communication systems, with potential applications extending to space-based communication.

Figures (10)

• Figure 1: Experimental setup capable of implementing OOK- and PM-QKPC. PBS: polarizing beam splitter. EOPM: electro-optic polarization modulator. PA: passive attenuator. SPD: single photon detector. $\frac{\lambda}{4}$: quarter-waveplate. $\frac{\lambda}{2}$: half-waveplate. SF: spectral filter. The black dashed arrows are electrical connections.
• Figure 2: QBER values as a function of the received number of photons with $\Delta = 0.03$ ($\approx 1500$ Hz). a) OOK-QKPC. In black we have Eve's QBER for different values of $\gamma$, and the colors show Bob's QBER for different discrimination strategies, different threshold choices, k. b) PM-QKPC. Different colors correspond to different polarization angles between the states. The markers correspond to different discrimination strategies (see Appendix \ref{['appendix: discrimination']}). The shaded area represents a one-degree error in the polarization preparation of the states.
• Figure 3: Heat map of the maximum private capacity as a function of the photon noise, $\Delta$, and the intercepted signal by Eve, $\gamma$. a) OOK encoding, and a fixed threshold choice of $k=1$. b) OOK encoding, and a PNR detection scheme. c) PM encoding.
• Figure 4: Plot of the maximum private capacity as a function of the photon noise, $\Delta$, for $\gamma=0.1$ The different colors correspond to OOK-QKPC without PNR measurements (blue), OOK-QKPC with PNR measurements (red), PM-QKPC (green) and PM-QKPC with limited polarization angle and average number of photons (black).
• Figure 5: Diagram illustrating the notation for a binary communication channel.