Performance of BB84 without decoy states under varying announcement structures

Abstract

In phase-randomized weak coherent pulse (WCP) implementations of Quantum Key Distribution (QKD) BB84 protocol, the decoy method is often used to compensate BB84's vulnerability against photon number splitting (PNS) attacks. However, this typically introduces extra complexities and requirements on experimental devices. In this paper, we are therefore interested in phase-randomized WCP implementations without the decoy method. We examine the performance of three QKD protocols with different classical announcement structures, namely BB84, SARG04, and No Public Announcement of Basis (NPAB) BB84, using numerical security proof techniques. We compare secure key rates of the three protocols in asymptotic and finite-size regimes for lossy and noisy channels. The three protocols show different relative advantages depending on the channel behaviour. Canonical BB84 shows robustness against errors and depolarization, SARG04 demonstrates resilience against high loss channels, and NPAB BB84 shows potential advantages against physical misalignment between QKD devices.

Figures (14)

• Figure 1: In NPAB BB84, the only sifting done is Bob announcing no click/click/multi-click.
• Figure 2: Optimized NPAB BB84 protocol states are shifted relative to bases.
• Figure 3: Performance of BB84, SARG04 and NPAB BB84 at 10 dB channel loss when introducing physical misalignment $\theta$ between detectors in the limit $N\rightarrow\infty$. The signal intensity is optimized.
• Figure 4: Key rate versus number of photons used for key calculation in a given pulse (the photon cutoff $K$). Protocols simulated in the asymptotic limit $N\rightarrow\infty$ with 5 dB quantum channel loss and we optimize the choice of intensity of the phase-randomized WCP (mean photon number $\mu$).
• Figure 5: Secret key rate per signal in a loss-only channel for protocols in the asymptotic limit $N \rightarrow\infty$ total signals sent. The signal intensity is optimized. We take $\text{loss} = -10\log_{10}\eta$ in dB.