We propose a family of sifting-less quantum-key-distribution protocols which use reverse-reconciliation, and are based on weak coherent pulses (WCPs) polarized along m different directions. When m=4, the physical part of the protocol is identical to most experimental implementations of BB84 and SARG04 protocols and they differ only in classical communications and data processing. We compute their total keyrate as function of the channel transmission T, using general information theoretical arguments and we show that they have a higher keyrate than the more standard protocols, both for fixed and optimized average photon number of the WCPs. When no decoy-state protocols (DSPs) are applied, the scaling of the keyrate with transmission is improved from T2 for BB84 to T^(1+1/(m-2)). If a DSP is applied, we show how the keyrates scale linearly with T, with an improvement of the prefactor by 75.96 % for m=4. High values of $ m $ allow to asymptotically approach the keyrate obtained with ideal single photon pulses. The fact that the keyrates of these sifting-less protocols are higher compared to those of the aforementioned more standard protocols show that the latter are not optimal, since they do not extract all the available secret key from the experimental correlations.
We propose a family of sifting-less quantum-key-distribution protocols which use reverse reconciliation, and are based on weak coherent pulses (WCPs) polarized along
m different directions. When
m=4, the physical part of the protocol is identical to most experimental implementations of BB84 [Bennett and Brassard, in Proceedings of the IEEE International Conference on Computers, Systems, and Signal Processing (IEEE, New York, 1984)] and SARG04 [Scarani, Ac\'{\i}n, Ribordy, and Gisin, Phys. Rev. Lett. 92, 057901 (2004); Ac\'{\i}n, Gisin, and Scarani, Phys. Rev. A 69, 012309 (2004)] protocols and they differ only in classical communications and data processing. We compute their total key rate as a function of the channel transmission
T, using general information theoretical arguments, and we show that they have a higher key rate than the more standard protocols, both for fixed and optimized average photon number of the WCPs. When no decoy-state protocols (DSPs) [Hwang, Phys. Rev. Lett. 91, 057901 (2003); Lo, Ma, and Chen, Phys. Rev. Lett. 94, 230504 (2005); Wang, Phys. Rev. A 72, 012322 (2005)] are applied, the scaling of the key rate with transmission is improved from
T2 for BB84 to ${T}^{1+\frac{1}{m\ensuremath{-}2}}$. If a DSP is applied, we show how the key rates scale linearly with
T, with an improvement of the prefactor by 75.96% for
m=4. High values of
m allow one to asymptotically approach the key rate obtained with ideal single-photon pulses. The fact that the key rates of these sifting-less protocols are higher compared to those of the aforementioned more standard protocols show that the latter are not optimal, since they do not extract all the available secret keys from the experimental correlations.
The BB84 protocol is fundamental to quantum-secure communications, yet its extension to multi-receiver networks remains underexplored. This study addresses this gap by implementing a dual-receiver BB84 framework in Qiskit to evaluate security against intercept–resend and photon-number-splitting (PNS) attacks. Our methodology incorporates weak coherent pulses and realistic channel imperfections. Key findings show that intercept–resend attacks induce a detectable (~25%) increase in QBER, while PNS attacks allow a 100% gain in eavesdropper information with less than 2.5% QBER—revealing a critical vulnerability, which highlights the importance of a true single-photon source. The findings emphasize the suitability of BB84 for multiparty QKD scenarios, either as a decoy-state mechanism for enhanced eavesdropping detection or as a direct secure communication protocol.