Measurement-device-independent quantum secure direct communication based on decoy states and polarization–spatial hyperentanglement
TL;DR
An MDI-QSDC protocol based on active three-intensity decoy states and polarization–spatial hyperentanglement is proposed, which exhibits a higher secrecy rate lower bound than three reconstructed decoy-state QSDC references in the low-loss regime.
Abstract
Quantum secure direct communication (QSDC) can directly transmit confidential messages without pre-distributing secret keys. In practical applications, non-ideal light sources naturally contain multiphoton components, which can enable photon number splitting and quantum storage attacks and therefore hinder secure deployment. Existing measurement-device-independent (MDI) QSDC protocols are mostly developed under idealized source assumptions and do not explicitly certify the confidential contribution of practical single-pair emissions. This paper proposes an MDI-QSDC protocol based on active three-intensity decoy states and polarization–spatial hyperentanglement. The protocol directly bounds the accepted two-single-pair contribution from complete two-round statistics, assigns no positive confidential contribution to uncertified multipair events, and uses private Pauli masking together with a stochastic pre-transmission encoder under the stated collective attack model. Polarization–spatial hyperentangled encoding provides a four-bit alphabet for each exact label HBSA event, while the MDI architecture removes the need to trust the measurement device. Under the declared architecture-aware benchmark, the proposed protocol exhibits a higher secrecy rate lower bound than three reconstructed decoy-state QSDC references in the low-loss regime. This numerical advantage is conditional on the stated source, HBSA module, memory, asymptotic decoy state, and collective Pauli assumptions and is not claimed as a universal fourfold improvement.