arXiv subjects

Saif Al Kuwari

Publications and source records attributed to Saif Al Kuwari.

3 recordsLinked to original sources

arXiv2026

One-Sided Device-Independent Quantum Key Distribution over Noisy Metropolitan Links: Noise Thresholds and Purification-Assisted Recovery

One-sided device-independent quantum key distribution (1SDI-QKD) offers a practical middle ground between fully device-independent protocols and standard QKD, achieving security with detection efficiencies as low as 50.1\% on the untrusted side. However, prior analyses assumed idealized channels. This work extends the 1SDI-QKD framework to amplitude damping, dephasing, and depolarizing noise. Results reveal a clear noise hierarchy: dephasing tolerates the most noise before security is lost ($p_{\text{crit}} \approx 0.50$ versus 0.449 and 0.220 respectively), while depolarizing noise imposes the most stringent detection efficiency requirements, exceeding 97\% at 20\% noise where amplitude damping requires 76\%. Security is lost while substantial entanglement remains ($C \approx 0.67$--$0.74$), demonstrating that steering violation, not merely entanglement, determines 1SDI-QKD security. Integrating the BBPSSW purification protocol shows that it functions primarily as a range-extension mechanism: five rounds extend dephasing-limited operation from 10~km to 36~km at 90\% detection efficiency. Accounting for both the $2^n$ pair cost and the cumulative success probability, the effective rate peaks at $ 10^{-3}$ bits per initial pair for dephasing but only $ 10^{-6}$ for amplitude damping and depolarizing noise, identifying phase noise limited links as the regime where purification is worthwhile.

quant-ph↗

arXiv2026

Recovery-Induced Erasure Attack on QKD Systems

Detector dead time is typically treated as a fixed parameter in quantum key distribution (QKD) security analyses. In practice, however, the effective recovery time of single-photon avalanche photodiodes (SPADs) depends on the incident count rate. In this work, we demonstrate that this count-rate-dependent recovery nonlinearity constitutes a distinct attack primitive. We experimentally characterize the dead time shift of a free-running SPAD under controlled broadband loading and observe a substantial increase in effective recovery time as the detected rate rises into the high photon count regime. We show that recovery-induced availability reduction can be modeled as an adversarial erasure channel and derive a conservative bound on the signal detection probability under loading. Unlike previously studied detector-control or efficiency mismatch attacks, the proposed mechanism does not rely on deterministic blinding or timing discrimination. Instead, count-rate-dependent recovery asymmetry induces basis-dependent suppression of detection probabilities ($p_\perp<p_\parallel$), converting mismatch-induced errors into loss. Particularly, we show in active-basis BBM92 systems, this effect reduces the observed quantum bit error rate (QBER) below the abort threshold while increasing erasure probability. Using experimentally measured detector recovery data, we quantify the parameter regime in which such stealth suppression is achievable. These results establish count-rate-dependent detector recovery as a security-relevant vulnerability and show that countermeasures designed for timing-based efficiency mismatch do not directly address recovery-induced erasure (RIE) attack. Our findings underscore the need to incorporate detector recovery dynamics explicitly into practical QKD security models.

quant-ph↗

arXiv2024

Superdense Coding using Bragg Diffracted Hyperentangled Atoms

Superdense coding (SDC) is a popular protocol demonstrating the potential of using quantum mechanics to transfer data, where The sender (Alice) can transfer 2 bits of classical information over a single qubit. We present a scheme for quantum superdense coding through Bragg diffracted hyperentangled atoms generated using cavity quantum electrodynamics (QED). In our scheme, Alice transfers 2 bits of classical information over a single hyperentangled atom. This is achieved by introducing multiple quantum gates using resonant and off-resonant Bragg diffraction in cavity QED setup. This scheme uses multiple degrees of freedom to add an extra layer of security to the encoded information.

quant-ph↗