Postselection technique for optical Quantum Key Distribution with improved de Finetti reductions

Abstract

The postselection technique is an important proof technique for proving the security of quantum key distribution protocols against coherent attacks. In this work, we go through multiple steps to rigorously apply the postselection technique to optical quantum key distribution protocols. First, we place the postselection technique on a rigorous mathematical foundation by fixing a technical flaw in the original postselection paper. Second, we extend the applicability of the postselection technique to prepare-and-measure protocols by using a de Finetti reduction with a fixed marginal. Third, we show how the postselection technique can be used for decoy-state protocols by tagging the source. Finally, we extend the applicability of the postselection technique to realistic optical setups by developing a new variant of the flag-state squasher. We also improve existing de Finetti reductions, which reduce the effect of using the postselection technique on the key rate. These improvements can be more generally applied to other quantum information processing tasks. As an example to demonstrate the applicability of our work, we apply our results to the time-bin encoded three-state protocol. We observe that the postselection technique performs better than all other known proof techniques against coherent attacks.

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• Generalized Numerical Framework for Improved Finite-Sized Key Rates with Rényi Entropy
• A consolidated and accessible security proof for finite-size decoy-state quantum key distribution
• Generalized Rényi entropy accumulation theorem and generalized quantum probability estimation
• Numerical security analysis for quantum key distribution with partial state characterization
• Imperfect detectors for adversarial tasks with applications to quantum key distribution
• Phase error rate estimation in QKD with imperfect detectors
• Quantum Key Distribution with Imperfections: Recent Advances in Security Proofs
• High-dimensional quantum communication with scalable photonic entanglement in time and frequency
• Security proofs for practical QKD: variations, techniques, gaps, and limitations