# Contributed Talk 1a

Mon, 2 Sep
, 12:30 - 13:10

- Decoy state quantum key distribution for practical single-photon sourcesRoberto Pousa (University of Strathclyde); Daniel Oi (University of Strathclyde); John Jeffers (University of Strathclyde)[abstract]
**Abstract:**High brightness, low second-order correlation function single-photon sources (SPSs) are an alternative to commonly employed weak coherent pulse (WCP) sources for discrete variable quantum key distribution (QKD) and offer potential key-rate and finite-block scaling advantages. However, the loss tolerance of SPS-based QKD is compromised by photon number splitting (PNS) attacks against non-negligible multiphoton emissions. Decoy state (DS) techniques mitigate against PNS attacks, with WCP-DS QKD over several hundred km in fibre being demonstrated. DS QKD protocols for different source photon number statistics have been proposed, such as for binomial and thermal distributions. Here, we investigate the use of generalised DS techniques assuming we do not have access to the true photon number statistics of the SPS. Thus, we bound the source distribution using the mean photon number and the second-order correlation function, which provides us with enough partial knowledge to compute our decoy SPS protocols. Hence, we provide finite-key security bounds for an SPS-based Efficient BB84 for several decoy protocols with optimised parameters, and derive required SPS characteristics to achieve a key rate enhancement over DS WCPs and match their loss tolerance. - Finite-size decoy-state security proof against coherent attacksShlok Nahar (Institute for Quantum Computing and Department of Physics and Astronomy, University of Waterloo); Lars Kamin (Institute for Quantum Computing and Department of Physics and Astronomy, University of Waterloo); Devashish Tupkary (Institute for Quantum Computing); Yuming Zhao (Institute for Quantum Computing and Department of Pure Mathematics, University of Waterloo); Ernest Y.-Z. Tan (Institute for Quantum Computing and Department of Physics and Astronomy, University of Waterloo); and Norbert Lütkenhaus (Institute for Quantum Computing and Department of Physics and Astronomy, University of Waterloo)[abstract]
**Abstract:**Proving the security of quantum key distribution (QKD) protocols against arbitrary attacks is a challenging task for arbitrary protocols. Here, we accomplish this task by extending and improving both the decoy-state analysis against collective attacks, and the postselection technique to uplift this security proof to arbitrary attacks. First, we improve the postselection technique - both by improving the cost paid for the uplift, and by rigorously showing how it can be applied to generic optical protocols. Second, we fundamentally improve the decoy-state analysis in such a way that we require only one decoy intensity to achieve the same performance as prior analysis with two decoy intensities. This has two consequences - it makes the protocol easier to practically implement, and reduces the penalty incurred by using the postselection technique. Third, we extend the finite-size QKD analysis to decoy-state protocols and generically improve the finite-size correction terms that appear. Thus, we provide a full security proof against arbitrary attacks for generic decoy-state protocols.