Detector decoy quantum key distribution

TL;DR

This paper introduces a simple method to estimate photon number statistics using threshold detectors and a variable attenuator, enhancing quantum key distribution security without complex models.

Contribution

It presents a novel detector decoy technique that simplifies photon number estimation and proves security of entanglement-based QKD with untrusted sources.

Findings

Enables security proof without squash model

Allows discarding double click events without security loss

Demonstrates improved performance in BB84 and 6-state protocols

Abstract

Photon number resolving detectors can enhance the performance of many practical quantum cryptographic setups. In this paper, we employ a simple method to estimate the statistics provided by such a photon number resolving detector using only a threshold detector together with a variable attenuator. This idea is similar in spirit to that of the decoy state technique, and is specially suited for those scenarios where only a few parameters of the photon number statistics of the incoming signals have to be estimated. As an illustration of the potential applicability of the method in quantum communication protocols, we use it to prove security of an entanglement based quantum key distribution scheme with an untrusted source without the need of a squash model and by solely using this extra idea. In this sense, this detector decoy method can be seen as a different conceptual approach to adapt a single photon security proof to its physical, full optical implementation. We show that in this scenario the legitimate users can now even discard the double click events from the raw key data without compromising the security of the scheme, and we present simulations on the performance of the BB84 and the 6-state quantum key distribution protocols.