Simple security proof of twin-field type quantum key distribution protocol

Marcos Curty,Koji Azuma,Hoi-Kwong Lo

doi:10.1038/s41534-019-0175-6

Abstract

Twin-field (TF) quantum key distribution (QKD) was conjectured to beat the private capacity of a point-to-point QKD link by using single-photon interference in a central measuring station. This remarkable conjecture has recently triggered an intense research activity to prove its security. Here, we introduce a TF-type QKD protocol which is conceptually simpler than the original proposal. It relies on the pre-selection of a global phase, instead of the post-selection of a global phase, which significantly simplifies its security analysis and is arguably less demanding experimentally. We demonstrate that the secure key rate of our protocol has a square-root improvement over the point-to-point private capacity, as conjectured by the original TF QKD.

Highlights

There is a tremendous research interest towards developing a global quantum internet,[1,2,3,4,5,6] as this could enable many useful applications of quantum technologies, including, for example, quantum key distribution (QKD),[7,8] blind quantum computing,[9,10] distributed quantum metrology[11,12] and distributed quantum computing.[13]
Suppose that Alice and Bob are separated over a distance L and there is a station C right in the middle between through atnheompt.icTahlisfibceernwtraitlhsttraatniosnmiitstacnocnenepcffiηtffiffie. dIf to Alice (Bob) Alice and Bob implement the original measurement-device-independent QKD (MDI QKD) scheme in this scenario, it is clear that the key rate cannot scale better than η, as this protocol requires that two-photon coincidence events with one photon from Alice and one comparison, TF QKD
From Bob interfere in can provide a key rate the node C. scaling with pInffiηffiffi because it only requires singles, i.e., one photon reaches the node C. This scaling improvement is well-known in the field of quantum repeaters

Summary

Introduction

There is a tremendous research interest towards developing a global quantum internet,[1,2,3,4,5,6] as this could enable many useful applications of quantum technologies, including, for example, quantum key distribution (QKD),[7,8] blind quantum computing,[9,10] distributed quantum metrology[11,12] and distributed quantum computing.[13]. 49 without loss of generality, we shall assume that the node C is under the full control of Eve. After a QKD run, Alice and Bob can estimate the probability distribution pzz(kc, kd | βA, βB) (pxx (kc, kd | bA, bB)) over kc and kd given the choice of βA and βB (bA and bB) and the selection of the Z (X) basis.

Results

Conclusion