# Quantum key distribution with simply characterized light sources

## TL;DR

This paper presents a security proof for quantum key distribution that requires minimal assumptions on light sources, simplifying device verification and enhancing practical security.

## Contribution

It introduces a QKD security proof that relaxes many assumptions on light sources, relying only on basic independence and photon number bounds.

## Key findings

- Security proof with minimal source assumptions
- No need for detailed phase modulation characterization
- Enhanced practical security verification

## Abstract

To guarantee the security of quantum key distribution (QKD), several assumptions on light sources must be satisfied. For example, each random bit information is precisely encoded on an optical pulse and the photon-number probability distribution of the pulse is exactly known. Unfortunately, however, it is hard to check if all the assumptions are really met in practice, and it is preferable that we have minimal number of device assumptions. In this paper, we adopt the differential-phase-shift (DPS) QKD protocol and drastically mitigate the requirements on light sources. Specifically, we only assume the independence among emitted pulses, the independence of the vacuum emission probability from a chosen bit, and upper bounds on the tail distribution function of the total photon number in a single block of pulses for single, two and three photons. Remarkably, no other detailed characterizations, such as the amount of phase modulation, are required. Our security proof significantly relaxes demands for light sources, which paves a route to guarantee implementation security with simple verification of the devices.