'Frequency-modulated' pulsed Bell setup avoids post-selection

TL;DR

This paper introduces a frequency-modulated pulsed Bell setup that eliminates the need for post-selection, simplifying synchronization, enhancing security in QKD, and improving the efficiency of Bell tests.

Contribution

The authors propose a novel frequency modulation technique for pulsed Bell setups that inherently identifies valid coincidences without post-selection, addressing fundamental and practical issues.

Findings

Avoids post-selection in Bell experiments

Robust against clock drift and adversarial attacks in QKD

Optimally identifies entangled pairs without additional synchronization

Abstract

Excepting event-ready setups, Bell experiments require post-selection of data to define coincidences. From the fundamental point of view, post-selection is a true 'logical loophole'. From the practical point of view, it implies a numerically heavy and time consuming task. In Quantum Key Distribution (QKD), it opens vulnerability in case of a hostile adversary. The core of the problem is to synchronize independent clocks during long observation runs. A pulsed source gets rid of clocks' drift, but there is still the problem of identifying the same pulse in each remote station. We use a frequency modulated pulsed source to achieve it. This immediately defines the condition of valid coincidences in a manner that is unaffected by the drift between the clocks. It allows finding the set of entangled pairs avoiding post-selection and in a way that is found to be optimal. It is also robust against a hostile adversary in the case of QKD.