  Twin-Field Quantum Key Distribution (TF-QKD) enables two distant parties to
establish a shared secret key, by interfering weak coherent pulses (WCPs) in an
intermediate measuring station. This allows TF-QKD to reach greater distances
than traditional QKD schemes and makes it the only scheme capable of beating
the repeaterless bound on the bipartite private capacity. Here, we generalize
TF-QKD to the multipartite scenario. Specifically, we propose a practical
conference key agreement (CKA) protocol that only uses WCPs and linear optics
and prove its security with a multiparty decoy-state method. Our protocol
allows an arbitrary number of parties to establish a secret conference key by
single-photon interference, enabling it to overcome recent bounds on the rate
at which conference keys can be established in quantum networks without a
repeater.
