  Quantum conference key agreement (CKA) enables key sharing among multiple
trusted users with information-theoretic security. Currently, the key rates of
most quantum CKA protocols suffer from the limit of the total efficiency among
quantum channels. Inspired by the coherent one-way and twin-field quantum key
distribution (QKD) protocols, we propose a quantum CKA protocol of three users.
Exploiting coherent states with intensity 0 and $\mu$ to encode logic bits, our
protocol can break the limit. Additionally, the requirements of phase
randomization and multiple intensity modulation are removed in our protocol,
making its experimental demonstration simple.
