Optimized Multi-Party Quantum Clock Synchronization
  A multi-party protocol for distributed quantum clock synchronization has been claimed to provide universal limits on the clock accuracy, viz. that accuracy monotonically decreases with the number n of party members. But, this is only true for synchronization when one limits oneself to W-states. This work shows that usage of Zen-states, a generalization of W-states, results in improved accuracy, having a maximum when \lfloor n/2 \rfloor of its members have their qubits with a |1> value. 
Radel Ben-Av and Iaakov Exman
quant-ph