  The quantum clock synchronization (QCS) is to measure the time difference
among the spatially separated clocks with the principle of quantum mechanics.
The first QCS algorithm proposed by Chuang and Jozsa is merely based on two
parties, which is further extended and generalized to the multiparty situation
by Krco and Paul. They present a multiparty QCS protocol based upon W states
that utilizes shared prior entanglement and broadcast of classical information
to synchronize spatially separated clocks. Shortly afterwards, Ben-Av and Exman
came up with an optimized multiparty QCS using Z state. In this work, we
firstly report an implementation of Krco and Ben-AV multiparty QCS algorithm
using a four-qubit Nuclear Magnetic Resonance (NMR). The experimental results
show a great agreement with the theory and also prove Ben-AV multiparty QCS
algorithm more accurate than Krco.
