Protection of noisy multipartite entangled states of superconducting
  qubits via universally robust dynamical decoupling schemes
We demonstrate the efficacy of the universally robust dynamical decoupling
(URDD) sequence to preserve multipartite maximally entangled quantum states on
a cloud based quantum computer via the IBM platform. URDD is a technique that
can compensate for experimental errors and simultaneously protect the state
against environmental noise. To further improve the performance of the URDD
sequence, phase randomization (PR) as well as correlated phase randomization
(CPR) techniques are added to the basic URDD sequence. The performance of the
URDD sequence is quantified by measuring the entanglement in several noisy
entangled states (two-qubit triplet state, three-qubit GHZ state, four-qubit
GHZ state and four-qubit cluster state) at several time points. Our
experimental results demonstrate that the URDD sequence is successfully able to
protect noisy multipartite entangled states and its performance is
substantially improved by adding the phase randomization and correlated phase
randomization sequences.
Akanksha Gautam  Arvind Kavita Dorai