Evolution of different orders of coherence of a three-qubit system and their protection via dynamical decoupling on an NMR quantum processor

TL;DR

This paper investigates the dynamics of different coherence orders in a three-qubit NMR system under noise and demonstrates tailored dynamical decoupling sequences to effectively preserve specific coherence orders and entanglement.

Contribution

It introduces modified dynamical decoupling sequences tailored for preserving different coherence orders in a three-qubit NMR system, enhancing quantum state protection.

Findings

Third-order coherence is effectively protected with simultaneous DD sequences.

Modified DD sequences successfully preserve zero and second-order coherence.

Two-qubit entanglement can be protected using these DD schemes.

Abstract

We generate different orders of quantum coherence in a three-qubit NMR system and study their dynamics in the presence of inherent noise. Robust dynamical decoupling (DD) sequences are applied to preserve the different coherence orders. Initially, DD sequences are implemented simultaneously on all three spins, which effectively protects third-order coherence; however, other coherence orders decay rapidly instead of being preserved. The robust DD sequences were suitably modified in order to preserve other coherence orders. These sequences are applied to the two participating qubits that generate each zero and second order coherence, ensuring their effective preservation. In contrast, first-order coherence is preserved more efficiently when DD sequences are applied exclusively on the qubit responsible for generating it. Instead of performing full state tomography, coherence orders are measured directly using single pulses. The robust DD protection schemes are finally applied to successfully protect two-qubit entanglement in three-qubit star states.