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abstract: 'Uhrig’s dynamical decoupling pulse sequence has emerged as one universal and highly promising approach to decoherence suppression. So far both the theoretical and experimental studies have examined single-qubit decoherence only. This work extends Uhrig’s universal dynamical decoupling from one-qubit to two-qubit systems and even to general multi-level quantum systems. In particular, we show that by designing appropriate control Hamiltonians for a two-qubit or a multi-level system, Uhrig’s pulse sequence can also preserve a generalized quantum coherence measure to the order of $1+O(T^{N+1})$, with only $N$ pulses. Our results lead to a very useful scheme for efficiently locking two-qubit entangled states. Future important applications of Uhrig’s pulse sequence in preserving the quantum coherence of multi-level quantum systems can also be anticipated.'
author:
- Musawwadah Mukhtar
- Thuan Beng Saw
- Wee Tee Soh
- Jiangbin Gong
title: 'Universal Dynamical Decoupling: Two-Qubit States and Beyond'
---

Introduction
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Decoherence, i.e., the loss of quantum coherence due to system-environment coupling, is a major obstacle for a variety of fascinating quantum information tasks. Even with the assistance of error corrections, decoherence must be suppressed below an acceptable level to realize a useful quantum operation. Analogous to refocusing techniques in nuclear magnetic resonance 