Research Highlights

• Subject Category:
  • Physics

Published online: 4 November 2009 | doi:10.1038/nchina.2009.215

Quantum physics: Coherence control

Felix Cheung

Introduction

© (2009) Nature

Quantum computing uses quantum properties, such as coherence, to process information. Electron spins in solids are ideal for representing qubits (the basic units of quantum information), but they tend to lose coherence — and therefore information — as they interact with the environment. Jiangfeng Du at the University of Science and Technology of China in Hefei, Renbao Liu at the Chinese University of Hong Kong and co-workers¹ have used an approach known as dynamical decoupling to preserve spin coherence in solids.

Dynamical decoupling reduces the random effects of the environment by flipping the electron spins from time to time, a process similar to the well-established 'spin echo' in nuclear magnetic resonance. However, as each spin flip introduces errors into the system, using an optimum number of control pulses is crucial to the success of dynamical decoupling.

In their experiment, the researchers used pulse electron paramagnetic resonance to preserve spin coherence in irradiated malonic acid crystals (pictured) at temperatures from 50 K to room temperature. They used a seven-pulse sequence to prolong the spin coherence time to about 30 microseconds. In comparison, the spin coherence could be maintained for only about 0.04 microseconds without coherence control, and 6.2 microseconds with a one-pulse sequence.

Dynamical decoupling is also applicable to other solid-state systems, such as diamonds with nitrogen-vacancy centres, laying the foundation for the quantum coherence control of spins in solids at room temperature.

The authors of this work are from:
Hefei National Laboratory for Physical Sciences at Microscale and Department of Modern Physics, University of Science and Technology of China, Hefei, China; Department of Physics, Chinese University of Hong Kong, Hong Kong, China.

Reference

1. Du, J. et al. Preserving electron spin coherence in solids by optimal dynamical decoupling. Nature 461, 1265–1268 (2009). | Article