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China's top ten Sci-Tech breakthroughs in 2009 :Chinese scientists’ breakthrough in quantum computer research
2010-01-22

563 academicians from the Chinese Academy of Sciences (CAS) and Chinese Academy of Engineering (CAE ) reviewed big achievements made by Chinese and abroad scientists in 2009 and decided on top ten science and technology breakthroughs within and without China. Their choices were released on January 20, 2010. 

 Ranging from the first, China's top ten Sci-Tech breakthroughs are:
1. China’s first Petaflop supercomputer developed by the National University of Defense Technology,
2. China established its first inland Antarctic research station,
3. China's biggest large-scale scientific facility SSRF completed,
4. Chinese scientists’ breakthrough in quantum computer research,
5. China producing world's first approved swine flu vaccine,
6. Chinese scientists created world's first cloned mouse from iPS cells,
7. China developed sodium-sulfur battery with high energy density,
8. Dinosaur fossils uncovered in north-eastern China display the earliest known feathers,
9. Silicon purification by a New Type of Solar Furnace,
10. Industrial demonstration of the synthesis of ethylene glycol from coal.

Professor Du Jiangfeng and his research group made a great breakthrough in quantum computing

The latest Nature issued on Oct 29 published the result from the collaboration between Prof. Du Jiangfeng research group from HFNL of USTC and Prof. Liu Renbao from CUHK. They have successfully used electron spin resonance (ESR) to achieve optimal dynamical decoupling through solid-state experiments for the first time the international community. This greatly improved the coherence time of electronic spin, and effectively preserved electron spin coherence in solids. These achievements are vital to pushing the realization of practical solid-state spin quantum computing.

"News and Views” of Nature has also published a special article entitled“Quantum information: Caught at the finishing line”, which pointed out that “Quantum systems habitually leak information, limiting their usefulness for practical applications.” “By optimally reversing the leak, this information loss has been reduced to a trickle in the solid  state.”“Quantum control schemes such as that us ed by Du and colleagues should prove to be a valuable asset in understanding and attacking the decoherence of quantum information. These achievements are vital to pushing the performance of real, physical systems closer to that required for practical quantum computing.”

It is a great challenge to combine quantum mechanics with computer science and realize quantum computing. Realization of quantum computing highly relies on quantum coherence. However, coupling interference is inevitable in reality, which made quantum coherence fade over time. To exploit the quantum coherence of electron spins in solids in future technologies such as quantum computing, it is vital to overcome the problem of spin decoherence due to their coupling to the noisy environment.

Physicists have put forward many ways to combat decoherence, among which optimal dynamical decoupling is the most promising strategy.  It relies on repeatedly flipping the spins at well-defined intervals of time. The decohering mechanisms in the system reverse in sign when the spins are flipped, allowing most of the decoherence to simply subtract itself away.

Du and colleagues use pulsed electron paramagnetic resonance to demonstrate experimentally optimal dynamical decoupling for preserving electron spin coherence in irradiated malonic acid crystals at temperatures from 50 K to room temperature. Using a seven-pulse optimal dynamical decoupling sequence, they prolonged the spin coherence time to about 30 s; it would otherwise be about 0.04 s without control or 6.2 s under one-pulse control. Optimal dynamical decoupling may be applied to other solid-state systems, and so lay the foundation for quantum coherence control of spins in solids at room temperature.

Once the decoherence mechanisms in solid-state systems are fully known, high-precision coherent control will become easier. Then the realization of quantum computer will no longer be distant.

Preserving electron spin coherence in solids by optimal dynamical decoupling
Nature 461, 1265-1268 (29 October 2009) | doi:10.1038/nature08470; Received 17 June 2009; Accepted 27 August 2009
To exploit the quantum coherence of electron spins in solids in future technologies such as quantum computing, it is first vital to overcome the problem of spin decoherence due to their coupling to the noisy environment. Dynamical decoupling, which uses stroboscopic spin flips to give an average coupling to the environment that is effectively zero, is a particularly promising strategy for combating decoherence because it can be naturally integrated with other desired functionalities, such as quantum gates. Errors are inevitably introduced in each spin flip, so it is desirable to minimize the number of control pulses used to realize dynamical decoupling having a given level of precision. Such optimal dynamical decoupling sequences have recently been explored. The experimental realization of optimal dynamical decoupling in solid-state systems, however, remains elusive. Here we use pulsed electron paramagnetic resonance to demonstrate experimentally optimal dynamical decoupling for preserving electron spin coherence in irradiated malonic acid crystals at temperatures from 50 K to room temperature. Using a seven-pulse optimal dynamical decoupling sequence, we prolonged the spin coherence time to about 30 mus; it would otherwise be about 0.04 mus without control or 6.2 mus under one-pulse control. By comparing experiments with microscopic theories, we have identified the relevant electron spin decoherence mechanisms in the solid. Optimal dynamical decoupling may be applied to other solid-state systems, such as diamonds with nitrogen-vacancy centres, and so lay the foundation for quantum coherence control of spins in solids at room temperature.
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Quantum information: Caught at the finishing line

 

 


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