The latest Nature issued on Oct 29 published the result from the collaboration between Prof. Du Jiangfeng research group from Modern Physics Department 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.