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Progress in Quantum Control of Spins in Solid-state

A universal set of high-fidelity quantum gates at the threshold for fault-tolerant quantum computations in the NV center system have been realized by Prof. DU Jiangfeng’s group from University of Science and Technology of China. The results stand for the state-of-art high-fidelity control of solid-state spins underambient conditions. This work is published with the title "Experimental fault-tolerant universal quantum gates with solid-state spins under ambient conditions"on Nature Communications on November 25 [Nature Communications 6, 8748 (2015)].

Quantum computation provides great speedup over its classical counterpart for certain problems, since quantum superposition principle makes it possible to executelots of computing tasks simultaneously.One of the key challenges for quantum computation is to realize precise control of the quantum system in the presence of noise. Quantum error correction (QEC) is an effective method to fight against the noisy environment and to realize fault-tolerant quantum computation. Physical Review Letters reported in February 2014 that Du’s group utilized dynamically-corrected gates to suppress the dephasingnoiseduring the gate operations [1]. They have demonstrated single-qubit quantum logic gate operation with a fidelity of up to 0.996. In April of the same year, Nature reported a fidelity of 0.9992 single-qubit quantum logic gate operation on superconducting qubits by Martinis’ group from University of California Santa Barbara, the United States[2].

In order to minimize the error rate of quantum logic gates, a higher accuracy of logic gates is required for suppressing noises more effectively. Du’s group develops a novel composite pulse technique to suppress decoherence and the noises during the single-qubit gates. Several errors that limit the fidelity of quantum gates have been quantitatively characterized and effectively suppressed. With new composite pulses, they have realized single-qubit gate with fidelity up to 0.999952 on a single electron spin in diamond. A modified optimal control method has been further developed to design the control pulse for the CNOT gate, which achieves a gate fidelity of 0.992. Thus, they have successfully demonstrated a universal set of quantum gates with the fault-tolerant control fidelity in a solid-state spin system.

The results stand for the state-of-art high-fidelity control of solid-state spins under ambient conditions, which lays a foundation for realizing fault-tolerant quantum computation in solid spin systems.

This work is supported by National Natural Science Foundation, Ministry of Science and Technology, the Chinese Academy of Sciences and Ministry of Education.

Reference

[1] PRL 112, 050503 (2014)

[2] Nature 508, 500-503 (2014)

(RuiYing,School of Physical Science)