Professor Kihwan Kim’s group in the Center of Quantum Information (CQI), Institute of Interdisciplinary Information (IIIS), Tsinghua University, has recently proposed and successfully demonstrated powerful more than two-qubit quantum gate operations in a trapped ion system. The work “Quantum Simulation of the Quantum Rabi Model in a Trapped Ion” was published on July 24 in Nature. The corresponding authors of the paper are Yao Lu, PhD candidate of IIIS, andProf.Kihwan Kim, associate professor of IIIS. The equally contributed first authors of the work are Yao Lu, Shuaining Zhang and Kuan Zhang, Ph.D. candidates of IIIS.
Nowadays there has been a lot of progress in developing quantum system for quantum computation or quantum simulation so that quantum computers are getting closer to reality. It is the time to find out and fill missing technologies for the practical quantum computation. In principle, the universal quantum computation can be decomposed by single qubit and two-qubit entangling gates, but surely such decomposition is not generally efficient and has exponential overheads in the operation. The development of more efficient multiple qubits, more than two-qubit gates, would be essential for a practical quantum computation. Many theoretical papers have pointed out the usefulness and necessity of such multi-qubit gates. However, no scalable realization of more than two-qubit gate has been demonstrated experimentally.
Figure 1 Usefulness of global entangling gate
In this letter, prof. Kim’s group reported the realization of scalable, more than two-qubit gates in a trapped ion system. Trapped ion system is one of the strong leading candidates for the implementation of practical quantum computers. Recently a blue-print of a trapped ion system scalable up to a few dozens of qubits in a single trap has been proposed and a small programmable quantum computer has been realized following the blue-print. Until now, all the operations in such scalable trapped ion system are based on single qubit and two-qubit gates. The research grouped develop the novel scheme of more than two-qubit gates and experimentally demonstrate the global gates up to 4-qubits as an example. They benchmarked the performance of the operation by observing the fidelity of Bell-state, which is significantly larger than classical bounds.
Figure 2 Ion trap that contains multiple ions for the quantum computation
This experiment was completed by Yao Lu, Shuaining Zhang, and Dr. Wentao Chen, Yangchao Shen, and Jialiang Zhang supported the experiment. Jingning Zhang, Assistant Researcher of IIIS, provided theoretical support for this experiment. This work was supported by the National Key Research and Development Program of China under Grants No. 2016YFA0301900 and No. 2016YFA0301901 and the National Natural Science Foundation of China Grants No. 11574002, and No. 11504197, the National Natural Science Foundation of China.
The paper is available at: https://www.nature.com/articles/s41586-019-1428-4