Duan Luming's group at Tsinghua University achieves the first crosstalk-free double quantum bit encoding between identical ions

The research group of Lu-Ming Duan at the Institute of Cross-Information has recently achieved the first double quantum bit encoding using homogeneous ions that can be coherently converted to overcome the effect of crosstalk between multiple bits during quantum computing. Overcoming the effect of crosstalk is a key requirement for achieving quantum error correction and large-scale fault-tolerant quantum computing, and the breakthrough by Lu-Ming Duan's group provides an important tool for fault-tolerant quantum computing in ion-trap-based systems.

The resulting paper, "Realizing coherently convertible dual-type qubits with the same ion species," was recently published in the prestigious international academic journal Nature Physics, and Professor Hempel of the Swiss ETH was featured in the concurrent Nature The paper was published in the Nature Physics journal, and Prof. ETH (Switzerland) dedicated an article to the results in the News & Reviews section of Nature Physics.

Ion well systems are one of the most promising systems for quantum computing and quantum networks. The other type of bits is used for auxiliary operations such as measurement, cooperative cooling, ion-photon entanglement, etc. and is called "auxiliary bits".

In order to avoid the spontaneous radiation of photons from the auxiliary bits during the auxiliary operations to destroy the quantum information stored in the nearby data bits, previous research on quantum computing in ion traps required two different types of ions to act as the two types of quantum bits. However, it is very challenging to achieve high-fidelity quantum entanglement logic gates between different types of ions.

Schematic diagram of the experimental protocol

To overcome the above difficulties, Lu-Ming Duan's group experimentally encoded these two types of quantum bits (S-qubit and F-qubit) using two pairs of hyperfine structured energy levels of the same (_^171)Yb^+ ion, and achieved the coherent conversion between the two quantum bits with 99.5% fidelity on the microsecond scale using a two-color narrow linewidth laser at 411 nm and 3432 nm. It also demonstrates that the crosstalk error rate of the other quantum bit is less than 0.06%, which is lower than the error rate threshold of about 1% for fault-tolerant quantum computing, when the initial state preparation, measurement, single-bit logic gate, and laser cooling are performed on one of the quantum bits. This technique solves a key difficulty for future large-scale ion quantum computing and quantum networks.

Experimental results of measuring the fidelity of coherent conversion of two types of quantum bits

The corresponding author of the paper is Prof. Lu-Ming Duan of the Institute of Cross-Information, Tsinghua University. Artemisia Xiang Yang, a postdoctoral fellow at the Institute of Cross-Information, Tsinghua University, and Jianyu Ma, a PhD student of the Institute of Cross-Information, Class of 2018, are co-authors of the article. Other authors include Yu-Kai Wu, Assistant Professor of the Institute of Cross-Information, Ye Wang, PhD student of the Institute of Cross-Information, Class of 2019, Ming Cao, Wei-Xuan Guo, Lu Feng, PhD student of the Institute of Cross-Information, Class of 2018, Yuan-Yuan Huang, Assistant Researcher of the Institute of Cross-Information and Zichao Zhou, Associate Researcher. This work was funded and supported by the Tsinghua University Independent Research Program and the National Education Ministry Fund.

Link to the paper:

https://doi.org/10.1038/s41567-022-01661-5