Tsinghua University Improves Sensitivity of Quantum Precision Measurements Using Quantum Error Correcting Codes

Sun Luyan's research group from the Institute of Interdisciplinary Information, Tsinghua University, and Zou Changling's research group, University of Science and Technology of China, have used Bose quantum error correction coding for the first time in a superconducting quantum system to improve the sensitivity of quantum precision measurements . The result paper "Quantum-enhanced radiometry via approximate quantum error correction" was recently published online in the journal Nature Communications.

Since the last century, the continuous improvement of measurement accuracy has promoted the development of technology and research in various fields such as biology, medicine, astronomy, and chemistry. Every decibel improvement in measurement accuracy could push the frontiers of research and maybe even open up a new field of research. Most precision measurements utilize spin ensembles or Bose oscillators to detect weak signals. For example, LIGO uses laser interferometers to detect vibrations in space caused by gravitational waves in the universe. Thanks to human efforts, these sensors are approaching their ultimate classical limits.

The quantum information technology developed in recent years utilizes unique quantum effects and is expected to achieve beyond the classical limit of precision measurement accuracy. As a result, quantum precision measurements have been theoretically extensively studied in the past decade. Exotic quantum states have been proposed to improve the information acquisition rate of sensors, and many preliminary experiments have shown their potential for precision measurements. However, these exotic quantum states are fragile due to decoherence effects caused by ambient noise. Similar to the problems faced by other quantum technologies, quantum advantage is thus subject to decoherence, which is difficult to achieve in practice. Although it has been proposed that the coherence of quantum states can be preserved by quantum error correction, it is extremely challenging to combine quantum error correction with quantum precision measurements in practice.

In the past few years, the Superconducting Quantum Research Group of the Quantum Information Center of Tsinghua University has been working on the research of quantum error correction. Recently, they developed methods for approximate quantum error correction and quantum transition tracking, demonstrating for the first time that the precision of quantum precision measurements can be enhanced by approximating Bose quantum error correction encoding.

Figure 1: Schematic diagram of the experimental system

The experimental sample consists of a superconducting qubit coupled with two microwave resonators respectively (as shown in Figure 1). The two microwave resonators with high lifetime are used as the detection cavity, and the one with low lifetime is used as the receiving cavity. In the experiment, the optical field state in the detection cavity is first prepared into a superposition state of different photon states, which is a typical strange quantum state; and then the receiving cavity is used to receive the microwave signal emitted by the external signal source, and pass through the space between the two cavities. The relative phase of the superposition state of the optical field in the detection cavity will accumulate over time; finally, by reading the phase information of the optical field state in the detection cavity, the microwave signal intensity in the receiving cavity can be measured. At the same time, in the process of detection, in order to resist the decoherence effect of the superposition state of the optical field in the receiving cavity caused by the environmental noise, they used the approximate quantum error correction operation many times in a single experiment and could track the number of errors, thereby enhancing the The measurement sensitivity achievable by this quantum precision measurement scheme is shown in Figure 2.

The measurement sensitivity improvement compared to the two-level system is achieved by the superposition of the quantum states |1 ⟩ and |7 ⟩

This experiment is the first work in recent years to use Bose quantum error correction codes to enhance quantum precision measurement, proving that quantum error correction can be used to improve the performance of quantum precision measurement. This scheme can be extended to ion trap systems and emerging quantum acoustic platforms. Different from the traditional application of quantum error correction in quantum information storage, the use of approximate quantum error correction to enhance the accuracy of quantum precision measurement demonstrated by this experiment is a new concept for near-term quantum applications, and provides a future combination of quantum precision measurement and quantum error correction. research provides new ideas.

Dr. Wang Weiting from the Institute of Interdisciplinary Information, Tsinghua University, Chen Zijie, a 2021 doctoral student of the University of Science and Technology of China, and Liu Xinyu, a 2018 direct doctoral student of the Institute of Interdisciplinary Information, Tsinghua University, are the co-first authors of the article. The co-corresponding authors of the paper are Dr. Wang Weiting, researcher Zou Changling and associate professor Sun Luyan. Other authors include Cai Weizhou, Ma Yuwei, Mu Xianghao, Pan Xiaoxuan, Hua Ziyue, Hu Ling, Xu Yuan, Wang Haiyan, Song Yipu, Zou Xubo, etc. This project is supported by the National Key R&D Program, the National Natural Science Foundation of China, the Guangdong Provincial Key Field R&D Program, the Anhui Provincial Leading Project of Quantum Communication and Quantum Computer Major Project, the Guoqiang Research Institute of Tsinghua University, and the Postdoctoral Fund.

Paper link:

https://www.nature.com/articles/s41467-022-30410-8