Sensitivity reaches fT! The University of Science and Technology of China proposed and verified the Floquet quantum amplifier for the first time

Peng Xinhua's research group from the Key Laboratory of Microscopic Magnetic Resonance, Chinese Academy of Sciences, University of Science and Technology of China has made important progress in the field of spin quantum precision measurement. For the first time, the Floquet spin quantum amplification technology has been proposed and verified. Due to the limitation of amplification, quantum amplification of multi-band extremely weak magnetic field signals has been realized, and the sensitivity has reached the level of Femto-Tesla . The related research results were published online in the famous international academic journal "Physical Review Letters" under the title "Floquet Spin Amplification" on June 9 [Phys. Rev. Lett. 128, 233201 (2022)], and was selected as "Editor" Editors' Suggestion" article.

Modern natural science and material civilization have developed along with the continuous improvement of measurement accuracy. With the development of basic research on quantum mechanics and science and technology, quantum enhancement and amplification of weak signals can be achieved through physical systems such as atoms, molecules, and spins. Compared with the traditional amplification technology based on classical circuits, quantum enhanced amplification is limited by lower quantum noise and has higher amplification gain, which provides a powerful research method for improving measurement accuracy, so it has received extensive attention and research. .

At present, quantum amplification technology has played an irreplaceable role in many measurement processes, resulting in many revolutionary achievements, such as masers, lasers, atomic clocks, and even the first discovery of the cosmic microwave background radiation. Awarded multiple times in related fields. However, the current exploration of quantum amplification precision measurement technology is still limited. The realization of signal amplification mainly depends on the discrete energy level transition inherent in the quantum system. Due to the limitation of tunability, the inherent discrete transition frequency of the quantum system often cannot meet the operating frequency required for amplification. Therefore, the performance of quantum amplifiers, such as operating bandwidth, frequency and gain, is limited. If the above difficulties can be overcome, the performance of quantum amplification technology will be greatly improved, which is of great significance for basic physics and practical applications such as the detection of extremely weak electromagnetic waves and exotic particles.

Schematic diagram of the results: (a) Floquet level; (b) schematic diagram of the Flqouet quantum spin amplifier; (c) magnetic detection sensitivity.

In response to the above problems, the researchers proposed the Floquet spin quantum amplification technology, which successfully overcomes the limitations of the previous detection frequency range and other limitations, and realizes the amplification of extremely weak magnetic fields at multiple frequencies. This technique benefits from the group's previously proposed "spin amplification technique" [Nat.Phys. 17, 1402 (2021)] and "Floquet modulation technique" [Sci. Adv. 7(8), eabe0719 (2021)] , organically combine the two, so as to extend the quantum amplification technology to the Floquet spin system: use the Floquet modulation technology to control the energy level and quantum state of the spin, and modify the inherent two-level system (such as 129Xe nuclear spin) into a period The Floquet system has many unique properties, so that the system forms a series of Floquet energy levels with equal energy spacing distribution, and resonance transitions can occur between these energy levels (as shown in the figure above), thus effectively expanding the magnetic field amplification. frequency range. Through theoretical calculations and experimental studies, it is demonstrated for the first time that the Floquet system can achieve simultaneous quantum amplification of two orders of magnitude of the magnetic field to be measured at multiple frequencies, and the measurement sensitivity reaches the femto-Tesla level. This work extends the quantum amplification technology to the Floquet spin system for the first time, and is expected to be further extended to other quantum amplifiers to realize a new class of quantum amplifiers - "Floquet quantum amplifiers".

Peng Xinhua's research group has long been aiming at the field of quantum precision measurement, using quantum precision measurement technology to solve cutting-edge scientific problems in the world. Including the self-developed ultra-sensitive atomic magnetometer in 2018, and using this technology to realize a new type of nuclear magnetic resonance technology that does not require a magnetic field - "zero magnetic field nuclear magnetic resonance" [Sci. Adv. 4(6), eaar6327 (2018)]; Develop a new atomic magnetometer technology from 2019 to 2020 [Adv. Quantum Technol. 3, 2000078 (2020), Phys. Rev. Applied 11, 024005 (2019)], reaching the international leading level of magnetic field detection sensitivity; by further Research, a new type of spin maser will be realized in 2021, creating the best magnetic detection sensitivity in the world at low frequency [Sci. Adv. 7(8), eabe0719 (2021)]. After that, the research group used the developed platform-type quantum precision measurement technology to find new particles beyond the standard model, and achieved a series of research results that have substantially contributed to the development of the discipline. Including the use of a new quantum spin amplifier to search for candidate particles of dark matter in 2021, breaking the internationally recognized strongest cosmic astronomical boundary for the first time [Nat.Phys. 17, 1402 (2021)], and realizing a new class of interactions beyond the Standard Model Ultrasensitive test of the effect, the experimental limit is at least 2 orders of magnitude higher than the previous international best level [Sci. Adv. 7, eabi9535 (2021)].

Associate researcher Jiang Min and doctoral students Qin Yushu and Wang Xin of the Key Laboratory of Microscopic Magnetic Resonance of the Chinese Academy of Sciences are the co-first authors of the paper, and Professor Peng Xinhua is the corresponding author of the paper. The research was funded by the Ministry of Science and Technology, the National Natural Science Foundation of China and Anhui Province.

Paper link:

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.128.233201

Quantum spin amplification technical paper link:

https://www.nature.com/articles/s41567-021-01392-z