New spin-based quantum amplification technology achieves sensitivity at the level of one flytesla

A research group led by Professor Peng Xinhua from the Key Laboratory of Microscopic Magnetic Resonance, Chinese Academy of Sciences, at the University of Science and Technology of China has made significant progress in the field of precision quantum spin measurement. They have, for the first time, proposed and verified Floquet spin quantum amplification technology, achieving a sensitivity of the femto-tesla level. The findings were recently published online in *Physical Review Letters* and selected as an ‘Editor’s Choice’ article.

With the advancement of fundamental research in quantum mechanics and the development of science and technology, quantum-enhanced amplification of weak signals can be achieved through physical systems such as atoms, molecules and spins. Compared with traditional amplification techniques based on classical circuits, quantum-enhanced amplification technology features lower quantum noise and higher amplification gain, providing a powerful research tool for improving measurement accuracy; it has therefore attracted widespread attention.

However, current exploration of precision measurement techniques for quantum amplification remains limited, with signal amplification primarily relying on the intrinsic discrete energy-level transitions of quantum systems. Due to limitations in tunability, the frequencies of these intrinsic discrete transitions often fail to meet the operating frequencies required for amplification, thereby restricting the performance of quantum amplifiers in terms of operating bandwidth, frequency and gain. If these difficulties can be overcome, the performance of quantum amplification technology will be significantly improved, which is of great significance for fundamental physics research—such as the detection of extremely weak electromagnetic waves and exotic particles—as well as for practical applications.

The researchers have proposed a Floquet spin quantum amplification technique, which overcomes previous limitations such as a narrow detection frequency range and achieves the amplification of extremely weak magnetic fields across multiple frequencies. This technology organically combines the ‘spin amplification technique’ and ‘Floquet modulation technique’ previously proposed by the research group, thereby extending quantum amplification technology to Floquet spin systems.

Theoretical calculations and experimental studies have demonstrated for the first time that Floquet systems can achieve simultaneous quantum amplification of multiple frequencies of the magnetic field under test by two orders of magnitude, with measurement sensitivity reaching the femto-tesla level.

The relevant technology is expected to be further extended to other quantum amplifiers, leading to the realisation of an entirely new class of quantum amplifiers—‘Floquet quantum amplifiers’. The reviewers noted that this work ‘provides an ultra-sensitive method for precision measurements and the verification of new physical laws’.