The quantum amplification of a fragile magnetic field realized for the first time

A single measurement to sub-femtotesla level.

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Quantum amplification can accurately measure a weak electromagnetic field. However, spin quantum amplification’s limitations include readout sensitivity, coherence time, and gaseous spin initialization. These obstacles must be removed to realize quantum amplification’s full potential.

Researchers have proposed the idea of dark-state spin quantum amplification and conducted experiments in the mixed system of gaseous xenon and rubidium atoms to address this problem.

Using dark spin, a research team has achieved the first-ever quantum amplification of a fragile magnetic field, with a single magnetic field measurement accuracy of 0.1fT and a magnetic field magnification greater than 5,000.

Gaseous xenon atoms are the amplification medium in this system, while laser-polarized rubidium atoms provide the polarization and readout of the xenon nucleus spin.

Polarization, amplification, and readout are typically done simultaneously, unlike earlier studies when the mixed gaseous atoms are in the same area. By adjusting the experimental conditions, such as the xenon atom bias magnetic field and the rubidium atom polarized laser, the scientists involved in this study have discovered a novel method for separating the polarization, amplification, and readout processes.

This allows the xenon nucleus to spin in a dark state during the quantum amplification process, free from interference from the polarized rubidium atoms and with more significant potential for quantum amplification.

Scientists in this system discovered an order of magnitude longer than previously, the spin coherence period of a xenon nucleus in a dark state to be as long as 6 minutes. About 5,400 times the reported gain of the longer dark spin was applied to the weak magnetic signal. In conjunction with dark spin amplification, the atomic magnetometer allows for the realization of the sub-femtocell level of detectable magnetic field (1fT = 10-15T) in a single measurement, taking approximately 500 seconds.

This work provides insights into biomedical domains, including dark matter detection, chemical molecule quantification in fragile magnetic fields, and heart-brain magnetic diagnostics.

Journal Reference:

  1. Min Jiang et al., Observation of magnetic amplification using dark spins, Proceedings of the National Academy of Sciences (2024). DOI: 10.1073/pnas.2315696121

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