A method for reversing the Casimir force using external magnetic fields

What is known as the Casimir force or the Casimir effect is a quantum mechanical phenomenon resulting from fluctuations in the electromagnetic field between two conductive or dielectric surfaces that are separated by a short distance. Studies have shown that this force can be attractive or repulsive, depending on the dielectric and magnetic properties of the material used in the experiment.

Researchers at the University of Science and Technology of China have recently been investigating the possibility of voluntarily changing the Casimir force, in other words changing it from attractive to repulsive and vice versa, using an external magnetic field. Their research, featured in Natural Physicsshows the successful modulation of the magnetic field of the Casimir force generated by a gold sphere and a silica plate immersed in water-based ferrofluids.

“My research area is the physics of condensed matter, but I am also very interested in fundamental physics, such as fluctuations and their induced effects,” Changgan Zeng, a corresponding author of the paper, told Phys.org.

“Over the past two decades, I have closely followed developments in the field of Casimir forces, and I was very interested in the paper by Munday et al. in. Nature. Casimir forces are usually attractive, which poses challenges for applications, such as in microelectronic systems (MEMS). In their paper, the authors created an elegant experiment to achieve repulsive Casimir forces by carefully choosing the dielectric permittivity of the materials involved.”

Inspired by this earlier paper published in 2009, Zeng began to pursue further research aimed at modulating the Casimir force using magnetic fields. His hope was to develop a reliable method to correct the Casimir effect, which could open new avenues for research and technological development.

“Previously, we focused on controlling the Casimir force using an electric field, inspired by the concept of FET devices,” Zeng explained. “Although it is known that the Casimir force depends on the dielectric permittivity of the materials involved, these permits are generally not sensitive to external fields. On the other hand, according to the theory of Lifshitz, the Casimir force also depends on the magnetic permeability of the material.”

The magnetic permeability of many magnetic materials, especially ferrofluids, can be adjusted using external magnetic fields. So Zeng and his students decided to use liquid ferrofluids to facilitate the adjustment of the Casimir force between the gold sphere and the silica plate.

“I proposed this project to my graduate students, but no one was willing to implement it,” Zeng said. “Finally, I managed to convince some talented graduates to do the project, and we succeeded.”

Zeng and his students first performed a series of theoretical calculations. These calculations suggested that the Casimir force could be changed from attractive to repulsive by adjusting the external magnetic field, the distance between their two material samples and the volume of the ferrofluids they used.

The researchers then conducted an experiment designed to test their predictions. Using a cantilever that can collect measurements inside ferrofluids, they saw how the changes they implemented affected the Casimir effect.

The results of this recent study may pave the way for further efforts to effectively modify the Casimir effect using external fields. Together, these works could enable the development of new tunable micromechanical devices that enhance the Casimir force.

“We achieved modulation of the Casimir force from attractive to repulsive using a magnetic field, paving the way for the fabrication of tunable micromechanical devices based on the usable Casimir effect,” Zeng added. “In our next studies, we plan to control the Casimir force using light. For example, plasmons in metal plates can be excited by light, which should effectively change the Casimir force.”

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