This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Gravity, the attraction between objects with mass, is the weakest of the four fundamental forces governing physical processes. Detecting the tiny gravitational pull of objects that are just a few millimeters in size and have a very small mass is extremely challenging.
Reliably measuring the gravitational fields of microscopic objects could open new possibilities for research and the development of new technologies. For instance, it could allow physicists to explore how gravity relates to quantum physics and develop new instruments to study tiny objects. Researchers at Shanghai Jiao Tong University and other institutions recently developed a new sensor that can detect the gravitational pull of millimeter-sized objects.
This sensor, introduced in a paper published in Nature Nanotechnology, is based on a suspended structure called a torsion pendulum and an optical microcavity, a structure that confines light. "Our group has been working for several years on slow and stopped light in optical micro cavities," said Yicheng Zhu, co-author of the paper. "In our previous work, we found that near the stopped-light condition, the optical phase becomes extremely sensitive to very small perturbations.
This made us wonder whether such strong dispersion could be used not just to control light, but as a practical resource for precision sensing. Gravity was a particularly attractive test because the gravitational force generated by a millimeter-scale object is extraordinarily weak." The new sensor developed by the researchers uses a suspended structure that turns by twisting its support, known as a torsion pendulum. The gravitational pull of a nearby object causes a small movement in this structure, which the team's sensor then measures using an optical microcavity.
"The basic idea is similar to the classic Cavendish experiment, but we use an optical microcavity as the readout," said Zhu. "A small source mass produces a tiny gravitational force on a torsion pendulum. This slightly moves a silica microsphere relative to a tapered optical fiber.
Because the gap between them is only around 100 nanometers, even a very small displacement can noticeably change their optical coupling." Light inside the microcavity is linked with vibrations. The coordinated response between packets of light and of vibrational energy strongly alters how light travels through the cavity. "We then operate the microcavity near the stopped-light point, where the optical phase changes extremely rapidly with frequency," explained Zhu.
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