Physicists Have Created Particles That Exhibit Negative Mass

If you push something, it will move in the direction of force applied. But if you push an object with negative mass, it will move against the direction of applied force. Creating a particle with negative mass seems practically impossible and most has only been demonstrated in theoretical analyses. Now, physicists at University of Rochester say they have developed a device that can create particles with negative mass.

This alone is “interesting and exciting from a physics perspective,” explained Nick Vamivakas, an associate professor of quantum optics and quantum physics at Rochester’s Institute of Optics. “But it also turns out the device we’ve created presents a way to generate laser light with an incrementally small amount of power.”

For the study, the team used a device that consisted of two mirrors facing each other. Apparently, this arrangement allowed researchers to create an optical microcavity, which confines light at different colors of the spectrum depending on how much space is maintained between mirrors. In the device’s optical microcavity, the team embedded atomically-thin molybdenum diselenide semiconductor and it was placed in such a way it could interact with the confined light.

They found that interaction between the semiconductor and the confined light resulted in small particles from the semiconductor—called excitons, which later combined with photons from the confined laser light to form polaritons, which have negative mass.

“By causing an exciton to give up some of its identity to a photon to create a polariton, we end up with an object that has a negative mass associated with it,” Vamivakas explained. “That’s kind of a mind-bending thing to think about, because if you try to push or pull it, it will go in the opposite direction from what your intuition would tell you.”

Although practical applications for the device are still down the road, Vamivakas said his team would continue to explore how the device might help create lasers that doesn’t require much energy, and the physical implications of creating negative mass in the device.

“With the polaritons we’ve created with this device, the prescription for getting a laser to operate is completely different,” said Vamivakas. “The system starts lasing at a much lower energy input than traditional lasers now in use.”

“We’re dreaming up ways to apply pushes and pulls—maybe by applying an electrical field across the device—and then studying how these polaritons move around in the device under application of external force.”

The study, entitled “Anomalous dispersion of microcavity trion-polaritons” has been published in the journal Nature Optics.

Source: University of Rochester