Polaritons are special, half-light, half-matter quasi-particles that can be created when light interacts intensely with matter. The realisation of polaritons in optical cavities and its potential for the creation of high-performance lasers and other technologies have been studied by physicists recently.
A very effective device that can produce and amplify microwaves was recently invented by University of Manitoba researchers. The gadget is based on cavity magnon polaritons. This device, described in Physical Review Letters, was found to perform substantially better at room temperature for coherent microwave emission and amplification than earlier proposed solid-state devices.
“In 1992, Claude Weisbush, a French semiconductor physicist working in Japan, discovered cavity exciton polariton by confining light in a quantum microcavity to interact with semiconductors,” Can-Ming Hu, the researcher who directed the study, told Phys.org.
“This led to the invention of polariton lasers with superior performance that have transformed solid-state laser technology. Two decades later, the magnetism community re-discovered cavity magnon polariton by confining microwaves in a cavity to interact with magnetic materials, such a half photon and half magnon quasi-particle was first discovered by Joe Artman and Peter Tannenwald in 1955 at MIT, which went largely unnoticed until recently.”
Coherent on-chip microwave sources are necessary for technologies such as wireless communication and quantum information. Hu and his coworkers were inspired by this necessity to investigate the potential application of cavity magnon polaritons for high-quality microwave emission and amplification.
“Intrigued by the resemblance between cavity magnon polariton and cavity exciton polariton, I became curious whether the cavity magnon polariton might help us to make better solid-state microwave sources,” Hu said. “So, in 2015, my group launched a study to explore microwave emission of cavity magnon polaritons.”
The goal of the initial research was to build a coherent microwave emission system based on cavity magnon polaritons. In the end, they sought to outperform those described in earlier works while maintaining the stability and controllability of their hybrid light-matter coupled technology.
“First, we follow the principle proposed in 1920 by Dutch physicist van der Pol: using nonlinear damping to balance gain in an amplified oscillatory system, one can design and optimize a stable gain-driven cavity,” Bimu Yao, an associate professor from the Chinese Academy of Sciences who carried out this study at the University of Manitoba, told Phys.org. “Then, we set a magnetic material into such a gain-driven microwave cavity, letting the amplified microwaves to strongly interact with magnons.”
A new kind of polariton known as a “gain-driven” polariton is created in the researchers’ system by the robust interaction between amplified microwaves and magnons. This gain-driven polariton has a stable phase as opposed to the ordinary polaritons realised in earlier investigations, which allows for the coherent emission of microwave photons.
“For decades, the magnetism community has been working on spin-toque oscillator (STO), which is a solid-state device that utilizes magnons to produce coherent microwaves,” Yongsheng Gui, a research associate at the University of Manitoba who carried out the study, told Phys.org. “The major hurdle is that the emission power of the STO is typically limited to less than 1 nW. Our device’s output is a million times more powerful, and the emission quality factor is a thousand times better.”
This study team’s proof-of-principle gadget performed admirably in preliminary tests, exceeding both STOs and solid-state masers constructed in the past. Masers are machines that create or enhance microwave radiation by stimulating atoms to emit radiation.
“Outside of the magnetism community, there have been divers efforts for developing masers,” Gui said. “Compared with the best solid-state maser, our device’s output is a billion times more powerful, with a comparable emission quality factor.”
Hu and his team may have discovered a novel gain-driven polariton that could create intriguing new opportunities for the creation of extremely effective solid-state microwave sources that can be integrated on-chip. These polariton microwave sources are not only small but also frequency programmable thanks to the amazing controllability of light-matter interaction. In the future, they might be incorporated into a variety of technologies and gadgets, including as quantum computers and wireless communication networks.
“As the physics of gain-driven light-matter interaction is new, our study may also lead to new discoveries beyond microwave applications,” Hu added. “We have now submitted a patent application, and my students are working on developing prototype devices together with industry partners.”
