Scientists at Caltech have conceived a new type of “quasiparticle”, known as topolariton, which could pave the way for more efficient photonic devices, such as photovoltaic cells, displays, optical amplifiers as well as barcode scanners, that can easily detect, produce and manipulate light. Developed by Gil Refael, a theoretical physics and condensed matter theory professor, the research outlines the potential of an entirely new kind of half-matter, half-light particle in ushering significant scientific and technological advancements.
The team first came upon the idea, for the theory, back in 2010 during a National Science Foundation (NSF)-funded workshop at the Institute for Quantum Information and Matter. Recently published in the Physical Review X journal, the research is closely related to Refael’s work on quantum matter, particularly regarding quantum entanglement, computing and the development of new quantum states. It addresses one of the primary drawbacks of semiconductors used in modern electronics: loss of energy via heat due to resistance.
Although such problems do not exist in case of light transmission, there are other causes that contribute to signal loss, including irregular reflection and scattering of light particles, i.e. photons. According to the researchers, the new quasiparticle could not only reduce the occurrence of signal degradation, but could also improve stability of the photons traveling along the sides of a semiconductor. Existing only in solid materials, quasiparticles are dynamic emergent entities that share some of the properties of fundamental particles, like electrons and quarks present inside an atom.
One example of quasiparticle is polariton, which is formed as result of the interaction between photons and excitons (basically, the state when an electron and an electron hole are bound together by means of an electrostatic Coulomb force). Topolaritons are a type of polariton, capable of flowing in a single direction along the sides of semiconductor quantum wells placed in optical cavities. The setup ensures that the electrons and the photons move in the same plan. Speaking about the research, the scientists explained:
We suggested that you could take a simple semiconductor and a regular quantum well, and give rise to a special excitation, which is a hybrid of a photon and an electron-hole pair. Shining light at the frequency can kick an electron out of the balance and initiate a polariton that travels exclusively on the edge of the system. The light–matter interaction, in this case, produces so-called topological quantum states that are not there in each of the components.
Comprised partially of light and matter, the topolaritons can be steered with the help of reflectors or photonic band gaps, which are specific areas in an optical medium that are impervious to photons. What is more, the photons can be made to travel in the opposite direction, by applying a magnetic field of a particular magnitude. Once developed, the technology could be used to built more efficient semiconductor devices. The team added:
This would be like a one-way filter for light, providing a directional communication with minimum losses of energy.
When it comes to efficiency and accuracy, photonic devices are more advanced than currently-available varieties of semiconductors. Furthermore, they can function over longer distances, save larger amounts of energy and are also, less susceptible to external influences, like electromagnetic fields. While it could indeed usher a new age of incredibly-efficient electronics, the technology currently exists only as theory. Getting it ready for real-life applications is still quite a long way off. Refael said:
We’ll need to create some new interfaces between the photonic world and the electronic world. One challenge is making one-way photon wave-guides for visible light. The topolaritons provide a route to such devices using standard semi-conductor technology, and can also act as an intermediary between photonic and electron-based devices—a necessary step for any optoelectronic device.