doi:10.1038/nindia.2018.40 Published online 31 March 2018

Gen-next quantum devices from half-light, half-matter  

Biplab Das

A team of physicists has discovered new properties of specific particles that are composed of half-light and half-matter1. Such particles raise the possibility of making next-generation optoelectronic devices, including quantum devices that will be smarter than existing smart electronic devices.

Known as polaritons, these particles are lighter than electrons by a factor of 0.00001. “These unique particles with ultra-low masses are potentially useful for making polaritonic devices that will not dissipate heat while operating close to room temperature,” says Sajal Dhara, one of the physicists from the Indian Institute of Technology, Kharagpur, India.

Light propagates as electromagnetic waves but it also shows properties of particles with zero mass. Matter, on the other hand, is made of atoms that have mass.

It is known that mirror reflects light. When light bounces back and forth and gets trapped in the space between two mirrors, an optical cavity is formed. Exploiting this property of light, Dhara devised an experiment in which laser light was shone on a single layer of atom-thick semiconducting molybdenum diselenide trapped between two mirrors.

Collaborating with physicists from the US-based University of Rochester and India-based Tata Institute of Fundamental Research, he has shown that the mirrors form an optical microcavity inside which light gets absorbed and reemitted several times before it finally leaks out. Before leaking out, the light binds to short-lived light-emitting atom-like particles that emanate from the semiconductor. Such binding forms particles composed of light and matter that are known as polaritons.

“These particles behave like Bosons such as photons and obey a statistical law propounded by Satyendra Nath Bose and Albert Einstein,” says Dhara. Due to their ultra-low masses, these particles can reach the condensation state close to room temperature, shunning the need for creating ultra-cold temperatures close to -273oC, he adds.

This research shows remarkable coupling of light with matter, says physicist Prasanta Panigrahi from the Indian Institute of Science Education and Research in Kolkata, India. According to him, this type of system promises good applications in creating nano-scale quantum devices, particularly for information storage and retrieval.

Hailing the research, physicist G Vijaya Prakash, from the Indian Institute of Technology in Delhi, India, says that this study of strong coupling in microcavity is very interesting for understanding the basic science and identifying the scope of creating a new generation of devices based on cavity quantum electrodynamics. 

However, the most coveted application potential of the polaritons is that they could be exploited to make an ultralow-threshold laser, Prakash adds. 


1. Dhara, S. et al. Anomalous dispersion of microcavity trion-polaritons. Nat. Phys. 14, 130133 (2018)