A pathbreaking research by IITKgp Faculty has opened up possibilities for the development of quantum devices. Prof. Sajal Dhara who joined the Department of Physics at IIT Kharagpur in 2016, has discovered negative mass particles of polaritons which are composed of half-light and half-matter.Prof. Dhara and his collaborators at the University of Rochester and ICTS, Bangalore have discovered new insights on the mass of such intriguing particles. The new understanding is expected to inspire a giant leap towards futuristic technology development.
The research has been featured in the esteemed ‘Nature Physics’ journal in their October 2017 issue. The collaborators involved in this work are Dr. C. Chakraborty, Dr. K. M. Goodfellow, Dr. L. Qiu, Dr. T. A. O’Loughlin, Prof. G. W. Wicks, and Prof. A. N. Vamivakas, all from the University of Rochester and Prof. Subhro Bhattacharjee from ICTS, TIFR.
Light is an electromagnetic wave but it also shows particle properties with zero mass.Matters on the other hand made of atoms with a certain mass. Scientists can artificially create a combined particle state that is made of half-light and half-matter, known as polaritons.
“You can imagine a caricature version of polaritons just like tiny fireflies being laws of physics which is different from our classical world,” said Prof. Dhara.
We know that light gets reflected by a mirror. Let’s imagine what will happen between two mirrors: light will bounce back and forth and gets trapped in the space between mirrors, thus forming an optical cavity. Whenever any light emitting gas of atoms, in this case, it is called excitons is placed inside the optical cavity, particles of light ( known as photons) get absorbed and re-emitted several times before it finally leaks out from the cavity. In this process, the exciton and the photon lose their individuality and forms a composite state altogether known as exciton-polaritons. Mass of such polaritons thus created is lighter than the mass of an electron by a factor of 0.00001.
This unique ultra-low mass properties of these particles are what would lead to the possible devices of future dissipation-less polaritonic devices close to room temperature or as a householder would put as ‘ushering an era which will witness a giant leap from smart electronic to smarter polaritonic devices, realizing the dream – the future is here.’ This research will also lead to the development of a new generation of optoelectronic devices.
Exciton-polaritons are Bosons which obey the well-known Bose-Einstein statistics discovered by S. N. Bose and A. Einstein who also predicts an interesting condensation state of such particles known as Bose-Einstein condensation (BEC).
“So far BEC has been achieved at ultra-cold temperatures close to -273 degree Celsius (absolute zero). One of the main interests in this field is due to the possibility of realization of Bose-Einstein Condensation of gas made of exciton-polaritons closer to room temperature. This will open up possibilities for the development of quantum devices. We can now imagine dissipation less polaritonic devices in future that can work at room temperature” said Prof. Dhara who is the leading author of the paper.
The new findings that the work presented by Prof. Dhara and coworkers shows that the particles not only have ultra-low mass but it can also become negative if the particles become charged up with additional electrons.
Prof. Dhara has received substantial funding from MHRD, ISIRD and the SERB Ramanujan Fellowship research grant for developing his lab facilities at IIT Kharagpur. One of the long-term goals of the ‘Nanoscale Optoelectronics’ lab would be to investigate the light-matter interaction for the development of futuristic technologies and basic science.