Nanoscale Infrared Light Control for Quantum Computing

Valleytronics is an emerging quantum technology that promises high-speed data processing compared to current electronics. In quantum computing based on valleytronics, valleys – local minima in the energy band structures of electrons – are used to encode, process and store information. One way to change valley states is to use infrared light. Valleytronics-based quantum computing would require low-cost infrared sources with selective control of the direction of light propagation.

Researchers from IIT Bombay have proposed a new technology platform that uses voltage to control the intensity of light emission and the direction of light propagation. It can be used to control valley states for quantum computing and also to detect chemical molecules, perform biological imaging or design a brighter light source. The researchers used a heterostructure of graphene – a two-dimensional material whose optical conductance can be controlled using voltage, and alpha molybdenum trioxide – another two-dimensional layered material whose optical properties are different in different directions – to create the platform. The study was published in the journal De Gruyter Nanophotonics. The study was funded by the Department of Science and Technology, Government of India. The current research is the first time researchers have used voltage to control light in a heterostructure of alpha molybdenum trioxide and graphene.

Two-dimensional materials are becoming increasingly important due to their unique and unusual properties, making them suitable for quantum computing and nanotechnology. They come in the form of sheets one atom thick. This sheet material has interesting properties, different from the bulk form of the same material.

The proposed heterostructure has a thin film of alpha molybdenum trioxide on a silicon substrate. Above the alpha molybdenum trioxide is a single layer of graphene attached to a terminal called the gate. The grid is used to apply voltage. The intensity of infrared emission due to the interaction of infrared light with graphene electrons can be controlled using voltage. However, more useful and exciting applications are possible if the direction and polarization of light can also be controlled. Alpha-molybdenum trioxide is an interesting material in which the permittivity of light in different directions in a plane is different. Light of a specific polarization is blocked in one direction but passes in another direction. The combined properties of the two materials give rise to a fascinating pattern of light emission in the plane of the heterostructure.

Image: The researchers’ heterostructure spontaneous emission pattern shows an interesting pattern as the gate voltage changes.

“Heterostructure offers the advantage of a large operational bandwidth and higher propagation distance that we do not get from any material individually. Along with this we can control the direction of propagation either by using the voltage, either the polarization state of the incident light, or both,” explains Dr. Saurabh Dixit, researcher of the current work.

The researchers used the Purcell effect, a quantum phenomenon that suggests that the spontaneous emission of light from a molecule can be enhanced by changing the dielectric permittivity (the ability of a material to store electromagnetic energy) of the medium that surrounds it.

“We take advantage of the Purcell effect phenomenon by using voltage to tune the dielectric permittivity of the proposed platform using graphene. Being able to control the light emission pattern of an emitter close to the proposed platform thus makes it easy to approach the valley qubit”, explains Mr. Aneesh Bapat, researcher of the current study.

The researchers used mathematical analysis and computer simulations to analyze the properties of the proposed heterostructure. They showed that the proposed platform could provide a practical way to realize valleytronics devices.

“This is an important development because the technology for applying precise voltages is already mature, even at the nanoscale. Therefore, our approach facilitates on-chip realization of valleytronics-based quantum circuits,” says Professor Kumar, who led the research.

The platform can also be used for other applications such as the detection of biomolecules and the cooling of nanoscale electronic circuits. It opens new avenues for applications in quantum interference, gate-tunable planar refraction devices, emission pattern engineering, and quantum field entanglement.

This article has been reviewed by the researchers, whose work is covered, to ensure accuracy.

Sharon D. Cole