Research

At the heart of our research is a unique and powerful tool: the Nitrogen-Vacancy (NV) center. Think of it as a single, atomic-scale flaw within a diamond's crystal structure that acts as a precise quantum sensor. What makes the NV center revolutionary is that, unlike many quantum systems, it works perfectly in ambient, room-temperature conditions.

By using laser light and microwaves, we can control and "read" the state of this single atom. This allows us to detect tiny changes in its local environment, making it an ideal probe for sensing at the nanoscale.

Our Approach: From Nanoparticles to Thin Films

Our group engineers these diamond sensors in two primary forms to tackle different challenges:

• Nanodiamonds: We use tiny, free-floating diamond particles (less than 100 nm wide) that each contain one or more NV sensors. These are biocompatible and can be used as mobile probes inside living cells or dispersed in chemical solutions.

• Thin Diamond Films: We engineer custom diamond chips with a dense layer of NV centers just beneath the surface. This creates a "quantum camera" that can map physical quantities—like temperature or magnetic fields—over a wide area with incredible detail.

Applications: From Biology to Electronics

We apply these quantum platforms to solve cutting-edge problems across multiple disciplines:

• Quantum Biosensing: We use our biocompatible nanodiamonds to explore the inner workings of living cells. This allows us to measure temperature changes during biological processes or track specific molecules and free radicals, all at the sub-cellular level without using toxic labels.

• Nanoscale Thermometry: The NV center is an exceptional thermometer. We use it to map "hotspots" on active microchips with nanoscale resolution and to study how heat flows in novel materials.

• Magnetic & Electric Field Sensing: The NV spin is highly sensitive to local fields. We harness this to map the faint magnetic signals from new materials or even to detect the activity of neurons.

• Chemical Relaxometry: By measuring how the NV center's quantum state "relaxes," we can detect and identify fluctuating magnetic signals. This technique provides a unique way to "listen in" on chemical reactions or identify specific ions in a solution.

Single-Photon Sources for Quantum Technology

Beyond sensing, the NV center is also a world-class source for emitting single "particles" of light (photons). These single-photon emitters are the fundamental building blocks for future quantum computers and unhackable quantum communication networks.

A key challenge is efficiently collecting every photon that the NV center emits. Our group designs and fabricates nanoscale "photonic" structures—like tiny light-guides and resonant cavities—directly into the diamond. This technology acts as a funnel, channeling the light and creating the bright, reliable sources needed for next-generation quantum information systems.

In past two decades or so, the technology related to photonics have seen tremendous growth in terms of miniaturization which is comparable to transformation happened with the electronic systems: Reducing it from bulky devices to atomic scale transistors on a single chip. The current technology is in a position to integrate optical circuits/components on a microchip. In fact, a small survey can easily reveal that the well-known Moore’s law can readily be applicable in photonic integrated circuits (PICs). Driven by the advancement in microfabrication, the commercialization of this architecture is now a reality and some of the world’s leading companies are into it. However, the main challenge with the classical PICs is scaling up on integrated platform and engaging laboratory-based innovations to real-life problems.

An emerging subset of integrated photonics circuits since 2008 is integrated quantum photonics which employs same classical PICs for quantum applications. At present different approaches have been adopted to make the quantum circuits on monolithic or hybrid platforms. Photonic Integrated Circuit Group at CQuERE deals with the applied aspects of photonics on an integrated platform. Our group is involved in studying novel properties of light on a chip-scale to develop technology for translational research. We seek to encompass both technological domains viz., classical and quantum. In context to quantum research, PICs has potential applications in quantum sensing, quantum communication, quantum information research, and quantum metrology. The research on integrated circuits for quantum photonics can be categorized into three main areas viz. quantum light sources, photonic integrated circuit platform, and single photon detectors. Currently, some of the research that we plan to pursue are: (i) Chem/bio sensing using PICs, (ii) single photon emitters in telecommunication wavelengths, and (iii) quantum (/classical) computing. Eventually we intend to extend our research on quantum networks as well.

Chem/bio sensing:

The area of bio-sensing is developing fast and has a lot of scopes to do new things. The truly interdisciplinary nature fits well into TCG CREST’s research motto and can be directly applied to human life. The idea is to develop is chip-based interferometric measurement platform that can work as a sensor for biological proteins, or a trace element present in the water solution. This approach can be fast with high degree of accuracy. The whole sensing scheme can be improved by using non-classical states of light. We are also exploring the possibility of using non-Hermitian systems for quantum enhanced sensing applications.

Single photon emitters:

Recently, single-photon emitters (SPE) have become prime candidate for research in integrated quantum optics and implementation of quantum technologies. Different materials are currently being investigated viz. epitaxial quantum dots, Colloidal quantum dots (CQDs), point defects in various semiconductors like diamond, silicon carbide, hexagonal boron nitride. Although epitaxial QDs suffers from integration-related problem with other quantum technology platforms, CQDs shows great potential due to its tunability over emission wavelength including telecom range by varying the sizes and composition. In addition, CQDs offer great flexibility to be integrated with existing quantum technology platforms for its solution-based synthesis processing routes. At present, our group is actively working on CQDs and point defect based SPEs.