Research

Using the concept of superconducting - normal metal - superconducting Josephson junction, we build ultrasensitive detectors which can sense photons down to single photon limit in the range of microwave energies. The noise equivalent power reported for such devices are extremely low ~ 20 zW/sqrt(Hz). While these devices are very sensitive to heat, their current state is insensitive to the energy of incoming photon. Adding the energy sensitivity feature to the detection, would bring in great potential for applications in calorimetry, such as investigating noise in different devices. Our focus in this line of research is three fold: 

1. To use material research and optimize the NEP of the device and, 

2. Establish a protocol to estimate the Cramér–Rao bound  for such detectors. 

3. Engineer the device design to make them energy sensitive in order to make an ultrasensitive spectrum analyzer.

We are also studying these devices with weak links using the Usadel equations. This approach allows us to asses if new materials can replace the existing devices in order to improve their performance. 

Not only these devices can be used to investigate the state of the qubit, they can be multiplexed and hence can contribute to the scalability issue of superconducting quantum computing. We have also used then in studying correlations of microwave photons which suggest their capability to be useful in fundamental research. They also find applications in the field of axion search. 

Our research focuses on developing high-coherence superconducting qubits through materials engineering and a detailed understanding of microscopic sources of decoherence. We investigate qubit platforms based on aluminum, niobium, tantalum, and rhenium, with particular attention to the role of two-level systems (TLSs) arising from defects at interfaces and surfaces. By studying how TLSs interact with qubit states and contribute to energy relaxation and dephasing, we aim to identify strategies to mitigate these loss mechanisms and extend qubit lifetimes. In parallel, we seek to design and optimize high-fidelity two-qubit gate operations that remain robust in the presence of material-induced noise. A complementary focus of our work is the characterization of noise generated by the qubits themselves, including fluctuations and back-action that can influence both neighboring circuits and measurement systems. Finally, we explore the use of well-characterized qubit state populations as a calibrated quantum resource for benchmarking and calibrating sensitive detectors, enabling superconducting qubits to serve as precision tools for quantum-level metrology.

In addition to materials-driven approaches, we investigate the use of high-impedance superconducting resonators as a platform for improving coherence and control in quantum circuits. High-impedance resonators provide enhanced zero-point voltage fluctuations, enabling stronger and more tunable coupling to superconducting qubits and other circuit elements. By engineering the impedance and coupling architecture of these resonators, we aim to explore new regimes of qubit–resonator interaction that can improve gate performance and enable more efficient control and readout. At the same time, high-impedance environments offer opportunities to tailor how qubits interact with their electromagnetic surroundings, potentially reducing sensitivity to environmental noise and mitigating decoherence arising from unwanted coupling to external modes. Through careful design of resonator impedance, geometry, and coupling pathways, we seek to understand how these structures can be used both as a powerful coupling resource and as a tool for engineering quieter electromagnetic environments for superconducting quantum circuits.