Research
A brief on some of the projects from our group.
Few qubit devices for quantum computing:
Among the different implementations of quantum computing such as solid-state systems, magnetic-resonances, and ion-traps, superconducting qubits have emerged as the front-runner for the realization of a scalable quantum computer. Superconducting qubits have shown their potential in realization of proof-of-concept experiments to the demonstration of quantum-supremacy.
We are currently developing planar superconducting qubit devices with a focus on the design and fabrication protocols to improve their coherence times, and to design coupled qubit devices with focus on improving the performance of two-qubit gates.
An X-mon style qubit coupled to readout resonator (left). A picture of low temperature setup for the measurement of superconducting devices.
Hybrid electro-mechanical systems:
We are looking into Transmon-type superconducting qubit coupled a variety of the mechanical systems such as nanowire resonator (essentially guitar strings at nanoscale), drumhead shaped resonators, and piezoelectric resonators. The NEMS resonators can be designed to achieve very high-quality factor. Riding on the progress made in controlling superconducting qubits, we are trying to push the limits on the control of macroscopic mechanical resonators in the quantum limit. In the quantum regime, the NEMS resonators show exquisite sensitivity to various forces. Moreover, being macroscopic in size, the quantum states of the NEMS devices allow to probe the quantum mechanics at increasingly large mass and length scales.
Scanning electron microscope image showing a thin nanowire (length ~ 50 micron) embedded into a transmon qubit (not shown here). The vibrations in the nanowire can last up to ~100ms.
Electromechanics using 3D microwave cavities:
Light carries momentum and hence when shined upon something imparts a very small force to it. With appropriate intensity of light, this imparted force can be made "strong" enough to manipulate the state of mechanical resonator down to the quantum regime.
We are exploring the coupling between an electromagnetic mode of a 3-dimensional superconducting microwave cavity and a drumhead-shaped mechanical oscillator, suspended with the help of clamps. The resonator is implemented using a mechanically compliant parallel plate capacitor. To simply put, this whole system becomes equivalent to a LC oscillator and this supports a microwave mode. The mechanical vibration changes the capacitance of the LC oscillator, and thus frequency modulates the cavity resonant frequency.
The coupling between electromagnetic mode and mechanical vibrations can pushed into strong-coupling regime, where "light-like" and "vibration-like" modes loose their individual character, leading to the onset of hybridized states. Such coupling strengths are necessary to enable a larger control of the motion in quantum regime.
A drum-head shaped mechanical oscillator of diameter ~ 20 micron and fabricated with Aluminum. The plot below shows the hybridization between mechanical motion and microwave photons
Cavity-optomechanics with novel materials:
Cavity-optomechanics based approach has been very successful in increasing the displacement sensitivity of various nano-electro-mechanical systems. These techniques manifest themselves in experiments dealing with the detect of gravitational waves to the detection of displacement beyond the standard quantum limit. Such systems can also be implemented in the microwave-domain, and thus offer a unique platform to perform sensitive detection of forces in mesoscopic devices.
In this project, we are investigating the change in elastic response of a high-Tc superconductor when placed in small magnetic field. Unlike a type-I superconductors, HTS allows partial penetration of magnetic field lines above Hc1. While it may seem that penetration of the magnetic flux should not affect the elastic response, it turns out that it does change the electromechanical response in the mixed state. We are exploring if cavity-optomechanical techniques can be used detect the subtle change caused by electric-charges associated with vortex-cores.
This project has been led by Sudhir Kumar Sahu.
False color scanning electron microscope image showing a BSCCO flake (HTS material shown in green) transferred to a microwave cavity (red-color, complete image is not shown here).