Hybrid qubits
We aim to use quantum materials as the accelerator to push the limit of quantum circuits such as amplifiers and qubits. We seek to develop devices with new functionalities that would allow operation in unexplored regimes, including temperatures above a few Kelvin and frequencies above 100 GHz.
We build hybrid qubits through a delicate combination of materials research, microwave engineering, and a dash of condensed matter physics.
Understanding the ‘why’ of materials is essential to using them as components in coherent quantum circuits. Addressing questions in condensed matter physics, such as the breakdown of superconductivity through various tuning parameters, helps us carefully understand a material’s electronic properties that we can then utilize to develop quantum circuit elements.
For example, superconducting qubits are built from linear and nonlinear circuit elements. Often the choice of nonlinear components is the Josephson tunnel junction. This element is comprised of two superconducting electrodes separated by an insulating tunnel barrier. Some materials offer both of these phases, which we can exploit by understanding the mechanism that leads to a clean breakdown of superconductivity into an insulating phase without intervening dissipative quantum phases. Using intrinsic electronic phases of a material allows us to build monolithic circuits from high gap materials for higher temperature and frequency operations.
Other ways to build nonlinear circuit elements rely on the intrinsic nonlinearity associated with the superconducting condensate. This is described by the kinetic inductance of the material, which can be natural very large in some materials such as low-dimensional superconductors, including 2D materials and proximity-coupled hybrid structures such as superconducting-semiconducting nanowires. Such material systems further offer electrostatic tunability over their superconducting properties which allow us to build fully configurable and controllable quantum devices.