Research
Hybrid Material of Artificial Spin Ice and Type-II Superconductor
Geometric frustration emerges when local interaction energies in an ordered lattice structure cannot be simultaneously minimized, resulting in a large number of degenerate states. However, it is difficult to achieve very high degeneracy, especially in a two-dimensional system. By coupling type-II superconductors with an artificial spin ice structure, we realized in situ controllable geometric frustration with high degeneracy in a two-dimensional flux-quantum system. The tunable magnetic charges in the artificial spin ice strongly interact with the flux quanta in the superconductor, enabling switching between frustrated and crystallized flux quanta states.
Confined Vortex Matter
When Abrikosov vortices are placed in a large container, they are arranged in a triangular lattice, just similar to the bulk case. However, when the container is small, typically of the size comparable with penetration depth, the configuration they form is strongly influenced by the container symmetry. Besides configuration, other properties of vortex matter can also be quite different when confined in a mesoscopic container. Here, I use computer simulations to study mesoscopic confined vortex matter. The methods include Molecular Dynamics, Gradient Descent, Eigenvector Following, Complex Network Science, etc. In particular, I developed efficient methods to find local minima and first-order saddle points in a high-dimensional function, which is then applied to potential energy function in terms of vortex positions. These critical points are then connected to form a complex network representation of the potential energy landscape. With transition barrier on each edge, this is a concise representation encoding the system dynamics. I'm using this method to study the "magic number" problem, i.e. extraordinary stable states at some specific numbers of vortices.
Single Vortex Manipulation
Manipulation of individual vortices in type-II superconductors can now be achieved via a variety of methods, including local magnetic fields, magnetic force microscopes (MFMs), mechanical forces, scanning tunneling probes, and optically induced local heating. It is possible for the vortices to be moved over certain distances, entangled, and arranged in special positions. The forces induced on the tip by the vortices can also serve as a probe of the pinning properties, the dynamics of individual vortex coupled to pinning, or the creation of vortices. As advances in nanoscale fabrication continue, it will likely become possible to develop even more precise control of the vortex motion as well as to manipulate multiple vortices at the same time. One promising application of vortex manipulation is to perform the braiding of Majorana fermions for quantum computing in materials for which Majorana fermions are localized in the vortex core.
Quantum Computation
- Quantum dynamics of tunneling junctions
- Effect of non-ideal material conditions in quantum devices
- Quantum simulation with IBM NISQ machines