We perform theoretical studies on various topics in condensed matter physics, quantum computing, and complex systems. We have successfully predicted and/or explained numerous experimental results in solid-state physics, particularly on superconducting systems, and have proposed new applications and solutions for several experimental problems. Most of our current research is related to either quantum computing or vortex dynamics, which is described in more detail below.

Quantum Computing - Superconducting Qubits

Quantum information science is a very active area of research. A qubit is a quantum two-level system that can be operated as a computational unit. It is the fundamental building block for proposed quantum computers. Very promising candidates are qubit designs using superconducting electrical circuits. Advantages of these include: potential scalability, controllable interactions, integration with classical electrical circuits, etc. There are also difficulties such as decoherence and cross-talk among qubits. We are currently working on understanding, improving and suggesting new solutions to overcome problems in qubit designs.

Talks and presentations

Nanjing June 18th 2006 - Superconducting Qubits [PDF]

Dresden July 2006 - Superconducting Qubits [PDF]

Our published work is available in the "Publications" link of these web pages, and also online via the ISI (web of science) database. A small selection of our current work on qubits is presented in the talks listed above, and a pedagogical summary of one of our past projects is available below.

Coupling and Scalability

Mechanical Qubits (Japanese version here).

For a complete list of publications in quantum computing, please click here.

Vortex Dynamics

Superconductors generally expell magnetic fields, but when the magnetic field is strong enough (H>Hc1) it penetrates the superconductor in the form of quantized flux lines, called vortices. We are studying novel ways to improve properties of superconductors, such as the critical current, by using so-called pinning centers that can trap vortices, minimizing energy dissipation. The dynamics of such vortices can be controlled, and it can be used for various kinds of applications. We have proposed several devices using vortex dynamics, such as pumps, magnetic lenses, and vortex diodes/rectifiers. We are also studying the generation, detection, and filtering, of terahertz radiation using Josephson vortices.

A selection of our vortex related work is presented in the following pages:


Posters on THz radiation, superconducting vortices, magnetic vortices on nano-disks, and particle motion control:

Magnetic and mechanical buckling: modified Landau theory approach to study phase transitions in micro-magnetic disks and compressed rods [PDF]

Controlling the motion of tiny particles and magnetic flux quanta [PDF]

Surface Josephson plasma waves in layered superconductors and THz detectors [PDF]

Using Josephson Vortex Lattices to Control THz Radiation: How to generate, filter, and detect radiation using layered superconductors [PDF]

Surface Josephson plasma waves in layered superconductors and THz detectors [PDF]

Reversible Rectifier that Controls the Motion of Magnetic Flux Quanta in Superconductors

An introduction to results published in Science 2003 (html, pdf).

A This week in science article and a corresponding Enhanced perspective feature.

Crossing vortex lattices in very anisotropic superconductors

Nature Materials 2002 (html, pdf) with a News and Views feature (html, pdf).

Nature Materials 2006 (html, pdf) with a News and Views feature (html, pdf).

A news feature from the University of Michigan (local).

Vortex Dynamics Animations:

AC lensing of vortices

DC lensing of vortices:

- Continuous playing

- Stages (click on arrow to play)

See also News and Views Nature Physics 2006 (html, pdf).

For a complete list of publications in vortex dynamics, please click here.